Combined nut for double-end bolt and double-end bolt assembly

Abstract

The invention provides a combined nut for a double-end bolt and a double-end bolt assembly, and belongs to the technical field of bolt connection. The combined nut comprises a protection nut embedded in the structure body and a breakage nut connected with the end, stretching out of the structure body, of the stud, the crest width of an internal thread of the protection nut is Cnb, the root width of the internal thread of the protection nut is Cnb2, the height of the internal thread of the breakage nut is hnb, the crest width of an internal thread of the breakage nut is Cnd, the root width of the internal thread of the breakage nut is Cnd2, the height of the internal thread of the breakage nut is hnd, and Cnb is larger than 0 and smaller than Cnd. The rigidity of the internal thread teeth of the protection nut is smaller than that of the internal thread teeth of the broken nut, the bending deflection of the internal thread teeth of the protection nut is larger, and when the stud assembly bears an alternating load, the internal thread teeth of the protection nut can generate larger bending deformation to absorb inertia force generated by the alternating load, so that the stability of the stud assembly is improved. And the fatigue performance of the external thread of the stud at the protective nut is improved, so that the probability that the fracture position occurs at the fracture nut is higher.

Description

Technical Field

[0001] The invention relates to a combined nut for a stud bolt and a stud bolt assembly, belonging to the technical field of bolt connection. Background Art

[0002] The stud bolt assembly is a common bolt fastener with a simple structure, easy to use, and a wide range of application scenarios. For example, the anchor bolts and blade bolt assemblies in the wind power industry are stud bolt connection structures. The blade bolts can refer to the wind turbine blade root structure and blade disclosed in the Chinese utility model patent with authorization announcement number CN202431457U, in which the blade root is pre-embedded with an embedded nut, one end of the stud bolt extends into the blade root and connects with the embedded nut, and the other end extends out of the blade root. It is fixed to the pitch flange by the fastening nut during installation. The embedded nut, fastening nut and stud bolt constitute a stud bolt assembly, and the internal thread pitch of the embedded nut and the fastening nut is equal to the external thread pitch at both ends of the stud bolt.

[0003] During the operation of a wind turbine, as the blades are stressed, the stud bolts at the root of the blades will be subjected to alternating loads such as impact and vibration. Under the action of alternating loads, the stud bolts may break in extreme cases. The fracture position of the stud bolts is random. It may break at the first thread that matches the embedded nut, or it may break at the first thread that matches the fastening nut. At present, it is impossible to accurately predict the fracture position of the stud bolts. If the fracture position of the stud bolt is located at the matching position with the fastening nut, the stud bolt still has a part that overhangs outside the blade. Using this part as the force application position, it is relatively easy to remove the remaining stud bolts from the root of the blade and then replace them with new stud bolts. However, if the fracture position of the stud bolt is located at the matching position with the embedded nut, the broken bolt head is attached to the embedded nut and located inside the blade, making it very difficult to remove, which brings great trouble to the on-site replacement operation. Of course, if the embedded nut is embedded in other structures, such as the concrete foundation under the wind turbine tower, if the embedded part of the stud bolt (also called wind turbine anchor bolt) breaks, the same technical problem exists. Summary of the invention

[0004] The object of the present invention is to provide a combination nut for stud bolts to solve the problem that the fracture position of the existing stud bolts cannot be predicted, resulting in the broken bolt head being located inside the structure when the fracture position of the stud bolt is located at the matching position with the embedded nut, which is very difficult to remove and causes great trouble to on-site replacement operations; the object of the present invention is also to provide a stud bolt assembly to solve the above-mentioned problem.

[0005] To achieve the above purpose, the combined nut for stud bolts in the present invention adopts the following technical solution:

[0006] A combination nut for stud bolts, comprising a protection nut for pre-embedded in a structure and a breaking nut for connecting with one end of the stud bolt extending outside the structure, the internal threads of the protection nut and the breaking nut are both metric threads or MJ threads, and the tooth profiles of the internal threads both include a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the internal thread minor diameters of the protection nut and the breaking nut are both equal, the tooth angles are both 60°, the pitches are both P, and the internal thread top width of the protection nut is defined as C nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd , then 0<C nb <C nd ,

[0007] The beneficial effect of the above technical solution is that: the present invention is a pioneering invention, and the combined nut for stud bolts proposed in the present invention includes a protective nut and a breaking nut, the protective nut is pre-buried in the structure, and the breaking nut is connected to the end of the stud bolt extending outside the structure, and measures are set to ensure that the end of the stud bolt assembly that cooperates with the protective nut will not break when subjected to alternating loads, while the end that cooperates with the breaking nut will break. Specifically, the inner thread minor diameter, tooth profile angle and pitch of the protective nut and the breaking nut are equal, and the inner thread crest width C of the breaking nut is equal to the inner thread crest width C of the breaking nut. nd The internal thread crest width of the protective nut is C nb Satisfy 0<C nb <C nd , while the internal thread crest width C of the broken nut nd The width of the tooth bottom is C nd2 Maintaining a certain geometric relationship, the internal thread crest width of the protective nut is C nb The width of the tooth bottom is C nb2 Maintaining a certain geometric relationship, the tooth thickness of the internal thread teeth of the protective nut is thinned, and the tooth thickness of the internal thread teeth of the protective nut is smaller than the tooth thickness of the internal thread teeth of the broken nut. In this way, the stiffness of the internal thread teeth of the protective nut is smaller than the stiffness of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is greater. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external thread teeth of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture occurring at the broken nut is greater, and the stud bolt can be easily removed from the structure, facilitating on-site replacement operations.

[0008] Furthermore, C nd <C0, C0 is the crest width of standard metric internal thread or MJ internal thread.

[0009] Furthermore, the internal threads of the protection nut and the breaking nut are both metric internal threads for use with standard metric external threads. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C nb <C nd ≤0.125P.

[0010] Furthermore, the internal threads of the protection nut and the breaking nut are both MJ internal threads for use with standard MJ external threads. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C nb <C nd ≤0.125P.

[0011] Further, h nb >h nd , h0 is the tooth height of standard metric internal thread or MJ internal thread.

[0012] Furthermore, the internal threads of the protection nut and the breaking nut are both metric internal threads for use with standard metric external threads. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, and 0.464P+0.619C is obtained. nb ≤h nb , 0.464P+0.619C nd ≤h nd .

