Stud bolt and stud bolt assembly

Abstract

The invention provides a double-end bolt and a double-end bolt assembly, and belongs to the technical field of bolt connection. The external threads at the two ends of the double-end bolt comprise protection end external threads used for being connected with embedded nuts in a structural body in a matched mode and fracture end external threads used for being connected with fastening nuts outside the structural body in a matched mode, and the thread angle, the thread pitch and the small diameter of the protection end external threads are equal to those of the fracture end external threads. The major diameter of the protection end external thread is smaller than that of the fracture end external thread. The thread height of the protection end external thread is smaller than that of the fracture end external thread, so that the thread tooth rigidity of the protection end external thread can be improved, the fatigue performance of the protection end external thread when the protection end external thread bears alternating loads is improved, the fracture position of the stud is located on the fracture end external thread, and therefore when the stud is fractured, the stud can be conveniently detached from a structural body, and the service life of the stud is prolonged. And on-site replacement operation is facilitated.

Description

Technical Field

[0001] The invention relates to 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 stud bolt to solve the problem that the fracture position of the existing stud bolt cannot be predicted, resulting in that when the fracture position of the stud bolt is located at the matching position with the embedded nut, the broken bolt head is located inside the structure and is very difficult to remove, which brings great trouble to the on-site replacement operation; the object of the present invention is also to provide a stud bolt assembly to solve the above problem.

[0005] To achieve the above purpose, the stud bolt in the present invention adopts the following technical solution:

[0006] A stud bolt, the external threads at both ends of the stud bolt include a protective end external thread for cooperating with an embedded nut in a structure and a broken end external thread for cooperating with a fastening nut outside the structure, the protective end external thread and the broken end external thread are both metric threads or MJ threads, and the tooth angle, pitch and minor diameter of the external threads are respectively equal, and the major diameter of the protective end external thread is smaller than the major diameter of the broken end external thread.

[0007] The beneficial effect of the above technical solution is that: the present invention is a pioneering invention, the external threads at both ends of the stud bolt of the present invention include a protective end external thread and a broken end external thread, the protective end external thread is connected with the embedded nut in the structure, and the protective measures are provided to ensure that it will not break; the broken end external thread is connected with the fastening nut outside the structure, and is a thread that is expected to break. The specific measures are that the protective end external thread and the broken end external thread are both metric threads or MJ threads, and the tooth angle, pitch and minor diameter of the external thread are respectively equal, but the major diameter of the protective end external thread is smaller than the major diameter of the broken end external thread, which is equivalent to the tooth height of the protective end external thread being smaller than the tooth height of the broken end external thread, so that the thread stiffness of the protective end external thread can be improved, and its fatigue performance when subjected to alternating loads can be improved, so that the fracture position of the stud bolt is on the broken end external thread, and then when the stud bolt breaks, it is easy to remove the stud bolt from the structure, which is convenient for on-site replacement operations.

[0008] Furthermore, the thread height of the external thread at the fracture end is defined as h wd , the tooth height of the external thread at the protection end is h wb According to the safety of the external thread of the protection end and the embedded nut, and the safety of the external thread of the broken end and the fastening nut, the effective overlap rate of the thread between the external thread of the protection end and the embedded nut, and between the external thread of the broken end and the fastening nut is not less than 25%, and h is determined. wb The range is h wd The range is At the same time, h wb <h wd , where h ny h is the standard thread height of the internal thread of the embedded nut nj h is the standard thread height of the internal thread of the fastening nut. ny =h nj .

[0009] Furthermore, the external thread at the protection end and the external thread at the fracture end are both metric threads, the pitch of the external thread at the protection end and the fracture end is P, the thread bottom width is 0.25P, the thread angle is 60°, and the major diameter of the external thread at the protection end is d b , crest width is C wb , the major diameter of the external thread at the fracture end is d d , crest width is C wd, according to the crest width C wb and the tooth height h wb The geometric relationship satisfied The major diameter of the external thread at the protection end The crest width C wd and the tooth height h wd The geometric relationship satisfied The major diameter of the external thread at the fracture end It can be calculated that: D - 0.812P ≤ d b < d d < D, where D is the major diameter of the internal threads of the embedded nut and the fastening nut.

[0010] Furthermore, based on the fact that the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the protection end is not greater than one-tenth of the bending deflection of the rectangular cantilever beam simplified from the thread of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the fracture end is not greater than one-tenth of the bending deflection of the rectangular cantilever beam simplified from the thread of the internal thread of the fastening nut, it is obtained that D - 0.812P ≤ d b < d d ≤ D - 0.083P.

[0011] Furthermore, based on the fact that the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the protection end is not greater than one-tenth of the bending deflection of the rectangular cantilever beam simplified from the thread of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the fracture end is not greater than one-tenth of the bending deflection of the rectangular cantilever beam simplified from the thread of the internal thread of the fastening nut, it is obtained that D - 0.812P ≤ d b < d d ≤ D - 0.332P.

[0012] Furthermore, both the external thread at the protection end and the external thread at the fracture end are MJ threads, the pitch of the external thread at the protection end and the external thread at the fracture end is P, and the root width is The thread angle is 60°, the major diameter of the external thread at the protection end is d b and the crest width is C wb , the major diameter of the external thread at the fracture end is d d and the crest width is C wd , according to the crest width C wb and the tooth height h wb The geometric relationship satisfied The major diameter of the external thread at the protection end The crest width C wd and the tooth height h wd The geometric relationship satisfied The major diameter of the external thread at the fracture end It can be calculated that: D - 0.731P ≤ d b < d d<D, where D is the major diameter of the internal threads of the embedded nut and the fastening nut.

[0013] Further, based on the fact that the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the protection end is not greater than that of the rectangular cantilever beam simplified from the thread of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the fracture end is not greater than that of the rectangular cantilever beam simplified from the thread of the internal thread of the fastening nut, it is obtained that D - 0.731P ≤ d b <d d ≤ D - 0.118P.

[0014] Further, based on the fact that the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the protection end is not greater than one-tenth of that of the rectangular cantilever beam simplified from the thread of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread at the fracture end is not greater than one-tenth of that of the rectangular cantilever beam simplified from the thread of the internal thread of the fastening nut, it is obtained that D - 0.731P ≤ d b <d d ≤ D - 0.346P.

[0015] Further, the external thread at the fracture end is a standard metric thread or an MJ thread, the external thread at the protection end is an improved metric thread or an MJ thread, and the tooth height of the external thread at the protection end is h wb , based on the safety of the fit between the external thread at the protection end and the embedded nut, ensuring that the effective coincidence rate of the threads between the external thread at the protection end and the embedded nut is not less than 25%, the range of h wb is where h ny is the standard tooth height of the internal thread of the embedded nut.

