Method and system for determining shear fatigue life curve of sandwich structure under random excitation

Abstract

The invention provides a method and system for determining a shear fatigue life curve of a sandwich structure under random excitation, and the method comprises the steps: carrying out a fatigue life test under a certain random vibration load, and obtaining a random fatigue life; establishing a dynamic response numerical analysis model consistent with the sandwich structure test piece, and solving shear root mean square stress; calculating peak value interlayer shear stress under narrow-band excitation; establishing a two-parameter interlayer shear fatigue life model under the equal-amplitude fatigue condition that R is equal to-1; substituting the random fatigue life t0, the peak inter-layer shear stress # imgabs0 # under narrow-band excitation and the inter-layer shear static strength tault into a two-parameter inter-layer shear fatigue life model, and calculating to obtain a fitting constant beta related to the material; and substituting the fitting constant beta related to the material into the two-parameter interlayer shear fatigue life model, and drawing a curve to obtain a shear root mean square stress and fatigue life curve under the random load. By applying the technical scheme provided by the invention, the technical problem of high test cost for determining the fatigue life curve in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of random vibration fatigue life prediction, and in particular to a method and system for determining a shear fatigue life curve under random excitation of a sandwich structure. Background Art

[0002] In the field of aerospace, aircraft structures are always in a vibration environment during use. Structural fatigue damage caused by vibration is one of the main modes of aircraft structure damage and a common problem in the development and use of aviation weapons and equipment. Especially for sandwich structures with lightweight design, shear delamination damage of the core layer under vibration load is one of the main failure modes of fatigue damage. Therefore, the shear fatigue life assessment of sandwich structures under random basic excitation is a very important topic.

[0003] Engineering units can obtain vibration fatigue life curves for typical structural characteristics by conducting a large number of experimental studies. By designing several structural base components, conducting random vibration tests under multiple load levels, measuring the median fatigue life under different stress levels, and then fitting the fatigue life curve of such structures. This method often requires a lot of experimental costs. Summary of the invention

[0004] The present invention provides a method and system for determining a shear fatigue life curve under random excitation of a sandwich structure, which can solve the technical problem of high cost of fatigue life curve determination test in the prior art.

[0005] According to one aspect of the present invention, a method for determining a shear fatigue life curve under random excitation of a sandwich structure is provided, and the method for determining a shear fatigue life curve under random excitation of a sandwich structure comprises: step one, carrying out a fatigue life test under a certain random vibration load on a sandwich structure test piece, and obtaining the moment when a shear crack appears under the load, that is, the random fatigue life t0 under the load; step two, establishing a dynamic response numerical analysis model consistent with the sandwich structure test piece in finite element software, keeping the boundary conditions and load levels consistent with the test, and solving to obtain the interlaminar shear root mean square stress of the sandwich structure under the random load. Step 3: According to the shear root mean square stress between the sandwich structures Calculate the peak interlaminar shear stress under narrowband excitation Step 4: Establish a dual-parameter interlaminar shear fatigue life model under R = -1 equal amplitude fatigue condition; Step 5: Convert the peak interlaminar shear stress under narrow band excitation to The peak stress level τ of interlaminar shear static fatigue test 13 Correspondingly, the random fatigue life t0 and the peak interlaminar shear stress under narrowband excitation are And interlaminar shear static strength τ ultSubstitute it into the dual-parameter interlaminar shear fatigue life model to calculate and obtain the fitting constant β related to the material; Step six, substitute the fitting constant β related to the material into the dual-parameter interlaminar shear fatigue life model and draw a curve to obtain the shear root mean square stress and fatigue life curve under random load.

[0006] Furthermore, in step 2, the boundary condition refers to the fixing of the connection holes on both sides of the test piece fixture, and the loading condition refers to the random vibration load spectrum used in the loading test.

[0007] Furthermore, in step 3, the peak interlaminar shear stress under narrowband excitation is According to Wherein, α is the ratio of the peak interlaminar shear stress under narrow-band excitation to the interlaminar shear root mean square stress of the sandwich structure, and the value of α is 2.5 to 3.5.

[0008] Furthermore, the two-parameter interlaminar shear fatigue life model is τ 13 =τ ult t -1 / β , where τ 13 is the peak stress level of interlaminar shear static fatigue test, t is the fatigue life, τ ult is the interlaminar shear static strength of the sandwich material, and β is a fitting constant related to the material.

[0009] Furthermore, the shear RMS stress and fatigue life curve under random load is given by Calculate acquisition.

[0010] Furthermore, the ratio α of the peak interlaminar shear stress under narrowband excitation to the interlaminar shear root mean square stress of the sandwich structure is 3.5.