[0013] Furthermore, the internal threads of the protection nut and the breaking nut are both MJ internal threads for use with standard MJ external threads. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, and 0.412P+0.6C is obtained. nb ≤h nb , 0.412P+0.6C nd ≤h nd .

[0014] Furthermore, the internal thread of the broken nut is a standard metric internal thread, and the internal thread of the protective nut is an improved metric internal thread for use with a standard metric external thread. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C nb ≤0.125P.

[0015] Further, 0.464P+0.619C nb ≤h nb .

[0016] Furthermore, the internal thread of the broken nut is a standard MJ internal thread, and the internal thread of the protective nut is an improved MJ internal thread for use with the standard MJ external thread. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C nb ≤0.125P.

[0017] Further, 0.412P+0.6C nb ≤h nb .

[0018] To achieve the above purpose, the stud bolt assembly in the present invention adopts the following technical solution:

[0019] A stud bolt assembly comprises a stud bolt and a combination nut used in conjunction with the stud bolt, wherein the external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same, the combination nut comprises a protection nut used for pre-embedded in a structure and a breaking nut used for connecting with one end of the stud bolt extending outside the structure, the internal threads of the protection nut and the breaking nut are metric threads or MJ threads and the tooth profiles of the internal threads include a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the internal thread minor diameters of the protection nut and the breaking nut are equal, the tooth angles are both 60°, the pitches are both P, and the internal thread top width of the protection nut is defined as C nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd , then 0<C nb <C nd ,

[0020]

[0021] The beneficial effect of the above technical solution is that: the present invention belongs to an improved invention, further defining the combination nut including a protective nut and a breaking nut, the protective nut is pre-buried in the structure, the breaking nut is connected to the end of the stud bolt extending outside the structure, and measures are set to ensure that the end of the stud bolt assembly that cooperates with the protective nut will not break when subjected to alternating loads, while the end that cooperates with the breaking nut will break. Specifically, the inner thread minor diameter, tooth profile angle and pitch of the protective nut and the breaking nut are equal, and the inner thread crest width C of the breaking nut is equal to the inner thread crest width C of the breaking nut. nd The internal thread crest width of the protective nut is C nb Satisfy 0<C nb <C nd , while the internal thread crest width C of the broken nut nd The width of the tooth bottom is C nd2 Maintaining a certain geometric relationship, the internal thread crest width of the protective nut is C nb The width of the tooth bottom is C nb2 Maintaining a certain geometric relationship, the tooth thickness of the internal thread teeth of the protective nut is thinned, and the tooth thickness of the internal thread teeth of the protective nut is smaller than the tooth thickness of the internal thread teeth of the broken nut. In this way, the stiffness of the internal thread teeth of the protective nut is smaller than the stiffness of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is greater. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external thread teeth of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture occurring at the broken nut is greater, and the stud bolt can be easily removed from the structure, facilitating on-site replacement operations.

[0022] Furthermore, C nd <C0, C0 is the crest width of standard metric internal thread or MJ internal thread.

[0023] Furthermore, the internal threads of the protection nut and the breaking nut are both metric internal threads for use with standard metric external threads. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C nb <C nd ≤0.125P.

[0024] Furthermore, the internal threads of the protection nut and the breaking nut are both MJ internal threads for use with standard MJ external threads. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C nb <C nd ≤0.125P.

[0025] Further, h nb >h nd , h0 is the tooth height of standard metric internal thread or MJ internal thread.

[0026] Furthermore, the internal threads of the protection nut and the breaking nut are both metric internal threads for use with standard metric external threads. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, and 0.464P+0.619C is obtained. nb ≤h nb , 0.464P+0.619C nd ≤h nd .

[0027] Furthermore, the internal threads of the protection nut and the breaking nut are both MJ internal threads for use with standard MJ external threads. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, and 0.412P+0.6C is obtained. nb ≤h nb , 0.412P+0.6C nd ≤h nd .

[0028] Furthermore, the internal thread of the broken nut is a standard metric internal thread, and the internal thread of the protective nut is an improved metric internal thread for use with a standard metric external thread. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C nb ≤0.125P.

[0029] Further, 0.464P+0.619C nb ≤h nb .

[0030] Furthermore, the internal thread of the broken nut is a standard MJ internal thread, and the internal thread of the protective nut is an improved MJ internal thread for use with the standard MJ external thread. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C nb ≤0.125P.

[0031] Further, 0.412P+0.6C nb ≤h nb . BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of embodiment 1 of the stud bolt assembly of the present invention;

[0033] Figure 2 It is a tooth profile diagram of a standard metric thread in the prior art;

[0034] Figure 3 The internal thread profile diagram of the protection nut and the broken nut in Embodiment 1 of the stud bolt assembly of the present invention;

[0035] Figure 4 It is a schematic diagram of the internal thread profile of the protection nut and the broken nut and the external thread profile of the stud bolt in Embodiment 1 of the stud bolt assembly of the present invention being simplified into a cantilever beam;

[0036] Figure 5 It is a calibration position diagram of the stud bolt in Embodiment 1 of the stud bolt assembly of the present invention;

[0037] Figure 6 It is a curve diagram showing the change of the average stress at the calibrated position of bolt 1, bolt 2 and the comparison bolt under the same alternating load over time in Example 1 of the stud bolt assembly of the present invention;

[0038] Figure 7 The internal thread profile diagram of the protection nut and the broken nut in Embodiment 2 of the stud bolt assembly of the present invention;

[0039] Figure 8 It is a schematic diagram of the internal thread profile of the protection nut and the broken nut and the external thread profile of the stud bolt in Embodiment 2 of the stud bolt assembly of the present invention being simplified into a cantilever beam;

[0040] Fig. 9 k is C in the embodiment 2 of the stud bolt assembly of the present invention. n and h n Surface graph of the change of

[0041] Fig.10 It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 3 and the comparison bolt under the same alternating load over time in Example 2 of the stud bolt assembly of the present invention;

[0042] Fig.11It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 4 and the comparison bolt under the same alternating load over time in Example 2 of the stud bolt assembly of the present invention;

[0043] Fig.12 It is a curve diagram showing the change of the average stress of bolts 5 to 7 at the calibrated position over time under the same alternating load in Example 3 of the stud bolt assembly of the present invention;

[0044] Fig.13 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0045] Fig.14 The internal thread profile diagram of the protection nut and the broken nut in Embodiment 4 of the stud bolt assembly of the present invention;