[0016] To achieve the above object, the following technical solution is adopted for the double-headed bolt assembly in the present invention:

[0017] A double-headed bolt assembly includes a double-headed bolt, an embedded nut used in cooperation with the double-headed bolt and embedded in a structure, and a fastening nut arranged outside the structure. The external threads at both ends of the double-headed bolt include a protection-end external thread for cooperating and connecting with the embedded nut inside the structure and a fracture-end external thread for cooperating and connecting with the fastening nut outside the structure. Both the protection-end external thread and the fracture-end external thread are metric threads or MJ threads, and the thread profile angle, pitch, and minor diameter of the external threads are respectively equal. The major diameter of the protection-end external thread is smaller than that of the fracture-end external thread.

[0018] The beneficial effect of the above technical solution is that: the present invention belongs to an improved invention creation, and further limits the structure of the stud bolt. The external threads at both ends of the stud bolt include a protective end external thread and a broken end external thread. The protective end external thread is connected with the embedded nut in the structure, and the protective measures are set to ensure that it will not break; the broken end external thread is connected with the fastening nut outside the structure, and is a thread that is expected to break. The specific measures are that the protective end external thread and the broken end external thread are both metric threads or MJ threads, and the tooth angle, pitch and minor diameter of the external thread are respectively equal, but the major diameter of the protective end external thread is smaller than the major diameter of the broken end external thread, which is equivalent to the tooth height of the protective end external thread being smaller than the tooth height of the broken end external thread. Therefore, the thread stiffness of the protective end external thread can be improved, and its fatigue performance when subjected to alternating loads can be improved, so that the fracture position of the stud bolt is on the broken end external thread, and then when the stud bolt breaks, it is easy to remove the stud bolt from the structure, which is convenient for on-site replacement operations.

[0019] Furthermore, the thread height of the external thread at the fracture end is defined as h wd , the tooth height of the external thread at the protection end is h wb According to the safety of the external thread of the protection end and the embedded nut, and the safety of the external thread of the broken end and the fastening nut, the effective overlap rate of the thread between the external thread of the protection end and the embedded nut, and between the external thread of the broken end and the fastening nut is not less than 25%, and h is determined. wb The range is h wd The range is At the same time, h wb <h wd , where h ny h is the standard thread height of the internal thread of the embedded nut nj h is the standard thread height of the internal thread of the fastening nut. ny =h nj .

[0020] Furthermore, the external thread at the protection end and the external thread at the fracture end are both metric threads, the pitch of the external thread at the protection end and the fracture end is P, the thread bottom width is 0.25P, the thread angle is 60°, and the major diameter of the external thread at the protection end is d b , crest width is C wb , the major diameter of the external thread at the fracture end is d d , crest width is C wd , according to the crest width C wb He Ya Gao wb Satisfied geometric relationship Large diameter of external thread of protective end Crest width C wd He Ya Gao wd Satisfied geometric relationship Major diameter of external thread at the fracture end It can be calculated that: D - 0.812P ≤ d b <d d < D, where D is the major diameter of the internal threads of the embedded nut and the fastening nut.

[0021] Furthermore, based on the fact that the bending deflection of the rectangular cantilever beam simplified from the thread teeth of the external thread at the protection end is not greater than that of the rectangular cantilever beam simplified from the thread teeth of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam simplified from the thread teeth of the external thread at the fracture end is not greater than that of the rectangular cantilever beam simplified from the thread teeth of the internal thread of the fastening nut, it is obtained that D - 0.812P ≤ d b <d d ≤ D - 0.083P.

[0022] Furthermore, based on the fact that the bending deflection of the rectangular cantilever beam simplified from the thread teeth of the external thread at the protection end is not greater than one-tenth of that of the rectangular cantilever beam simplified from the thread teeth of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam simplified from the thread teeth of the external thread at the fracture end is not greater than one-tenth of that of the rectangular cantilever beam simplified from the thread teeth of the internal thread of the fastening nut, it is obtained that D - 0.812P ≤ d b <d d ≤ D - 0.332P.

[0023] Furthermore, both the external thread at the protection end and the external thread at the fracture end are MJ threads, the pitch of the external thread at the protection end and the external thread at the fracture end is P, and the bottom width of the thread is the thread angle is 60°, the major diameter of the external thread at the protection end is d b and the top width of the thread is C wb , the major diameter of the external thread at the fracture end is d d and the top width of the thread is C wd , according to the geometric relationship satisfied by the top width C wb and the thread height h wb The geometric relationship satisfied by The major diameter of the external thread at the protection end The top width C wd and the thread height h wd The geometric relationship satisfied by The major diameter of the external thread at the fracture end It can be calculated that: D - 0.731P ≤ d b <d d < D, where D is the major diameter of the internal threads of the embedded nut and the fastening nut.

[0024] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the protection end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the embedded nut internal thread are simplified, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the broken end are not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut are simplified, it is concluded that D-0.731P≤d b <d d ≤D-0.118P.

[0025] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the protection end are simplified is not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the embedded nut internal thread are simplified, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the broken end are not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut are simplified, it is concluded that D-0.731P≤d b <d d ≤D-0.346P.

[0026] Furthermore, the external thread of the fracture end is a standard metric thread or MJ thread, the external thread of the protection end is an improved metric thread or MJ thread, and the tooth height of the external thread of the protection end is h wb According to the safety of the cooperation between the external thread of the protection end and the embedded nut, the effective overlap rate of the thread of the external thread of the protection end and the embedded nut is guaranteed to be not less than 25%, and h is determined. wb The range is where h ny It is the standard thread height of the internal thread of the embedded nut. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of embodiment 1 of the stud bolt assembly of the present invention;

[0028] Figure 2 It is a tooth profile diagram of a standard metric thread in the prior art;

[0029] Figure 3 The tooth profile diagram of the external thread of the stud bolt in Embodiment 1 of the stud bolt assembly of the present invention;

[0030] Figure 4 It is a schematic diagram of the tooth profiles of the external thread and the internal thread in Embodiment 1 of the stud bolt assembly of the present invention being simplified into a cantilever beam;

[0031] Figure 5 k and C in the embodiment 1 of the stud bolt assembly of the present invention w The change relationship diagram of

[0032] Figure 6It is a curve diagram showing the change of the average stress at the calibrated position of bolt 1 and a comparative bolt under the same alternating load over time in Example 1 of the stud bolt assembly of the present invention;

[0033] Figure 7 It is a calibration position diagram in Embodiment 1 of the stud bolt assembly of the present invention;