[0011] According to another aspect of the present invention, a system for determining a shear fatigue life curve under random excitation of a sandwich structure is provided. The system for determining a shear fatigue life curve under random excitation of a sandwich structure uses the method for determining a shear fatigue life curve under random excitation of a sandwich structure as described above to determine a shear fatigue life curve.

[0012] By applying the technical solution of the present invention, a method for determining the shear fatigue life curve of a sandwich structure under random excitation is provided. The method is based on the proportional relationship between the peak stress and the root mean square stress of the response under narrowband excitation, and the narrowband random stress is equivalent to a constant amplitude stress load. In combination with failure modes and numerical calculations, a random fatigue life curve can be established by only conducting random fatigue tests under a single stress level. The fatigue life curve can be used to predict the crack initiation life when a sandwich structure fails in rapid shear fatigue under random basic excitation loads of different magnitudes. Compared with existing solutions, the present invention combines failure modes and numerical calculations, and can establish a random fatigue life curve of a sandwich structure by only conducting random fatigue tests under a single stress level, which can then be used to predict the shear fatigue life under different vibration levels. It has the advantages of requiring fewer test data points, reducing test costs, and improving calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 A flow chart showing a method for determining a shear fatigue life curve under random excitation of a sandwich structure provided according to a specific embodiment of the present invention is shown;

[0015] Figure 2 A schematic diagram of a dynamic response numerical analysis model provided according to a specific embodiment of the present invention is shown;

[0016] Figure 3 The figure shows a random fatigue life curve established according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0017] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0019] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0020] like Figures 1 to 3 As shown, according to a specific embodiment of the present invention, a method for determining a shear fatigue life curve under random excitation of a sandwich structure is provided, and the method for determining a shear fatigue life curve under random excitation of a sandwich structure comprises: step one, carrying out a fatigue life test under a certain random vibration load on a sandwich structure test piece, and obtaining the moment when a shear crack appears under the load, that is, the random fatigue life t0 under the load; step two, establishing a dynamic response numerical analysis model consistent with the sandwich structure test piece in finite element software, keeping the boundary conditions and load levels consistent with the experiment, and solving to obtain the interlayer shear root mean square stress of the sandwich structure under the random load. Step 3: According to the shear root mean square stress between the sandwich structures Calculate the peak interlaminar shear stress under narrowband excitation Step 4: Establish a dual-parameter interlaminar shear fatigue life model under R = -1 equal amplitude fatigue condition; Step 5: Convert the peak interlaminar shear stress under narrow band excitation to The peak stress level τ of interlaminar shear static fatigue test 13 Correspondingly, the random fatigue life t0 and the peak interlaminar shear stress under narrowband excitation are And interlaminar shear static strength τ ultSubstitute it into the dual-parameter interlaminar shear fatigue life model to calculate and obtain the fitting constant β related to the material; Step six, substitute the fitting constant β related to the material into the dual-parameter interlaminar shear fatigue life model and draw a curve to obtain the shear root mean square stress and fatigue life curve under random load.

[0021] By applying this configuration, a method for determining the shear fatigue life curve of a sandwich structure under random excitation is provided. This method is based on the proportional relationship between the peak stress and the root mean square stress of the response under narrowband excitation, and the narrowband random stress is equivalent to a constant amplitude stress load. In combination with failure modes and numerical calculations, a random fatigue life curve can be established by only conducting random fatigue tests under a single stress level. This fatigue life curve can be used to predict the crack initiation life when a sandwich structure fails in rapid shear fatigue under random basic excitation loads of different magnitudes. Compared with existing solutions, the present invention combines failure modes and numerical calculations, and can establish a random fatigue life curve of a sandwich structure by only conducting random fatigue tests under a single stress level, which can then be used to predict the shear fatigue life under different vibration levels. It has the advantages of requiring fewer test data points, reducing test costs, and improving calculation efficiency.

[0022] Specifically, the method for determining the shear fatigue life curve of a sandwich structure under random excitation provided by the present invention comprises the following steps.

[0023] Step A, carrying out a fatigue life test under a certain random vibration load on a sandwich structure test piece, and obtaining the time when a shear crack appears under the load, that is, the random fatigue life t0 under the load;

[0024] Step B, establish a dynamic response numerical analysis model consistent with the sandwich structure test piece in the finite element software, keep the boundary conditions and load levels consistent with the test, that is, fix the connection holes on both sides of the test piece fixture, and solve the random vibration load spectrum used in the model loading test to obtain the interlayer shear root mean square stress of the sandwich structure under the random load. Specifically, the boundary conditions refer to the fixing of the connection holes on both sides of the test piece fixture, and the loading conditions refer to the random vibration load spectrum used in the loading test.