[0046] Fig.15 It is a schematic diagram of the internal thread profile of the protection nut and the broken nut and the external thread profile of the stud bolt in Embodiment 4 of the stud bolt assembly of the present invention being simplified into a cantilever beam;

[0047] Fig.16 It is a curve diagram showing the change of the average stress at the calibrated position of bolt 8, bolt 9 and the comparison bolt under the same alternating load over time in Example 4 of the stud bolt assembly of the present invention;

[0048] Fig.17 The internal thread profile diagram of the protection nut and the broken nut in Embodiment 5 of the stud bolt assembly of the present invention;

[0049] Fig.18 It is a schematic diagram of the internal thread profile of the protection nut and the broken nut and the external thread profile of the stud bolt in Embodiment 5 of the stud bolt assembly of the present invention being simplified into a cantilever beam;

[0050] Fig.19 k is C in the embodiment 5 of the stud bolt assembly of the present invention. n and h n Surface graph of the change of

[0051] Fig. 20 It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 10 and the comparison bolt under the same alternating load over time in Example 5 of the stud bolt assembly of the present invention;

[0052] Fig.21 It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 11 and the comparison bolt under the same alternating load over time in Example 5 of the stud bolt assembly of the present invention;

[0053] Fig. 22 The graph is a graph showing the change in average stress over time at the calibrated position of bolts 12 to 14 in Example 6 of the stud bolt assembly of the present invention under the same alternating load. DETAILED DESCRIPTION

[0054] In view of the technical problems existing in the prior art, the basic inventive concept of the present invention is to divide the combination nut used in conjunction with the stud bolt into a protective nut pre-buried in the structure and a breaking nut connected to the end of the stud bolt extending outside the structure, and to design the internal thread parameters of the protective nut and the breaking nut to ensure that the rigidity of the internal thread teeth of the protective nut is smaller, so that when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread of the stud bolt at the protective nut, and making the probability of the stud bolt breaking at the broken nut greater.

[0055] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0056] Embodiment 1 of the stud bolt assembly of the present invention:

[0057] like Figure 1 As shown, the stud bolt assembly includes a stud bolt 1 and a combination nut used in conjunction with the stud bolt 1, the combination nut includes a protective nut 2 for being embedded in the structure and a breaking nut 3 for being connected to one end of the stud bolt 1 extending out of the structure, and the structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt 1 include a protective end external thread 11 connected in conjunction with the protective nut 2 and a breaking end external thread 12 connected in conjunction with the breaking nut 3. In this embodiment, the protective end external thread 11 and the breaking end external thread 12 are both standard metric external threads, and the design parameters of the external threads at both ends are the same. The internal threads of the protective nut 2 and the breaking nut 3 are both metric internal threads used in conjunction with the standard metric external threads, and the internal thread profiles of the protective nut 2 and the breaking nut 3 are both evolved from the tooth profile of the standard metric threads, so the tooth profile of the existing standard metric threads is first introduced below.

[0058] like Figure 2 As shown in the figure, D is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. The crest width of the internal thread is The tooth bottom width is The crest width of the external thread is The tooth bottom width is Since the tooth angle of the internal and external threads is 60°, the tooth height of the internal and external threads can be obtained through geometric calculation. (Right now Figure 2 In ).

[0059] The internal thread profiles of the protection nut and the broken nut are the same, such as Figure 3 As shown, the internal thread profile (solid line in the figure) includes the crest, straight line segment, root and straight line segment connected in sequence, where D is the major diameter of the internal thread, D2 is the middle diameter of the internal thread, D1 is the minor diameter of the internal thread, the profile angle of the internal thread α = 60°, the tooth height The crest width of the internal thread is C n , the tooth bottom width is C n2 , while the root width of the standard metric internal thread is Tooth crest width Therefore, it can be seen from the figure

[0060] Specifically in this embodiment, the minor diameter, middle diameter and major diameter of the internal thread of the protection nut and the broken nut are equal, the tooth angle is 60°, the pitch is P, and the internal thread crest width of the protection nut is defined as C. nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd The internal thread height of the protection nut and the broken nut is equal to the standard metric internal thread height, so At the same time, 0<C nb <C nd <0.25P, and according to the geometric relationship, it can be obtained Therefore, the tooth thickness of the internal threads of the protective nut and the broken nut are both thinned, and the tooth thickness of the internal threads of the protective nut is smaller than the tooth thickness of the internal threads of the broken nut. In this way, the stiffness of the internal threads of the protective nut is smaller than the stiffness of the internal threads of the broken nut, and the bending deflection of the internal threads of the protective nut is greater. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal threads of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external threads of the stud bolt at the protective nut, and improving the fatigue performance of the external threads of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture occurring at the broken nut is greater, which makes it convenient to remove the stud bolt from the structure and facilitate on-site replacement operations.

[0061] In order to further explore the crest width C n A better upper limit value is convenient for subsequent analysis, such as Figure 4 As shown, in this embodiment, the threads of the internal thread and the standard metric external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0062] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0063] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0064] Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0065] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0066] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0067] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0068] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0069] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as:

[0070] In the obtained k about C n In the equation, when 0<C n <0.25P range, k increases with C n increases with the increase of n The larger the value, the greater the bending deflection of the external thread teeth compared to the bending deflection of the internal thread teeth. It can be seen from the equation that when When k is 1, the bending deflection of the internal and external threads is equal. When k < 1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread begins to be smaller than the bending deflection of the internal thread. Therefore, when 0 < C n When ≤0.125P, the bending deflection of the external thread is not greater than that of the internal thread. The internal thread is equivalent to a spring. The internal thread can undergo a larger bending deformation to absorb the inertia force generated by the alternating load, thereby further reducing the stress at the bottom of the external thread under the action of the alternating load, thereby further improving the fatigue performance of the external thread.

[0071] Therefore, we can conclude that C nb and C nd The optimal range is: 0<C nb <C nd ≤0.125P. Within this range, the bending deflection of the inner thread of the protective nut is greater, and the probability of the stud bolt breaking at the broken nut is greater. In addition, for k with respect to C n Equation, due to C nb <C nd , so we can get the ratio k of the external thread deflection of the protection end to the internal thread deflection of the protection nut b The ratio k of the external thread deflection of the broken end to the internal thread deflection of the broken nut d Satisfy: k b <k d .