[0034] Figure 8 It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 2 and the comparison bolt under the same alternating load over time in the embodiment 1 of the stud bolt assembly of the present invention;

[0035] Fig. 9 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 1 of the stud bolt assembly of the present invention;

[0036] Fig.10 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0037] Fig.11 The tooth profile diagram of the external thread of the stud bolt in Embodiment 2 of the stud bolt assembly of the present invention;

[0038] Fig.12 It is a schematic diagram of the tooth profile of the external thread and the internal thread in Embodiment 2 of the stud bolt assembly of the present invention being simplified into a cantilever beam;

[0039] Fig.13 k and C in Embodiment 2 of the stud bolt assembly of the present invention w The change relationship diagram of

[0040] Fig.14 It 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;

[0041] Fig.15 It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 5 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.16 It is a curve diagram showing the change of the average stress at the calibrated position of the bolt 6 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.17 It is a curve diagram showing the change of the average stress at the calibrated position of bolt 7, bolt 8 and bolt 9 under the same alternating load over time in Example 3 of the stud bolt assembly of the present invention;

[0044] Fig.18It is a curve diagram of the average stress variation over time at the calibrated positions of bolts 10, bolts 11 and bolts 12 in Example 4 of the stud bolt assembly of the present invention under the same alternating load. DETAILED DESCRIPTION

[0045] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0046] In response to the technical problems existing in the prior art, the basic concept of the present invention is to distinguish the external threads at both ends of the stud bolt into a protective end external thread and a broken end external thread, so that the stiffness of the external thread teeth of the protective end is greater than the stiffness of the external thread teeth of the broken end, thereby improving the fatigue performance of the external thread teeth of the protective end and making the fracture position of the stud bolt on the external thread of the broken end.

[0047] Embodiment 1 of the stud bolt assembly of the present invention:

[0048] like Figure 1 As shown, the stud bolt assembly includes a stud bolt 1 and an embedded nut 2 used in conjunction with the stud bolt 1 and embedded in a structure, and a fastening nut 3 used to be set 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 1 include a protective end external thread 11 that is connected to the embedded nut 2 and a broken end external thread 12 that is connected to the fastening nut 3. In this embodiment, the internal thread of the embedded nut 2, the internal thread of the fastening nut 3, the protective end external thread 11, and the broken end external thread 12 are all metric threads, wherein the internal thread profiles of the embedded nut 2 and the fastening nut 3 are the standard metric thread profiles, and the protective end external thread 11 and the broken end external thread 12 are evolved from the standard metric thread profiles, so the existing standard metric thread profiles are first introduced below.

[0049] 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 ).

[0050] like Figure 3 The figure shows the tooth profile of the external thread 11 at the protection end and the external thread 12 at the broken end of the stud bolt 1 in this embodiment. Figure 3The tooth profile in the thread includes the tooth top, the first straight line segment, the tooth bottom and the second straight line segment connected in sequence. The pitch of the external thread is P, the major diameter is d, the middle diameter is d2, the minor diameter is d1, the tooth profile angle α = 60°, and the tooth height is h w , the tooth bottom width is The crest width is C w There are two intersection points between the tooth top and the straight line segments on both sides, namely A and B. The line segment AB is parallel to the thread axis. The length of the line segment AB is also the tooth top width C. w .

[0051] In this embodiment, the tooth angles of the external threads at the protection end and the external threads at the fracture end are equal, both are 60°; the pitches are equal, both are P; the minor diameters are equal, both are d1. The differences are in the crest width, major diameter and tooth height, where the tooth height of the external threads at the fracture end is h wd , the major diameter is d d , crest width is C wd , the tooth height of the external thread at the protection end is h wb , the major diameter is d b , crest width is C wb , d b <d d <D、C wb >C wd , D is the major diameter of the internal threads of the embedded nut and the fastening nut. The present invention reduces the tooth height of the external threads of the protection end and the fracture end, so that the major diameters of the external threads of the protection end and the fracture end are smaller than the major diameter of the internal threads of the corresponding nut, and the rigidity of the teeth of the external threads of the protection end and the fracture end is improved to a certain extent, but the tooth height of the external threads of the protection end is reduced more, so the rigidity of the teeth of the external threads of the protection end is greater, and its fatigue performance when subjected to alternating loads is better, so that the fracture position of the stud bolt can be on the external threads of the fracture end, and then when the stud bolt breaks, it is easy to remove the stud bolt from the structure, and it is convenient for on-site replacement operations.

[0052] Theoretically, for metric threads, when the tooth height of the external thread is not reduced, the crest width should be =0.125P; when the tooth height of the external thread is reduced to zero, the crest width should be Therefore, the crest width of the external thread is C w The maximum range is: 0.125P<C w <0.75P. At the same time, when the tooth height of the external thread is not reduced, the tooth height can be obtained through geometric calculation as follows: (This value is also the tooth height h of the standard metric internal thread n , corresponding to the standard thread height h of the internal thread of the embedded nut in this embodiment ny = Standard thread height of the internal thread of the fastening nut ), so the tooth height h of the external threadw The maximum range is: From this we get

[0053]

[0054] for Figure 3 For example, the tooth height h of the external thread can be calculated based on the geometric relationship. w and tooth top width C w The following relations are satisfied: Therefore, the crest width C of the external thread at the protective end can be obtained. wb He Ya Gao wb Satisfied geometric relationship Crest width C of external thread at the fracture end wd He Ya Gao wd Satisfied geometric relationship In addition, according to the geometric relationship, we can find Figure 3 Large diameter of internal and external threads Therefore, the large diameter of the external thread of the protection end can be obtained Major diameter of external thread at the fracture end

[0055] Considering the safety of the fit between the external and internal threads, the effective overlap rate of the internal and external threads cannot be less than 25%, that is, the tooth height of the external thread must meet It can be concluded that After simplification, we can get C w ≤0.594P.

[0056] For the external thread of the protection end, according to the safety of its cooperation with the embedded nut, the effective overlap rate of the thread between the external thread of the protection end and the embedded nut is guaranteed to be not less than 25%, and h is determined. wb The range is Further we can get After simplification, we get 0.125P<C wb ≤0.594P, substitute the major diameter d of the external thread of the protection end b From the formula, we can get D-0.812P≤d b <D。

[0057] For the broken end external thread, according to the safety of its cooperation with the fastening nut, the effective overlap rate of the thread between the broken end external thread and the fastening nut is guaranteed to be no less than 25%, and h is determined. wd The range is Further we can get After simplification, we get 0.125P<C wd ≤0.594P, substitute the major diameter d of the external thread at the fracture end dIn the formula, we can obtain D - 0.812P ≤ d d <D. Since d b <d d , after integration, we get D - 0.812P ≤ d b <d d <D.