[0025] Step C, based on the interlaminar shear root mean square stress of the sandwich structure Calculate the peak interlaminar shear stress under narrowband excitation The implementation process of solving the peak interlaminar shear stress under narrowband excitation in step C is as follows: the peak stress under narrowband excitation is known. RMS stress The ratio is about 2.5 to 3.5, and the peak interlaminar shear stress level is approximately:

[0026]

[0027] Among them, α is the ratio of the peak interlaminar shear stress under narrowband excitation to the interlaminar shear root mean square stress of the sandwich structure. In engineering approximate estimation, a larger value is generally taken, and the calculation result is conservative. Therefore, α is generally 3.5, that is,

[0028] Step D, establish a dual-parameter interlaminar shear fatigue life model under R=-1 equal amplitude fatigue condition:

[0029] τ 13 =τ ult t -1 / β (2)

[0030] Among them, τ 13 is the peak stress level of interlaminar shear static fatigue test, which is different from the peak interlaminar shear stress under narrow band excitation. Horizontal correspondence, t is fatigue life, τ ult is the interlaminar shear static strength of the sandwich material, that is, the peak stress when the fatigue cycle is t=0. The interlaminar shear static strength of the sandwich material is usually provided by the material manufacturer as a known quantity; β is a fitting constant related to the material.

[0031] Step E, solving the material-related fitting constant β in the life model; the implementation process of solving the material-related fitting constant β in the life model in step E is: substituting the random fatigue life t0 obtained in step A into the parameter t of formula (2), substituting the peak interlaminar shear stress obtained in step C into Substituting the parameter τ into formula (2) 13 , substitute the interlaminar shear static strength τ provided by the material manufacturer ult , the value of β can be obtained by solving;

[0032] Step F, establishing a random fatigue life curve; the implementation process of establishing the random fatigue life curve in step F is: based on the relationship between the root mean square stress and the peak stress in formula (1) and the relationship between the peak stress and the fatigue life in formula (2), the relationship between the root mean square stress and the fatigue life is solved as shown in formula (3), the β value obtained in step E is substituted into formula (3), and formula (3) is plotted into a curve, which is the shear root mean square stress and fatigue life curve under random load.

[0033]

[0034] When α is 3.5,

[0035] According to another aspect of the present invention, a system for determining a shear fatigue life curve under random excitation of a sandwich structure is provided. The system for determining a shear fatigue life curve under random excitation of a sandwich structure uses the method for determining a shear fatigue life curve under random excitation of a sandwich structure as described above to determine a shear fatigue life curve.

[0036] By applying this configuration, a system for determining the shear fatigue life curve under random excitation of a sandwich structure is provided. The system is based on the proportional relationship between the peak stress and the root mean square stress of the response under narrowband excitation, and the narrowband random stress is equivalent to a constant amplitude stress load. In combination with failure modes and numerical calculations, a random fatigue life curve can be established by only conducting random fatigue tests under a single stress level. The fatigue life curve can be used to predict the crack initiation life when a sandwich structure fails in rapid shear fatigue under random basic excitation loads of different magnitudes. Compared with existing solutions, the present invention combines failure modes and numerical calculations, and can establish a random fatigue life curve of a sandwich structure by only conducting random fatigue tests under a single stress level, which can then be used to predict the shear fatigue life under different vibration levels. It has the advantages of requiring fewer test data points, reducing test costs, and improving calculation efficiency.

[0037] In order to further understand the present invention, the following Figures 1 to 3 The method for determining the shear fatigue life curve of the sandwich structure under random excitation provided by the present invention is described in detail.

[0038] like Figures 1 to 3 As shown, according to a specific embodiment of the present invention, a method for determining a shear fatigue life curve under random excitation of a sandwich structure is provided, which is specifically implemented as follows:

[0039] 1. Carry out a random vibration load fatigue life test of 5g total root mean square level for the sandwich structure test piece, and carry out the same level test for 3 specimens, and take the median random fatigue life t0=1000s under this load;

[0040] 2. Establish a dynamic response numerical analysis model consistent with the sandwich structure test piece (such as Figure 2 As shown in the figure, the boundary conditions and load levels are kept consistent with the test, and then the root mean square stress between the layers of the sandwich material under the random load is obtained according to the root mean square stress cloud diagram obtained by the solution.

[0041] 3. Solve the peak interlaminar shear stress under narrowband excitation

[0042] 4. Establish a dual-parameter interlaminar shear fatigue life model under R=-1 equal amplitude fatigue conditions:

[0043] τ 13=τ ult t -1 / β (2)

[0044] Among them, τ 13 is the peak stress level of the interlaminar shear static fatigue test, corresponding to the peak interlaminar shear stress level under narrowband excitation, t is the fatigue life, τ ult is the interlaminar shear static strength of the sandwich material, that is, the peak stress when the fatigue cycle is t=0. The interlaminar shear static strength of the sandwich material is usually provided by material units as a known quantity; β is a fitting constant related to the material.