[0072] In order to verify the superiority of the protection nut and the breaking nut provided in this embodiment, a comparative test was conducted, as shown in Table 1, wherein the external threads of the protection end and the breaking end of bolt 1, bolt 2 and the comparison bolt are all standard metric external threads (for the convenience of description, the present invention also divides the two ends of the comparison bolt into a breaking end and a protection end), and the internal threads of the nuts used at both ends of the comparison bolt are all standard metric internal threads, the major diameters of the internal threads and the external threads are both 36 mm, the pitch P=4 mm, and the other key parameters are shown in Table 1 below.

[0073] Table 1 Key parameters of stud bolts in Example 1

[0074]

[0075] According to the above setting parameters, the general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is imposed on the bolt. Under the same alternating load, the bolt 1, bolt 2 and the comparison bolt are obtained at the calibration position (the bolt has a calibration position at the fracture end and the protection end, and the calibration position is Figure 5 The red dot in the figure is the first position where the bolt's external thread and the nut fit together, which is usually also the position where the stress is most concentrated. Figure 6 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, the average stress of bolt 1 and bolt 2 at each moment is smaller than that of the comparison bolt, and the average stress at the protected end of bolt 1 and bolt 2 at each moment is smaller than the average stress at the fracture end, that is, the fatigue performance of the protected end of the stud bolt is better than that of the fracture end, and when fatigue fracture occurs, the bolt breaks first at the fracture end.

[0076] Embodiment 2 of the stud bolt assembly of the present invention:

[0077] The stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt. The combination nut includes a protective nut for pre-embedded in the structure and a breaking nut for connecting to one end of the stud bolt extending outside the structure. The structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected to the protective nut and a breaking end external thread connected to the breaking nut. The protective end external thread and the breaking end external thread are still standard metric external threads, and the design parameters of the external threads at both ends are the same. The internal threads of the protective nut and the breaking nut are both metric internal threads used in conjunction with the standard metric external threads. The internal thread profiles of the protective nut and the breaking nut are the same, and both are evolved from the tooth profile of the standard metric thread.

[0078] like Figure 7 As shown, the internal thread profile of the protective nut and the broken nut (solid line in the figure) includes the crest, straight line segment, root and straight line segment connected in sequence, where D1 is the internal thread minor diameter, the internal thread profile angle α = 60°, and the tooth height is h n , crest width is C n , the tooth bottom width is C n2 , while the major diameter of the standard metric internal thread is D, the middle diameter is D2, and the root width is Tooth crest width Tooth height Therefore, it can be seen from the figure

[0079] Specifically in this embodiment, the internal thread minor diameters of the protection nut and the broken nut are equal, the tooth angles are both 60°, and the pitches are both P. The internal thread crest width of the protection nut is defined as C.nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd , then 0<C nb <C nd <0.25P, and according to the geometric relationship, it can be obtained h nd and h nb satisfy: That is h nd and h nb Both are greater than the tooth height of the standard metric internal thread and less than the tooth height at the vertex of the original triangle, ensuring that the tooth profile with a pitch of P and a tooth profile angle α of 60° can still exist. nb >h nd Therefore, in this embodiment, the tooth thickness of the internal thread teeth of the protective nut and the broken nut are both thinned and the tooth height is increased, and the tooth thickness of the internal thread teeth of the protective nut is less than the tooth thickness of the internal thread teeth of the broken nut, and the tooth height of the internal thread teeth of the protective nut is greater than the tooth height of the internal thread teeth of the broken nut. In this way, the rigidity of the internal thread teeth of the protective nut is less than the rigidity of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is greater. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread teeth of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture occurring at the broken nut is greater, and the stud bolt can be easily removed from the structure, which is convenient for on-site replacement operations.

[0080] In order to further explore the optimal range and facilitate subsequent analysis, Figure 8 As shown, in this embodiment, the threads of the internal thread and the standard metric external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0081] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0082] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0083] Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0084] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0085] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is where h w is the tooth height of the standard metric external thread, i.e. h w =h0, then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q w for:

[0086] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0087] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0088] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as: This formula can be transformed into:

[0089] According to k and C n and h n The equation plots k as a function of C n and h n Surfaces such as Fig. 9 As shown. When k≤1, That is: 0.464P+0.619C n ≤h n , where 0 <C n <0.25P. That is, Fig. 9 In the curved surface below the k=1 contour line, the bending deflection of the external thread teeth is not greater than that of the internal thread teeth. The bending deflection of the internal thread teeth is larger, and the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, so that the inertia force borne by the external thread teeth is lower, and the fatigue performance of the external thread is better.

[0090] For the protection nut, its C nb and h nb Satisfaction: 0.464P+0.619C nb ≤h nb , C of the broken nut nd and h nd Satisfaction: 0.464P+0.619C nd ≤h nd . And the ratio of the deflection of the external thread of the protection end to the deflection of the internal thread of the protection nut The ratio of the deflection of the external thread of the broken end to the deflection of the internal thread of the broken nut Due to C nb <C nd , and h nb >h nd , so we can get k b <k d .

[0091] In order to verify the superiority of the protection nut and the breaking nut provided in this embodiment, a comparative test was conducted, as shown in Table 2, wherein the external threads of the protection end and the breaking end of the bolt 3, the bolt 4 and the comparative bolt are all standard metric external threads, the major diameter of the external threads is 36 mm, the internal threads of the nuts used at both ends of the comparative bolt are all standard metric internal threads, the pitch P of all external threads and internal threads is 4 mm, and the other key parameters are shown in Table 2 below.

[0092] Table 2 Key parameters of stud bolts in Example 2

[0093]

[0094] According to the above setting parameters, the general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt, and the average stress variation with time curves of bolt 3 and the comparison bolt, and bolt 4 and the comparison bolt at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load are obtained.