[0058] So far, the upper limit values of C wb and C wd have been optimized, that is, the lower limit value of the optimized d b . In order to further explore the upper limit value of d d for the convenience of subsequent analysis, as shown in Figure 4 , in this embodiment, the thread flanks of the external thread and the internal thread are simplified into a group of interacting rectangular cantilever beams. The acting point Q of the internal and external thread flanks is the midpoint of the overlapping area of the internal and external thread flanks. The tooth width of the simplified cantilever beam of the external thread flank is the tooth width C w1 at the equivalent acting point Q, and the tooth width of the simplified internal thread flank is also the tooth width C n1 at the equivalent acting point Q.

[0059] According to the geometric relationship, the tooth width C w1 of the external thread flank at the equivalent acting point P can be calculated as follows: The tooth width C n1 of the internal thread flank at the equivalent acting point P is:

[0060] 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.

[0061] Furthermore, the beam heights h of the simplified cantilever beams of the internal and external thread flanks are C n1 and C w1 respectively. Then the moments of inertia of the simplified cantilever beams of the internal and external thread flanks with beam width b are:

[0062] According to the knowledge of material mechanics, the deflection equation of a cantilever beam at the acting point is: where F is the load magnitude at the acting point, l is the distance from the acting point to the support position, and E is the elastic modulus of the cantilever beam.

[0063] Assume that the elastic modulus of the external thread material is E w , the lateral interaction force between the internal and external thread flanks is F, and the length from the equivalent acting point Q to the support position of the cantilever beam is Then the approximate deflection w w of the simplified cantilever beam of the external thread flank at the equivalent acting point Q is:

[0064]

[0065] 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:

[0066]

[0067] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0068]

[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]

[0071] At 0.125P<C w k plotted in the range of ≤0.594P with respect to C w The curve, such as Figure 5 As shown in the curve, it can be seen that k increases with C w The ratio of the bending deflection of the external thread to the bending deflection of the internal thread decreases with the increase of the tooth width C of the external thread. w As the value of P increases, it gradually decreases. w In the range of ≤0.594P, the use of external threads in combination with standard metric internal threads can reduce the bending deflection of the external thread teeth, which is equivalent to increasing the bending deflection of the internal thread teeth, so that the internal thread 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 under the action of the alternating load, and improving the fatigue performance of the external thread.

[0072] Furthermore, when k = 1, the bending deflection of the external thread is equal to the bending deflection of the internal thread, We can find C w =0.173P. Therefore, when k < 1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread teeth begins to be smaller than the bending deflection of the internal thread teeth, that is: C w >0.173P. w ≥0.173P substitution It can be obtained that d≤D-0.083P.

[0073] Furthermore, for the major diameter d of the external thread at the fracture end d and the major diameter d of the external thread of the protection end b For example, we can conclude that D-0.812P≤d b <d d ≤D-0.083P, within this range, the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the protection end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the embedded nut internal thread are simplified, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the broken end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the fastening nut internal thread are simplified. Therefore, it can ensure that the effective overlap rate of the thread teeth of the internal and external threads is not less than 25% of the height of the internal thread teeth, ensuring the safety of the matching of the internal and external threads, and at the same time, it can also ensure that the bending deflection of the external thread teeth is not greater than the bending deflection of the internal thread teeth, and the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load.

[0074] Furthermore, when k≤0.1, C w ≥0.317P. Substitute It can be obtained that d≤D-0.332P. Further, for the major diameter d of the external thread at the fracture end d and the major diameter d of the external thread of the protection end b For example, we can conclude that D-0.812P≤d b <d d ≤D-0.332P. Within this range, the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the protection end are simplified is not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the broken end are not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut. The internal thread can be further bent and deformed to absorb the inertia force generated by the alternating load, thereby further improving the fatigue performance of the external thread.

[0075] In order to verify the major diameter d of the external thread at the fracture end provided in this embodiment d and the major diameter d of the external thread of the protection end b In order to show the superiority of the range, a comparative test was carried out.

[0076] As shown in Table 1, the detailed parameters of three kinds of stud bolts are given in this test. The internal threads of the embedded nuts and fastening nuts used in conjunction with the three kinds of stud bolts are all standard metric internal threads. The pitch of the internal threads and the pitch of the external threads at both ends of the stud bolts are both 4 mm. In addition, the external threads at both ends of the comparison bolt are also standard metric threads, and the corresponding embedded nuts and fastening nuts are both standard metric nuts with a pitch of 4 mm. Among them, the major diameter D of the internal threads of the embedded nuts and fastening nuts is 36 mm. It can be calculated that D - 0.812P = 32.752 mm, D - 0.083P = 35.668 mm, and D - 0.332P = 34.672 mm.

[0077] Table 1 Key Parameters of Stud Bolts

[0078]

[0079] Among them, the major diameter d of the external thread at the fracture end of Bolt 1 d = 35.826 mm, within the range of D - 0.083P < d d < D; the major diameter d of the external thread at the protection end b = 35.134 mm, within the range of D - 0.332P < d b < D - 0.083P. According to the above set parameters, the internal and external threads are subjected to dynamic analysis 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. Under the same alternating load, the average stress-time curves of Bolt 1, Bolt 2, Bolt 3, and the comparison bolt at the calibration positions (the bolt has calibration positions at both the fracture end and the protection end, and the calibration position is the red dot position in Figure 7 , that is, the first thread position where the external thread of the bolt mates with the nut, which is usually also the position where the stress is most concentrated. The calibration positions of the following test bolts are the same as this) are obtained. Figure 6 The average stress-time curves of Bolt 1 and the comparison bolt at the calibration positions under the same alternating load are shown. From Figure 6 it can be seen that the average stresses at the fracture end and the protection end of Bolt 1 are less than those of the comparison bolt. This shows that Bolt 1 has better fatigue resistance. And because the average stress at the protection end of Bolt 1 is less than that at the fracture end, when fatigue fracture occurs, the bolt fractures preferentially at the fracture end.

[0080] The major diameter d of the external thread at the fracture end of Bolt 2 d = 35.134 mm, within the range of D - 0.332P < d d < D - 0.083P; the major diameter d of the external thread at the protection end b = 33.6 mm, within the range of D - 0.812P < d b < D - 0.332P. Figure 8 The figure shows the curves of the mean stress at the calibrated positions of bolt 2 and the comparison bolt varying with time under the action of the same alternating load. It can be seen from the figure that the mean stresses at the fracture end and the protection end of bolt 2 are less than those of the comparison bolt, indicating that bolt 2 has better fatigue resistance. Moreover, since the mean stress at the protection end of bolt 2 is less than that at the fracture end, when fatigue fracture occurs, the bolt preferentially fractures at the fracture end.