[0045] 5. Substitute the random fatigue life t0=1000s obtained from the experiment into the parameter t in formula (2) and calculate the peak interlaminar shear stress obtained after numerical analysis and processing. Substituting the parameter τ into formula (2) 13 , and finally substitute the interlaminar shear static strength τ provided by the material manufacturer ult =1MPa, and we can solve for β=5.45;

[0046] 6. Based on the relationship between the root mean square stress and the peak stress in formula (1) and the relationship between the peak stress and the fatigue life in formula (2), the relationship between the root mean square stress and the fatigue life is obtained as shown in formula (3). Substitute the β value obtained in step E into formula (3) and draw formula (3) into a curve (as shown in Figure 3 (as shown) is the shear root mean square stress and fatigue life curve under random load.

[0047]

[0048] The present invention proposes a method for determining a shear fatigue life curve under random excitation of a sandwich structure. Based on the proportional relationship between the peak stress and the root mean square stress of the response under narrowband excitation, the narrowband random stress is equivalent to a constant amplitude stress load. Combining failure modes and numerical calculations, a random fatigue life curve can be established by only conducting random fatigue tests under a single stress level. The fatigue life curve can be used to predict the crack initiation life when a sandwich structure fails in rapid shear fatigue under random basic excitation loads of different magnitudes.

[0049] The present invention combines failure modes and numerical calculations, and can establish a random fatigue life curve of a sandwich structure by only conducting random fatigue tests under a single stress level, which can then be used to predict shear fatigue life under different vibration levels. It has the advantages of requiring fewer test data points, reducing test costs, and improving calculation efficiency.

[0050] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0051] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining shear fatigue life curve under random excitation of a sandwich structure, characterized in that: The method for determining the shear fatigue life curve under random excitation of the sandwich structure comprises: Step 1: Conduct fatigue life test under a random vibration load on the sandwich structure test piece to obtain the shear crack appearance time under the load, that is, the random fatigue life t0 under the load; Step 2: Establish a dynamic response numerical analysis model consistent with the sandwich structure test piece in the finite element software, keep the boundary conditions and load levels consistent with the test, and solve the interlaminar shear root mean square stress of the sandwich structure under the random load. Step 3: According to the interlaminar shear root mean square stress of the sandwich structure Calculate the peak interlaminar shear stress under narrowband excitation Step 4, establish a dual-parameter interlaminar shear fatigue life model under R=-1 equal amplitude fatigue condition; Step 5: The peak interlaminar shear stress under narrowband excitation The peak stress level τ of interlaminar shear static fatigue test 13 Correspondingly, the random fatigue life t0 and the peak interlaminar shear stress under narrowband excitation are And interlaminar shear static strength τ ult Substitute it into the two-parameter interlaminar shear fatigue life model and calculate the fitting constant β related to the material; Step six, substituting the material-related fitting constant β into the dual-parameter interlaminar shear fatigue life model and plotting it into a curve to obtain a shear root mean square stress and fatigue life curve under random load.

2. The method for determining the shear fatigue life curve under random excitation of a sandwich structure according to claim 1, characterized in that: In the step 2, the boundary condition refers to the fixing of the connection holes on both sides of the test piece fixture, and the loading condition refers to the random vibration load spectrum used in the loading test.

3. The method for determining the shear fatigue life curve under random excitation of a sandwich structure according to claim 1, characterized in that: In step 3, the peak interlaminar shear stress under narrowband excitation is According to Wherein, α is the ratio of the peak interlaminar shear stress under narrow-band excitation to the interlaminar shear root mean square stress of the sandwich structure, and the value of α is 2.5 to 3.

5.

4. The method for determining the shear fatigue life curve under random excitation of a sandwich structure according to claim 3, characterized in that: The dual-parameter interlaminar shear fatigue life model is τ 13 =τ ult t -1 / β , where τ 13 is the peak stress level of interlaminar shear static fatigue test, t is the fatigue life, τ ult is the interlaminar shear static strength of the sandwich material, and β is a fitting constant related to the material.

5. The method for determining shear fatigue life curve under random excitation of a sandwich structure according to claim 4, characterized in that: The shear root mean square stress and fatigue life curve under random load is based on Calculate acquisition.

6. The method for determining the shear fatigue life curve under random excitation of a sandwich structure according to claim 5, characterized in that: The ratio α of the peak interlaminar shear stress under the narrowband excitation to the interlaminar shear root mean square stress of the sandwich structure is 3.

5.

7. A system for determining shear fatigue life curves under random excitation of sandwich structures, characterized in that: The system for determining a shear fatigue life curve under random excitation of a sandwich structure uses the method for determining a shear fatigue life curve under random excitation of a sandwich structure as described in claims 1 to 6 to determine a shear fatigue life curve.

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