[0095] The ratio k of the external thread deflection of the broken end of bolt 3 to the internal thread deflection of the broken nut d is 1.179, the ratio of the external thread deflection of the protection end to the internal thread deflection of the protection nut is k b is 0.346, Fig.10 It can be seen that the average stress at the calibrated position of the fracture end of bolt 3 is slightly smaller than the average stress at the calibrated position of the comparison bolt, and the average stress at the calibrated position of the protection end is smaller than the average stress at the calibrated position of the comparison bolt. This shows that the fatigue performance of bolt 3 is better, and the average stress at the protection end of bolt 3 is smaller than the average stress at the fracture end. The fatigue performance of the protection end is better. When fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0096] The ratio k of the external thread deflection of the broken end of bolt 4 to the internal thread deflection of the broken nut d The ratio k of the external thread deflection of the protection end to the internal thread deflection of the protection nut is 0.151. b is 0.076, Fig.11 It can be seen that the average stress at the calibrated position of the fracture end and the protection end of bolt 4 is less than the average stress at the calibrated position of the comparison bolt, which shows that the fatigue performance of bolt 4 is better. At the same time, since the average stress at the protection end of bolt 4 is less than the average stress at the fracture end, the fatigue performance of the protection end is better. When fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0097] Embodiment 3 of the stud bolt assembly of the present invention:

[0098] The stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt. The combination nut includes a protective nut embedded in the structure and a breaking nut connected to one end of the stud bolt extending outside the structure. The structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected to the protective nut and a breaking end external thread connected to the breaking nut. The protective end external thread and the breaking end external thread are still standard metric external threads, and the design parameters of the external threads at both ends are the same. The internal thread of the breaking nut is a standard metric internal thread, and the internal thread of the protective nut is an improved metric internal thread used in conjunction with the standard metric external thread. The internal thread profile of the protective nut is evolved from the standard metric thread profile. The internal thread profile lines of the protective nut and the breaking nut still include a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence.

[0099] The internal thread diameters of the protection nut and the broken nut are equal, the tooth angle is 60°, and the pitch is P. The internal thread crest width of the protection nut is defined as C. nb , the tooth bottom width is C nb2 , tooth height is h nb, the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd Since the internal thread of the broken nut is a standard metric internal thread, And 0<C nb <0.25P, and according to the geometric relationship, it can be obtained at the same time h nb The tooth height is greater than that of the standard metric internal thread and less than the tooth height at the vertex of the original triangle, ensuring that the tooth profile with a pitch of P and a tooth angle α of 60° can still exist.

[0100] Therefore, in this embodiment, the tooth thickness of the internal thread teeth of the protective nut is thinned and the tooth height is increased, while the broken nut is a standard metric thread. Therefore, the tooth thickness of the internal thread teeth of the protective nut is smaller than the tooth thickness of the internal thread teeth of the broken nut, and the tooth height of the internal thread teeth of the protective nut is larger than the tooth height of the internal thread teeth of the broken nut. In this way, the stiffness of the internal thread teeth of the protective nut is smaller than the stiffness of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread teeth of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, and the stud bolt can be conveniently removed from the structure, thereby facilitating on-site replacement operations.

[0101] Further, refer to Figure 8 The internal thread of the protective nut and the standard metric external thread are simplified into a set of interacting rectangular cantilever beams. The internal and external thread action point Q is the midpoint of the overlap area of ​​the internal and external thread teeth. The tooth width of the simplified cantilever beam of the external thread teeth is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0102] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0103] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height. Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified is 内 C n1, the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are: According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0104] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is where h w is the tooth height of the standard metric external thread, i.e. h w =h0, then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q w for:

[0105] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0106] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0107] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as: This formula can be transformed into: When k≤1, That is: 0.464P+0.619C n ≤h n , the bending deflection of the external thread teeth is not greater than the bending deflection of the internal thread teeth.

[0108] For the protection nut, the ratio of the external thread deflection of the stud bolt protection end to the internal thread deflection of the protection nut When C nb and h nb Satisfaction: 0.464P+0.619C nb ≤h nbWhen the deflection of the external thread teeth at the protective end of the stud bolt is not greater than the deflection of the internal thread teeth of the protective nut, the bending deflection of the internal thread teeth of the protective nut is larger, and a larger bending deformation can occur to absorb the inertia force generated by the alternating load, so that the inertia force borne by the external thread teeth is lower, and the fatigue performance of the external thread is better.

[0109] The following provides a comparative test. As shown in Table 3, the external threads of the protection ends and broken ends of bolts 5 to 7 are all standard metric external threads, and the major diameter of the external threads is 36 mm. The internal threads of the broken nuts are standard metric internal threads, and the major diameter of the internal threads of the broken nuts is 36 mm. The pitch of all external and internal threads is P = 4 mm. The other key parameters are shown in Table 3 below.

[0110] Table 3 Key parameters of stud bolts in Example 3

[0111]

[0112] According to the above setting parameters, the dynamic analysis of the internal and external threads is performed using general finite element analysis software, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt, and the average stress variation curve of bolts 5 to 7 at the calibrated position (the calibrated position is the same as that in Example 1) under the same alternating load is obtained. Fig.12 As shown in the figure, the average stress at the marked position of the fracture end of the three stud bolts is equal and greater than the average stress at the marked position of the protection end. Table 4 shows the stress amplitudes of the three stud bolts (maximum stress minus minimum stress) and the stress amplitude difference between the fracture end and the protection end. It can be seen that the stress amplitudes of the fracture ends of the three stud bolts are greater than the stress amplitudes of the protection end, that is, the fatigue performance of the protection end of the stud bolt is better than that of the fracture end. When fatigue fracture occurs, the bolt breaks first at the fracture end.

[0113] Table 4 Stress amplitude and amplitude difference of stud bolts in Example 3

[0114] Bolt 5 Bolt 6 Bolt 7 Broken end 124.955Mpa 124.943Mpa 123.942Mpa Protection end 124.569Mpa 123.199Mpa 121.962Mpa Amplitude difference 0.386Mpa 1.744Mpa 2.98Mpa

[0115] Embodiment 4 of the stud bolt assembly of the present invention:

[0116] The stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt. The combination nut includes a protective nut embedded in the structure and a breaking nut connected to one end of the stud bolt extending outside the structure. The structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected to the protective nut and a breaking end external thread connected to the breaking nut. Both the protective end external thread and the breaking end external thread are standard MJ external threads, and the design parameters of the external threads at both ends are the same. Both the internal threads of the protective nut and the breaking nut are MJ internal threads used in conjunction with the standard MJ external threads. The internal thread profiles of the protective nut and the breaking nut are the same, and both are evolved from the tooth profile of the standard MJ thread. Therefore, the tooth profile of the existing standard MJ thread is first introduced below.

[0117] like Fig.13 As shown in the figure, D is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. Unlike metric threads, the crest width of MJ internal threads is The tooth bottom width is The crest width of the MJ external thread is The tooth bottom width is Since the tooth angles of the MJ internal and external threads are both 60°, the tooth heights of the MJ internal and external threads can be obtained through geometric calculations as follows: (Right now Fig.13 In ).