[0081] The major diameter d of the external thread at the fracture end of bolt 3 d = 33.6 mm, within the range of D - 0.812P < d b < D - 0.332P; the major diameter d of the external thread at the protection end b = 33.05, within the range of D - 0.812P < d b < D - 0.332P. Fig. 9 The figure shows the curves of the mean stress at the calibrated positions of bolt 3 and the comparison bolt varying with time under the action of the same alternating load. It can be seen from the figure that the mean stresses at the fracture end and the protection end of bolt 3 are less than those of the comparison bolt, indicating that bolt 3 has better fatigue resistance. Moreover, since the mean stress at the protection end of bolt 3 is less than that at the fracture end, when fatigue fracture occurs, the bolt preferentially fractures at the fracture end.

[0082] From Figure 6 , Figure 8 and Fig. 9 it can be seen that when the major diameter of the external thread of the stud bolt is less than D - 0.332P, the mean stress of the thread is significantly reduced, and the fatigue performance of the bolt is significantly improved.

[0083] Embodiment 2 of the stud bolt assembly in the present invention:

[0084] In this embodiment, the external threads at the protection end and the fracture end of the stud bolt are both MJ threads, and the internal threads of the embedded nut and the fastening nut that cooperate with them are standard MJ threads. The tooth profiles of the external threads at the protection end and the fracture end are both evolved from the tooth profile of the standard MJ thread. Therefore, the tooth profile of the existing standard MJ thread will be introduced first. As Fig.10 shown, D in the figure is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the pitch diameter of the internal thread, d2 is the pitch 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 width of the tooth top of the internal thread is The width of the tooth bottom is The width of the tooth top of the external thread is The width of the tooth bottom is Since the thread angles of the internal and external threads are both 60°, the thread heights of the internal and external threads can be obtained through geometric calculation as (that is, Fig.10 in ).

[0085] Fig.11 The figure shows the tooth profile of the external thread at the protection end and the external thread at the broken end of the stud bolt in this embodiment. It can be seen from the figure that the tooth profile includes the tooth top, the first straight line segment, the tooth bottom and the second straight line segment connected in sequence. The pitch of the external thread is P, the major diameter is d, the middle diameter is d2, the minor diameter is d1, the tooth profile angle α=60°, and the tooth height is h w , the tooth bottom width is The crest width is C w There are two intersection points between the tooth top and the straight line segments on both sides, namely A and B. The line segment AB is parallel to the thread axis. The length of the line segment AB is also the tooth top width C. w .

[0086] In this embodiment, the tooth angles of the external threads at the protection end and the external threads at the fracture end are equal, both are 60°; the pitches are equal, both are P; the minor diameters are equal, both are d1. The differences are in the crest width, major diameter and tooth height, where the tooth height of the external threads at the fracture end is h wd , the major diameter is d d , crest width is C wd , the tooth height of the external thread at the protection end is h wb , the major diameter is d b , crest width is C wb , d b <d d <D、C wb >C wd , D is the major diameter of the internal thread of the embedded nut and the fastening nut. By reducing the tooth height of the external thread at the protection end and the external thread at the fracture end, the major diameter of the external thread at the protection end and the external thread at the fracture end are smaller than the major diameter of the internal thread of the corresponding nut, which improves the stiffness of the external thread at the protection end and the external thread at the fracture end to a certain extent. However, the tooth height of the external thread at the protection end is reduced more, so the stiffness of the external thread at the protection end is greater, and its fatigue performance when subjected to alternating loads is better, so that the fracture position of the stud bolt can be on the external thread at the fracture end, and then when the stud bolt breaks, it is easy to remove the stud bolt from the structure, which is convenient for on-site replacement operations.

[0087] Theoretically, for MJ threads, when the external thread height is not reduced, the crest width should be When the tooth height of the external thread is reduced to zero, the crest width should be Therefore, the crest width of the external thread is C w The maximum range is: At the same time, when the tooth height of the external thread is not reduced, the tooth height can be obtained through geometric calculation: (This value is also the standard MJ internal thread height h n, corresponding to the standard thread height h of the internal thread of the embedded nut in this embodiment ny = Standard thread height of the internal thread of the fastening nut ), so the tooth height h of the external thread w The maximum range is: From this we get

[0088] for Fig.11 For example, the tooth height h of the external thread can be calculated based on the geometric relationship. w and tooth top width C w The following relations are satisfied: Therefore, the crest width C of the external thread at the protective end can be obtained. wb He Ya Gao wb Satisfied geometric relationship Crest width C of external thread at the fracture end wd He Ya Gao wd Satisfied geometric relationship In addition, according to the geometric relationship, we can find Fig.11 Large diameter of internal and external threads Therefore, the large diameter of the external thread of the protection end can be obtained Major diameter of external thread at the fracture end

[0089] Considering the safety of the fit between the external and internal threads, the effective overlap rate of the internal and external threads cannot be less than 25%, that is, the tooth height of the MJ external thread must meet It can be concluded that After simplification, we can get C w ≤0.547P.

[0090] For the external thread of the protection end, according to the safety of its cooperation with the embedded nut, the effective overlap rate of the thread between the external thread of the protection end and the embedded nut is guaranteed to be not less than 25%, and h is determined. wb The range is Further we can get After simplification, we get 0.125P<C wb ≤0.547P, substitute the major diameter d of the external thread of the protection end b From the formula, we can get D-0.731P≤d b <D。

[0091] For the broken end external thread, according to the safety of its cooperation with the fastening nut, the effective overlap rate of the thread between the broken end external thread and the fastening nut is guaranteed to be no less than 25%, and h is determined. wd The range is Further information is available After simplification, we get 0.125P<C wd≤0.547P, substitute it into the major diameter d of the external thread at the fracture end d in the formula, we can get D - 0.731P ≤ d d < D. Since d b < d d , so after integration, we get D - 0.731P ≤ d b < d d < D.

[0092] So far, the upper limit values of C wb and C wd are optimized, that is, the lower limit value of d b is optimized. In order to further explore the upper limit value of d d for the convenience of subsequent analysis, as Fig.12 shown, in this embodiment, the thread flanks of the external thread and the internal thread are simplified into a group of interacting rectangular cantilever beams. The acting point Q of the internal and external thread flanks is the midpoint of the overlapping area of the internal and external thread flanks. The tooth width of the simplified cantilever beam of the external thread flank is the tooth width C w1 at the equivalent acting point Q, and the tooth width of the simplified internal thread flank is also the tooth width C n1 at the equivalent acting point Q.