[0118] The internal thread profile of the protective nut and the broken nut is as follows Fig.14 As shown, the internal thread profile (solid line in the figure) still includes the crest, straight line segment, root and straight line segment connected in sequence, where D is the major diameter of the internal thread, D2 is the middle diameter of the internal thread, D1 is the minor diameter of the internal thread, the profile angle of the internal thread α = 60°, the tooth height The crest width of the internal thread is C n , the tooth bottom width is C n2 , while the standard MJ internal thread root width is Tooth crest width Therefore, it can be seen from the figure

[0119] Specifically in this embodiment, the minor diameter, middle diameter and major diameter of the internal thread of the protection nut and the broken nut are equal, the tooth angle is 60°, the pitch is P, and the internal thread crest width of the protection nut is defined as C. nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is Cnd , the tooth bottom width is C nd2 , tooth height is h nd The internal thread height of the protection nut and the broken nut is equal to the standard MJ internal thread height. at the same time, And according to the geometric relationship, we can find Therefore, the tooth thickness of the internal threads of the protective nut and the broken nut are both thinned, and the tooth thickness of the internal threads of the protective nut is smaller than the tooth thickness of the internal threads of the broken nut. In this way, the stiffness of the internal threads of the protective nut is smaller than the stiffness of the internal threads of the broken nut, and the bending deflection of the internal threads of the protective nut is greater. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal threads of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external threads of the stud bolt at the protective nut, and improving the fatigue performance of the external threads of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture occurring at the broken nut is greater, which makes it convenient to remove the stud bolt from the structure and facilitate on-site replacement operations.

[0120] In order to further explore the crest width C n A better upper limit value is convenient for subsequent analysis, such as Fig.15 As shown, in this embodiment, the threads of the internal thread and the standard MJ external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0121] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0122] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height. Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified is 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are: According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the action point, l is the distance between the action point and the support position, and E is the elastic modulus of the cantilever beam.

[0123] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0124] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0125] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0126] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as:

[0127] In the obtained k about C n In the equation, In the range, k increases with C n increases with the increase of n The larger the value, the greater the bending deflection of the external thread teeth compared to the bending deflection of the internal thread teeth. It can be seen from the equation that when When k is 1, the bending deflection of the internal and external threads is equal. When k < 1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread begins to be smaller than the bending deflection of the internal thread. Therefore, when 0 < C n When ≤0.125P, the bending deflection of the external thread is not greater than that of the internal thread, and the internal thread can undergo a larger bending deformation to absorb the inertia force generated by the alternating load, thereby further reducing the stress at the bottom of the external thread under the action of the alternating load, thereby further improving the fatigue performance of the external thread.

[0128] Therefore, we can conclude that C nb and C nd The optimal range is: 0<C nb <C nd≤0.125P. Within this range, the bending deflection of the inner thread of the protective nut is greater, and the probability of the stud bolt breaking at the broken nut is greater. In addition, for k with respect to C n Equation, due to C nb <C nd , so we can get the ratio k of the external thread deflection of the protection end to the internal thread deflection of the protection nut b The ratio k of the external thread deflection of the broken end to the internal thread deflection of the broken nut d Satisfy: k b <k d .

[0129] The following provides a comparative test, as shown in Table 5, in which the external threads of the protection end and the broken end of bolt 8, bolt 9 and the comparative bolt are all standard MJ external threads, the internal threads of the nuts used at both ends of the comparative bolt are all standard MJ internal threads, the major diameters of the internal and external threads are both 36 mm, the pitch P = 4 mm, and the other key parameters are shown in Table 5 below.

[0130] Table 5 Key parameters of stud bolts in Example 4

[0131]

[0132] According to the above setting parameters, the dynamic analysis of the internal and external threads is performed using general finite element analysis software, that is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is imposed on the bolt, and the average stress variation curve of bolt 8, bolt 9 and the comparison bolt at the calibrated position (the calibrated position is the same as that of Example 1) under the same alternating load is obtained. Fig.16 As shown, the average stress at both ends of the comparison bolt is equal at each moment, the average stress at each moment of bolt 8 and bolt 9 is less than that of the comparison bolt, and the average stress at the protection end of bolt 8 and bolt 9 is less than the average stress at the fracture end at each moment, that is, the fatigue performance of the protection end of the stud bolt is better than that of the fracture end, and when fatigue fracture occurs, the bolt breaks first at the fracture end.

[0133] Embodiment 5 of the stud bolt assembly of the present invention:

[0134] The stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt. The combination nut includes a protective nut embedded in the structure and a breaking nut connected to one end of the stud bolt extending outside the structure. The structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected to the protective nut and a breaking end external thread connected to the breaking nut. The protective end external thread and the breaking end external thread are still standard MJ external threads, and the design parameters of the external threads at both ends are the same. The internal threads of the protective nut and the breaking nut are both MJ internal threads used in conjunction with the standard MJ external threads. The internal thread profiles of the protective nut and the breaking nut are the same, and both are evolved from the standard MJ thread profile.

[0135] like Fig.17 As shown, the internal thread profile of the protective nut and the broken nut (solid line in the figure) includes the crest, straight line segment, root and straight line segment connected in sequence, where D1 is the internal thread minor diameter, the internal thread profile angle α = 60°, and the tooth height is h n , crest width is C n , the tooth bottom width is C n2 , while the standard MJ internal thread has a major diameter of D, a mid diameter of D2, and a root width of Tooth crest width Tooth height Therefore, it can be seen from the figure

[0136] Specifically in this embodiment, the internal thread minor diameters of the protection nut and the broken nut are equal, the tooth angles are both 60°, and the pitches are both P. The internal thread crest width of the protection nut is defined as C. nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd ,but And according to the geometric relationship, we can find h nd and h nb satisfy: That is h nd and h nb Both are greater than the tooth height of the standard MJ internal thread and less than the tooth height at the vertex of the original triangle, ensuring that the tooth profile with a pitch of P and a tooth profile angle α of 60° can still exist. nb >h ndTherefore, in this embodiment, the tooth thickness of the internal thread teeth of the protective nut and the broken nut are both thinned and the tooth height is increased, and the tooth thickness of the internal thread teeth of the protective nut is less than the tooth thickness of the internal thread teeth of the broken nut, and the tooth height of the internal thread teeth of the protective nut is greater than the tooth height of the internal thread teeth of the broken nut. In this way, the rigidity of the internal thread teeth of the protective nut is less than the rigidity of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is greater. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread teeth of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture occurring at the broken nut is greater, and the stud bolt can be easily removed from the structure, which is convenient for on-site replacement operations.

[0137] In order to further explore the optimal range and facilitate subsequent analysis, Fig.18 As shown, in this embodiment, the threads of the internal thread and the standard MJ external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0138] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0139] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height. Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified is 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are: According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0140] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0141] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0142] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0143] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as: This formula can be transformed into:

[0144] According to k and C n and h n The equation plots k as a function of C n and h n Surfaces such as Fig.19 As shown. When k≤1, That is: 0.412P+0.6C n ≤h n ,in That is to say, Fig.19 In the curved surface below the k=1 contour line, the bending deflection of the external thread teeth is not greater than that of the internal thread teeth. The bending deflection of the internal thread teeth is larger, and the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, so that the inertia force borne by the external thread teeth is lower, and the fatigue performance of the external thread is better.

[0145] For the protection nut, its C nb and h nb Satisfaction: 0.412P+0.6C nb ≤h nb , C of the broken nut nd and h nd Satisfaction: 0.412P+0.6C nd ≤h nd . And the ratio of the deflection of the external thread of the protection end to the deflection of the internal thread of the protection nut The ratio of the deflection of the external thread of the broken end to the deflection of the internal thread of the broken nut Due to C nb <C nd , and h nb >h nd , so we can get k b <k d .

[0146] The following provides a comparative test, as shown in Table 6, in which the external threads of the protection end and the broken end of bolt 10, bolt 11 and the comparative bolt are all standard MJ external threads, the major diameter of the external threads is 36 mm, the internal threads of the nuts used at both ends of the comparative bolts are all standard MJ internal threads, the pitch of all external threads and internal threads is P = 4 mm, and the other key parameters are shown in Table 6 below.

[0147] Table 6 Key parameters of stud bolts in Example 5

[0148]

[0149] According to the above setting parameters, the general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt, and the average stress variation with time curves of bolt 10 and the comparison bolt, and bolt 11 and the comparison bolt at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load are obtained.

[0150] The ratio k of the external thread deflection of the broken end of bolt 10 to the internal thread deflection of the broken nut d The ratio k of the external thread deflection of the protection end to the internal thread deflection of the protection nut is 2.51. b is 0.358, Fig. 20 It can be seen that the average stresses at the calibrated positions of the fracture end and the protection end of bolt 10 are both smaller than the average stress at the calibrated position of the comparison bolt, which indicates that the fatigue performance of bolt 10 is better, and the average stress at the protection end of bolt 10 is smaller than the average stress at the fracture end, so the fatigue performance of the protection end is better. When fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0151] The ratio k of the external thread deflection of the broken end of bolt 11 to the internal thread deflection of the broken nut d The ratio k of the external thread deflection of the protection end to the internal thread deflection of the protection nut is 0.182. b is 0.092, Fig.21 It can be seen that the average stress at the calibrated position of the fracture end and the protection end of bolt 11 is less than the average stress at the calibrated position of the comparison bolt, which shows that the fatigue performance of bolt 11 is better. At the same time, since the average stress at the protection end of bolt 11 is less than the average stress at the fracture end, the fatigue performance of the protection end is better. When fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0152] Embodiment 6 of the stud bolt assembly of the present invention:

[0153] The stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt. The combination nut includes a protective nut embedded in the structure and a breaking nut connected to one end of the stud bolt extending outside the structure. The structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected to the protective nut and a breaking end external thread connected to the breaking nut. The protective end external thread and the breaking end external thread are still standard MJ external threads, and the design parameters of the threads are the same. The internal thread of the breaking nut is a standard MJ internal thread, and the internal thread of the protective nut is an improved MJ internal thread used in conjunction with the standard MJ external thread. The internal thread profile of the protective nut is evolved from the standard MJ thread profile. The internal thread profile lines of the protective nut and the breaking nut still include a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence.

[0154] The internal thread diameters of the protection nut and the broken nut are equal, the tooth angle is 60°, and the pitch is P. The internal thread crest width of the protection nut is defined as C. nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd Since the internal thread of the broken nut is a standard MJ internal thread, and And according to the geometric relationship, we can find at the same time h nb The tooth height is larger than the standard MJ internal thread and smaller than the tooth height at the vertex of the original triangle, ensuring that the tooth profile with a pitch of P and a tooth angle α of 60° can still exist.

[0155] Therefore, in this embodiment, the tooth thickness of the internal thread teeth of the protective nut is thinned and the tooth height is increased, and the broken nut is a standard MJ thread, so the tooth thickness of the internal thread teeth of the protective nut is smaller than the tooth thickness of the internal thread teeth of the broken nut, and the tooth height of the internal thread teeth of the protective nut is larger than the tooth height of the internal thread teeth of the broken nut, so that the stiffness of the internal thread teeth of the protective nut is smaller than the stiffness of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread teeth of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, and the stud bolt can be conveniently removed from the structure, facilitating on-site replacement operations.

[0156] Further, refer to Fig.18 The internal thread of the protective nut and the standard MJ external thread are simplified into a set of interacting rectangular cantilever beams. The internal and external thread action point Q is the midpoint of the overlap area of ​​the internal and external thread teeth. The tooth width of the simplified cantilever beam of the external thread teeth is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0157] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0158] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height. Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified is 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are: According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the action point, l is the distance between the action point and the support position, and E is the elastic modulus of the cantilever beam.

[0159] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0160] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0161] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0162] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as: This formula can be transformed into: When k≤1, That is: 0.412P+0.6C n ≤h n , the bending deflection of the external thread teeth is not greater than the bending deflection of the internal thread teeth.

[0163] For the protection nut, the ratio of the external thread deflection of the stud bolt protection end to the internal thread deflection of the protection nut When C nb and h nb Satisfaction: 0.412P+0.6C nb ≤h nb When the deflection of the external thread teeth at the protective end of the stud bolt is not greater than the deflection of the internal thread teeth of the protective nut, the bending deflection of the internal thread teeth of the protective nut is larger, and a larger bending deformation can occur to absorb the inertia force generated by the alternating load, so that the inertia force borne by the external thread teeth is lower, and the fatigue performance of the external thread is better.

[0164] The following provides a comparative test. As shown in Table 7, the external threads of the protection ends and the broken ends of bolts 12 to 14 are all standard MJ external threads, and the major diameter of the external threads is 36 mm. The internal threads of the broken nuts are standard MJ internal threads, and the major diameter of the internal threads of the broken nuts is 36 mm. The pitch of all external and internal threads is P = 4 mm. The other key parameters are shown in Table 7 below.