[0093] According to the geometric relationship, the tooth width C w1 of the external thread flank at the equivalent acting point P can be calculated as follows: The tooth width C n1 of the internal thread flank at the equivalent acting point P is:

[0094] 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.

[0095] Furthermore, the beam heights h of the simplified cantilever beams of the internal and external thread flanks are C n1 and C w1 respectively. Then the moments of inertia of the simplified cantilever beams of the internal and external thread flanks with beam width b are:

[0096] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the acting point is: where F is the load magnitude at the acting point, l is the distance from the acting point to the support position, and E is the elastic modulus of the cantilever beam.

[0097] Assume that the elastic modulus of the material of the MJ external thread is E w , the lateral interaction force between the internal and external thread flanks is F, and the length from the equivalent acting point Q to the support position of the cantilever beam is Then the approximate deflection w generated by the simplified cantilever beam of the MJ external thread flank at the equivalent acting point Qw for:

[0098]

[0099] Assume that the material elastic modulus of the MJ internal thread 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:

[0100]

[0101] Furthermore, the ratio of the MJ external thread deflection to the MJ internal thread deflection is defined as k, then k is:

[0102]

[0103] 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:

[0104]

[0105] At 0.125P<C w Plot k about C in the range of ≤0.547P w The curve, such as Fig.13 As shown in the curve, it can be seen that k increases with C w The ratio of the bending deflection of the external thread to the bending deflection of the internal thread decreases with the increase of the tooth width C of the external thread. w As the value of P increases, it gradually decreases. w In the range of ≤0.547P, the MJ external thread of this embodiment can be used in combination with the standard MJ internal thread to reduce the bending deflection of the MJ external thread teeth, which is equivalent to increasing the bending deflection of the internal thread teeth, so that the internal thread 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 under the action of the alternating load, and improving the fatigue performance of the external thread.

[0106] Furthermore, when k≤1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread teeth is not greater than the bending deflection of the internal thread teeth, that is: C w ≥0.193P. w ≥0.193P substitution It can be obtained that d≤D-0.118P.

[0107] Furthermore, for the major diameter d of the external thread at the fracture end d and the major diameter d of the external thread of the protection end b For example, we can conclude that D-0.731P≤d b <d d ≤D-0.118P, within this range, the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the protection end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the embedded nut are simplified, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the broken end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut are simplified. Therefore, it can ensure that the effective overlap rate of the thread teeth of the internal and external threads is not less than 25% of the height of the internal thread teeth, ensure the safety of the matching of the internal and external threads, and at the same time, it can also ensure that the bending deflection of the external thread teeth is not greater than the bending deflection of the internal thread teeth, and the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load.

[0108] Furthermore, when k≤0.1, C w ≥0.325P. w ≥0.325P Substitute It can be obtained that d≤D-0.346P. Further, for the major diameter d of the external thread at the fracture end d and the major diameter d of the external thread of the protection end b For example, we can conclude that D-0.731P≤d b <d d ≤D-0.346P. Within this range, the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the protection end are simplified is not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the embedded nut, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread at the broken end are not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut. The internal thread can be further bent and deformed to absorb the inertia force generated by the alternating load, thereby further improving the fatigue performance of the external thread.

[0109] In order to verify the major diameter d of the external thread at the fracture end provided in this embodiment d and the major diameter d of the external thread of the protection end b In order to show the superiority of the range, a comparative test was carried out.

[0110] As shown in Table 2, the present test gives the detailed parameters of three kinds of double-headed bolts. The internal threads of the embedded nuts and fastening nuts used in conjunction with the three kinds of double-headed bolts are all standard MJ internal threads. The pitch of the internal thread and the pitch of the external threads at both ends of the double-headed bolt are both 4 mm. In addition, the external threads at both ends of the comparison bolt are also standard MJ threads, and the corresponding embedded nuts and fastening nuts are both standard MJ nuts, and the pitch is also 4 mm. Among them, the major diameter D of the internal threads of the embedded nut and the fastening nut is 36 mm. It can be calculated that D - 0.731P = 33.076 mm, D - 0.118P = 35.528 mm, and D - 0.346P = 34.616 mm.

[0111] Table 2 Key Parameters of Double-Headed Bolts

[0112]

[0113] Among them, the major diameter d of the external thread at the fracture end of bolt 4 d = 35.824 mm, within the range of D - 0.118P < d d < D; the major diameter d of the external thread at the protection end b = 35.132 mm, within the range of D - 0.346P < d d < D - 0.118P. According to the above set parameters, the internal and external threads are analyzed dynamically 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. The curves of the average stress at the calibration position of bolt 4, bolt 5, bolt 6, and the comparison bolt changing with time under the same alternating load are obtained.

[0114] Fig.14 The curves of the average stress at the calibration position of bolt 4 and the comparison bolt changing with time under the same alternating load are shown. It can be seen from the figure that the average stresses at the fracture end and the protection end of bolt 4 are less than those of the comparison bolt. This shows that the fatigue resistance of bolt 4 is better. And because the average stress at the protection end of bolt 4 is less than that at the fracture end, when fatigue fracture occurs, the bolt preferentially fractures at the fracture end.

[0115] The major diameter d of the external thread at the fracture end of bolt 5 d = 35.132 mm, within the range of D - 0.346P < d d < D - 0.118P; the major diameter d of the external thread at the protection end b = 34.092 mm, within the range of D - 0.731P < d d < D - 0.346P. Fig.15The figure shows the curves of the mean stress at the calibrated positions of bolt 5 and the comparison bolt varying with time under the action of the same alternating load. It can be seen from the figure that the mean stresses at the fracture end and the protection end of bolt 5 are less than those of the comparison bolt. This shows that bolt 5 has better anti-fatigue performance. And because the mean stress at the protection end of bolt 5 is less than that at the fracture end, when fatigue fracture occurs, the bolt preferentially fractures at the fracture end.

[0116] The major diameter d of the external thread at the fracture end of bolt 6 d = 34.092 mm, within the range of D - 0.731P < d d < D - 0.346P; the major diameter d of the external thread at the protection end b = 33.746 mm, within the range of D - 0.731P < d d < D - 0.346P. Fig.16 The figure shows the curves of the mean stress at the calibrated positions of bolt 6 and the comparison bolt varying with time under the action of the same alternating load. It can be seen from the figure that the mean stresses at the fracture end and the protection end of bolt 6 are less than those of the comparison bolt. This shows that bolt 6 has better anti-fatigue performance. And because the mean stress at the protection end of bolt 6 is less than that at the fracture end, when fatigue fracture occurs, the bolt preferentially fractures at the fracture end.

[0117] From Figure 14-16 it can be seen that when the major diameter of the external thread of the stud bolt is less than D - 0.346P, the mean stress of the thread decreases significantly, and the fatigue performance of the bolt is significantly improved.

[0118] Example 3 of the stud bolt assembly in the present invention:

[0119] In this example, the external threads at the protection end and the fracture end of the stud bolt are both metric threads, and the internal threads of the embedded nut and the fastening nut used in cooperation are both standard metric threads. Different from Example 1, the external thread at the fracture end in this example is a standard metric thread, that is, the tooth height and the major diameter of the external thread at the fracture end are the same as those of the standard metric external thread, and it is a standard thread profile. The tooth height and the major diameter of the external thread at the fracture end are not reduced, and only the tooth height and the major diameter of the external thread at the protection end are reduced. The specific situation is the same as that in Example 1. According to the safety of the cooperation between the external thread at the protection end and the embedded nut, to ensure that the effective coincidence rate of the thread teeth between the external thread at the protection end and the embedded nut is not less than 25%, the range of the tooth height h wb is where h ny is the standard tooth height of the internal thread of the embedded nut. Through the same process, it can be determined that D - 0.812P ≤ d b<D, P is the pitch of the external thread of the protection end, and D is the major diameter of the internal thread of the embedded nut. Then, according to the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread of the protection end is not greater than the bending deflection of the rectangular cantilever beam simplified from the thread of the internal thread of the embedded nut, it is further determined that D - 0.812P ≤ d b ≤ D - 0.083P. Finally, according to the bending deflection of the rectangular cantilever beam simplified from the thread of the external thread of the protection end is not greater than one-tenth of the bending deflection of the rectangular cantilever beam simplified from the thread of the internal thread of the embedded nut, the final range D - 0.812P ≤ d b ≤ D - 0.332P.

[0120] This embodiment also provides a comparative test. As shown in Table 3, this test gives the detailed parameters of three double-headed bolts. The internal threads of the embedded nuts and fastening nuts used in conjunction with the three double-headed bolts are all standard metric internal threads. The pitch of the internal thread and the pitch of the external threads at both ends of the double-headed bolts are both 4 mm. The other key parameters are shown in Table 1. The parameters of the external threads at the fracture ends of the three double-headed bolts are the same, and the parameters of the external threads at the protection ends are different.

[0121] Table 3 Key Parameters of Double-Head Bolts

[0122]

[0123]

[0124] According to the above set parameters, the dynamics analysis of the internal and external threads is carried out 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. The curves of the average stress at the calibration position of bolts 7, 8, 9 and the comparison bolt changing with time under the same alternating load are obtained.

[0125] Fig.17 The curves of the average stress at the calibration position of bolts 7 - 9 changing with time under the same alternating load are shown. It can be seen from the figure that the average stresses of the external threads at the fracture ends of the three double-headed bolts are equal and greater than the average stress of the external thread at the protection end.

[0126] Table 4 shows the stress amplitudes (maximum stress minus minimum stress) of the external threads of the three bolts and the amplitude differences between the fracture end and the protection end. It can be seen from this that the stress amplitudes of the fracture ends of the three double-headed bolts are greater than the stress amplitudes of the protection ends, that is, the fatigue performance of the protection ends of the double-headed bolts is better than that of the protection ends. When fatigue fracture occurs, the bolt fractures preferentially at the fracture end.

[0127] Table 4 Stress Amplitudes and Amplitude Differences of Double-Head Bolts

[0128] Bolt 7 Bolt 8 Bolt 9 Broken end 147.335Mpa 147.335Mpa 147.335Mpa Protection end 146.926Mpa 145.402Mpa 140.856Mpa Amplitude difference 0.409Mpa 1.933Mpa 6.472Mpa

[0129] Embodiment 4 of the double-headed bolt assembly in the present invention:

[0130] In this embodiment, the external threads of the protected end and the fractured end of the double-headed bolt are both MJ threads, and the internal threads of the embedded nut and the fastening nut used in cooperation are both standard MJ threads. Different from Embodiment 2, the external thread of the fractured end in this embodiment is a standard MJ thread, that is, the tooth height and major diameter of the external thread of the fractured end are the same as those of the standard MJ external thread, and it is a standard thread profile. The tooth height and major diameter of the external thread of the fractured end are not reduced, but only the tooth height and major diameter of the external thread of the protected end are reduced. The specific situation is the same as that in Embodiment 2. According to the safety of the cooperation between the external thread of the protected end and the embedded nut, to ensure that the effective coincidence rate of the thread teeth between the external thread of the protected end and the embedded nut is not less than 25%, the tooth height h wb The range of is where h ny is the standard tooth height of the internal thread of the embedded nut. Through the same process, it can be determined that D - 0.731P ≤ d b < D, where P is the pitch of the external thread of the protected end, and D is the major diameter of the internal thread of the embedded nut. Then, according to the bending deflection of the simplified rectangular cantilever beam of the thread teeth of the external thread of the protected end not being greater than the bending deflection of the simplified rectangular cantilever beam of the thread teeth of the internal thread of the embedded nut, it is further determined that D - 0.731P ≤ d b ≤ D - 0.118P. Finally, according to the bending deflection of the simplified rectangular cantilever beam of the thread teeth of the external thread of the protected end not being greater than one-tenth of the bending deflection of the simplified rectangular cantilever beam of the thread teeth of the internal thread of the embedded nut, the final range D - 0.731P ≤ d b ≤ D - 0.346P is determined.

[0131] This embodiment also provides a comparative test. As shown in Table 5, this test gives the detailed parameters of three double-headed bolts. The internal threads of the embedded nuts and the fastening nuts used in cooperation with the three double-headed bolts are all standard MJ internal threads. The pitch of the internal threads and the pitches of the external threads at both ends of the double-headed bolts are all 4 mm. The other key parameters are shown in Table 5. The parameters of the external threads of the fractured ends of the three double-headed bolts are the same, and the parameters of the external threads of the protected ends are different.

[0132] Table 5 Key parameters of the double-headed bolt

[0133]

[0134] According to the above set 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 applied to the nut, and an alternating load that changes with time is applied to the bolt. The average stress-time curves at the calibration positions of Bolt 10, Bolt 11, Bolt 12, and the comparison bolt under the same alternating load are obtained.

[0135] Fig.18 Shown is the curve of the mean stress at the calibrated position of bolt 10-12 varying with time under the same alternating load. It can be seen from the figure that the mean stresses of the external threads at the fracture ends of the three stud bolts are equal and greater than the mean stress of the external thread at the protection end.