[0165] Table 7 Key parameters of stud bolts in Example 6

[0166]

[0167]

[0168] According to the above setting parameters, a general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is imposed on the bolt, and the average stress variation curve of the bolts 12 to 14 at the calibrated positions (the calibrated positions are the same as those in Example 1) under the same alternating load is obtained. Fig. 22 As shown in the figure, the average stress at the marked position of the fracture end of the three stud bolts is equal and greater than the average stress at the marked position of the protection end. Table 8 shows the stress amplitudes of the three stud bolts (maximum stress minus minimum stress) and the stress amplitude difference between the fracture end and the protection end. It can be seen that the stress amplitudes of the fracture ends of the three stud bolts are greater than the stress amplitudes of the protection end, that is, the fatigue performance of the protection end of the stud bolt is better than that of the fracture end. When fatigue fracture occurs, the bolt breaks first at the fracture end.

[0169] Table 8 Stress amplitude and amplitude difference of stud bolts in Example 6

[0170] Bolt 12 Bolt 13 Bolt 14 Broken end 123.873Mpa 123.874Mpa 123.874Mpa Protection end 123.743Mpa 121.841Mpa 119.918Mpa Amplitude difference 0.13Mpa 2.033Mpa 3.956Mpa

[0171] Embodiment 7 of the stud bolt assembly of the present invention:

[0172] Different from Example 6, At this time, the tooth thickness of the internal thread of the protective nut is only reduced. Although the tooth height is not increased, compared with the prior art, the stiffness of the internal thread of the protective nut is still less than that of the internal thread of the broken nut, and the bending deflection of the internal thread of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture occurring at the broken nut is higher.

[0173] At the same time, due to Therefore, referring to Example 4, it can be seen that the ratio of the external thread deflection to the internal thread deflection is When k≤1, C n ≤0.125P, the bending deflection of the external thread is not greater than the bending deflection of the internal thread. Combined with the protection nut, the ratio of the external thread deflection of the protection end to the internal thread deflection of the protection nut When k b When ≤1, C nb ≤0.125P. Within this range, the bending deflection of the inner thread teeth of the protective nut is greater, and the probability of the stud bolt breaking at the broken nut is greater.

[0174] Embodiment 8 of the stud bolt assembly of the present invention:

[0175] Different from Example 3, At this time, the tooth thickness of the internal thread of the protective nut is only reduced. Although the tooth height is not increased, compared with the prior art, the stiffness of the internal thread of the protective nut is still less than that of the internal thread of the broken nut, and the bending deflection of the internal thread of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture occurring at the broken nut is higher.

[0176] At the same time, due to Therefore, referring to Example 1, it can be seen that the ratio of the external thread deflection to the internal thread deflection is When k≤1, C n ≤0.125P, the bending deflection of the external thread is not greater than the bending deflection of the internal thread. Combined with the protection nut, the ratio of the external thread deflection of the protection end to the internal thread deflection of the protection nut When k b When ≤1, C nb ≤0.125P. Within this range, the bending deflection of the inner thread teeth of the protective nut is greater, and the probability of the stud bolt breaking at the broken nut is greater.

[0177] The embodiment of the combination nut for stud bolts in the present invention is as follows: the specific structure of the combination nut for stud bolts is the same as the combination nut in any embodiment of the stud bolt assembly described above, and will not be repeated here.

[0178] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the protection scope of the present invention.

Claims

1. A combination nut for a stud bolt, characterized in that: It includes a protective nut used for pre-embedded in the structure and a breaking nut used for connecting with the end of the stud bolt extending outside the structure. The internal threads of the protective nut and the breaking nut are both metric threads or MJ threads, and the tooth profile of the internal thread includes the top, straight line segment, bottom and straight line segment connected in sequence. The minor diameter of the internal thread of the protective nut and the breaking nut is equal, the tooth angle is 60°, the pitch is P, and the top width of the internal thread of the protective nut is defined as C. nb , the tooth bottom width is C nb2 , tooth height is h nb , the internal thread crest width of the broken nut is C nd , the tooth bottom width is C nd2 , tooth height is h nd , then 0<C nb <C nd , 2. The combination nut for stud bolts according to claim 1, characterized in that: C nd <C0, C0 is the crest width of standard metric internal thread or MJ internal thread.

3. The combination nut for stud bolts according to claim 2, characterized in that: The internal threads of the protection nut and the breaking nut are metric internal threads for use with standard metric external threads. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C nb <C nd ≤0.125P.

4. The combination nut for stud bolts according to claim 2, characterized in that: The internal threads of the protection nut and the breaking nut are both MJ internal threads for use with standard MJ external threads. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C nb <C nd ≤0.125P.

5. The combination nut for stud bolts according to claim 2, characterized in that: h nb >h nd , h0 is the tooth height of standard metric internal thread or MJ internal thread.

6. The combination nut for stud bolts according to claim 5, characterized in that: The internal threads of the protection nut and the breaking nut are metric internal threads for use with standard metric external threads. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, and 0.464P+0.619C is obtained. nb ≤h nb , 0.464P+0.619C nd ≤h nd .

7. The combination nut for stud bolts according to claim 5, characterized in that: The internal threads of the protection nut and the breaking nut are both MJ internal threads for use with standard MJ external threads. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, and 0.412P+0.6C is obtained. nb ≤h nb , 0.412P+0.6C nd ≤h nd .

8. The combination nut for stud bolts according to claim 1, characterized in that: The internal thread of the broken nut is a standard metric internal thread, and the internal thread of the protection nut is an improved metric internal thread for use with a standard metric external thread. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C nb ≤0.125P.

9. The combination nut for stud bolts according to claim 8, characterized in that: 0.464P+0.619C nb ≤h nb 。 10. The combination nut for stud bolts according to claim 1, characterized in that: The internal thread of the broken nut is a standard MJ internal thread, and the internal thread of the protection nut is an improved MJ internal thread used in conjunction with the standard MJ external thread. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C nb ≤0.125P.

11. The combination nut for stud bolts according to claim 10, characterized in that: 0.412P+0.6C nb ≤h nb 。 12. A stud bolt assembly, comprising a stud bolt and a combination nut used in conjunction with the stud bolt, characterized in that: The external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same. The combination nut is the combination nut for the stud bolt as described in any one of claims 1 to 11.

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