[0136] Table 6 shows the stress amplitudes (maximum stress minus minimum stress) of the external threads of the three bolts and the amplitude differences between the fracture ends and the protection ends. From this, it can be known that the stress amplitudes of the fracture ends of the three stud bolts are greater than the stress amplitudes of the protection ends, that is, the fatigue performance of the protection ends of the stud bolts is better than that of the protection ends. When fatigue fracture occurs, the bolt fractures preferentially at the fracture end.

[0137] Table 6 Stress amplitudes and amplitude differences of stud bolts

[0138] Bolt 10 Bolt 11 Bolt 12 Broken end 147.335Mpa 147.335Mpa 147.335Mpa Protection end 146.926Mpa 145.402Mpa 140.856Mpa Amplitude difference 0.409Mpa 1.933Mpa 6.472Mpa

[0139] In other embodiments of the stud bolt assembly: Different from Embodiment 2, in the process of determining the upper limit value of d d ≤ D - 0.346P, k can also take other values, such as k = 0.15, 0.2, 0.25 or other values less than 1, which can ensure that the bending deflection of the simplified rectangular cantilever beam of the external thread tooth is not greater than that of the simplified rectangular cantilever beam of the internal thread tooth of the embedded nut. Of course, k can also take values greater than 1, as long as D - 0.731P ≤ d d < d b < d d < D, it can ensure that the bolt fractures preferentially at the fracture end.

[0140] In other embodiments of the stud bolt assembly: Different from Embodiment 1, in the process of determining the upper limit value of d d ≤ D - 0.332P, k can also take other values, such as k = 0.15, 0.2, 0.25 or other values less than 1, which can ensure that the bending deflection of the simplified rectangular cantilever beam of the external thread tooth is not greater than that of the simplified rectangular cantilever beam of the internal thread tooth of the embedded nut. Of course, k can also take values greater than 1, as long as D - 0.812P ≤ d d < d b < d d < D, it can ensure that the bolt fractures preferentially at the fracture end.

[0141] In the embodiments of the stud bolt of the present invention: The specific structure of the stud bolt is the same as that of the stud bolt in any of the above-mentioned stud bolt assembly embodiments, and will not be repeated here.

[0142] 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 stud bolt, characterized in that: The external threads at both ends of the stud bolt include a protective end external thread for cooperating with an embedded nut inside the structure and a broken end external thread for cooperating with a fastening nut outside the structure. Both the protective end external thread and the broken end external thread are metric threads or MJ threads, and the tooth angle, pitch and minor diameter of the external threads are respectively equal, and the major diameter of the protective end external thread is smaller than the major diameter of the broken end external thread.

2. The stud bolt according to claim 1, characterized in that: Define the thread height of the external thread at the fracture end as h wd , the tooth height of the external thread at the protection end is h wb According to the safety of the external thread of the protection end and the embedded nut, and the safety of the external thread of the broken end and the fastening nut, the effective overlap rate of the thread between the external thread of the protection end and the embedded nut, and between the external thread of the broken end and the fastening nut is not less than 25%, and h is determined. wb The range is h wd The range is At the same time, h wb <h wd , where h ny h is the standard thread height of the internal thread of the embedded nut nj h is the standard thread height of the internal thread of the fastening nut. ny =h nj .

3. The stud bolt according to claim 2, characterized in that: The external threads of the protection end and the fracture end are both metric threads. The pitch of the external threads of the protection end and the fracture end is P, the bottom width of the tooth is 0.25P, and the tooth profile angle is 60°. The major diameter of the external thread of the protection end is d b and the top width of the tooth is C wb , the major diameter of the external thread of the fracture end is d d and the top width of the tooth is C wd . According to the geometric relationship satisfied by the top width C wb and the tooth height h wb The geometric relationship satisfied by the major diameter of the external thread of the protection end the top width C wd and the tooth height h wd is satisfied The major diameter of the external thread of the fracture end can be calculated as: D - 0.812P ≤ d b < d d < D, where D is the major diameter of the internal threads of the embedded nut and the fastening nut 4. The stud bolt according to claim 3, characterized in that: According to the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the protection end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the embedded nut internal thread are simplified, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the broken end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut are simplified, it is concluded that D-0.812P≤d b <d d ≤D-0.083P.

5. The stud bolt according to claim 4, characterized in that: According to the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the external thread of the protection end is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the embedded nut internal thread, and the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the external thread of the broken end is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread of the fastening nut, it is concluded that D-0.812P≤d b <d d ≤D-0.332P.

6. The stud bolt according to claim 2, characterized in that: Both the external thread of the protection end and the external thread of the fracture end are MJ threads. The pitch of the external thread of the protection end and the external thread of the fracture end is P, and the bottom width of the tooth is The thread angle is 60°. The major diameter of the external thread of the protection end is d b and the top width of the tooth is C wb The major diameter of the external thread of the fracture end is d d and the top width of the tooth is C wd According to the geometric relationship satisfied by the top width C wb and the tooth height h wb The geometric relationship satisfied by the major diameter of the external thread of the protection end the top width C wd and the tooth height h wd The geometric relationship satisfied by the major diameter of the external thread of the fracture end can be calculated as: D - 0.731P ≤ d b < d d < D, where D is the major diameter of the internal threads of the embedded nut and the fastening nut.

7. The stud bolt according to claim 6, characterized in that: According to the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the protection end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the embedded nut internal thread are simplified, and the bending deflection of the rectangular cantilever beam after the thread teeth of the external thread of the broken end are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread of the fastening nut are simplified, it is concluded that D-0.731P≤d b <d d ≤D-0.118P。 8. The stud bolt according to claim 7, characterized in that: According to the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the external thread of the protection end is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the embedded nut internal thread, and the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the external thread of the broken end is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread of the fastening nut, it is concluded that D-0.731P≤d b <d d ≤D-0.346P.

9. The stud bolt according to claim 1, characterized in that: The external thread of the broken end is a standard metric thread or MJ thread, the external thread of the protection end is an improved metric thread or MJ thread, and the tooth height of the external thread of the protection end is h wb According to the safety of the cooperation between the external thread of the protection end and the embedded nut, the effective overlap rate of the thread of the external thread of the protection end and the embedded nut is guaranteed to be not less than 25%, and h is determined. wb The range is where h ny It is the standard thread height of the internal thread of the embedded nut.

10. A stud bolt assembly, comprising a stud bolt, an embedded nut used in conjunction with the stud bolt and embedded in a structure, and a fastening nut used to be arranged outside the structure, characterized in that: The stud bolt is the stud bolt according to any one of claims 1 to 9.

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