Fatigue test equipment and test sample S-N curve acquisition method

Abstract

The invention provides fatigue test equipment and a test sample S-N curve obtaining method, and relates to the technical field of material or part dynamic stress-fatigue life prediction.The fatigue test equipment comprises a vibration assembly suitable for assembling the first end of a to-be-detected test sample, the second end, far away from the first end, of the test sample piece is suspended outside the vibration assembly, so that an input load in the first direction is applied to the test sample piece; the counterweight assembly is detachably arranged at the second end so as to adjust the bending stress of the test sample piece; and the detection assembly is suitable for at least monitoring the strain of a stress calibration point, a stress control point and a stress monitoring point arranged on the test sample piece.

Description

Technical Field

[0001] The present disclosure relates to the technical field of dynamic stress-fatigue life prediction of materials or parts, and more specifically, to a fatigue test device and a method for obtaining SN curves of test samples. Background Art

[0002] The SN curve, also known as the fatigue curve, is a curve used to describe the relationship between the number of cycles (N) required for a material to reach fatigue failure under alternating stress and the stress level (σ), so as to reflect the number of cycles that the material can withstand under different stress levels.

[0003] At present, the test for obtaining SN curve generally adopts tension and compression test or three-point bending test. The above test method belongs to quasi-static method, and the loading frequency is generally controlled at 5-10Hz. This will lead to a long test cycle and fail to reflect the influence of the natural frequency of the structure on fatigue damage.

[0004] On this basis, the vibration test method can also be used to apply input loads to the test specimens by controlling the acceleration load to shorten the test cycle. From the test data analysis, as the fatigue damage of the test specimens accumulates, the structural natural frequency of the test specimens will change, which will cause the mapping relationship between the acceleration load and the stress response to change. Therefore, the use of the acceleration load control method to obtain the structural SN curve is quite different from the actual situation. Summary of the invention

[0005] In view of this, the present disclosure provides a fatigue test device and a method for obtaining the SN curve of a test sample. By suspending the test sample on a vibration component, the loading frequency of the test process can be effectively increased to shorten the test cycle. In addition, based on the detection components configured on the stress calibration points, stress control points and stress monitoring points of the test sample, the stress can be monitored and the stress can be maintained unchanged during the test, thereby improving the stress control accuracy.

[0006] One aspect of the present disclosure provides a fatigue testing device, comprising: a vibration assembly, suitable for assembling a first end of a test specimen to be tested, and suspending a second end of the test specimen away from the first end outside the vibration assembly to apply an input load along a first direction to the test specimen; a weight assembly, detachably disposed at the second end to adjust the bending stress of the test specimen; and a detection assembly, suitable for monitoring the strain of at least a stress calibration point, a stress control point and a stress monitoring point disposed on the test specimen.

[0007] According to an embodiment of the present disclosure, the fatigue testing equipment further includes an acceleration detection component, which is suitable for monitoring the input load of the vibration component along the first direction.

[0008] According to an embodiment of the present disclosure, the stress calibration point, the stress control point and the stress monitoring point are sequentially arranged on the test sample from the first end to the second end.

[0009] According to an embodiment of the present disclosure, the detection component includes at least three strain gauges, and the three strain gauges are respectively arranged at the stress calibration point, the stress control point and the stress monitoring point.

[0010] According to an embodiment of the present disclosure, the loading frequency of the input load applied by the vibration assembly to the test sample is the natural frequency of the test sample.

[0011] Another aspect of the present disclosure also provides a method for obtaining an SN curve of a test specimen based on a fatigue test device, comprising: designing a test specimen and establishing a first finite element model of the test specimen; obtaining stress calibration points and stress control points of the test specimen based on the first finite element model; assembling the test specimen on the fatigue test device, and obtaining stress monitoring points based on the stress control points and preset spacings; respectively setting strain gauges at the stress calibration points, the stress control points and the stress monitoring points, and applying an input load to the test specimen at a fixed frequency to obtain the number of fatigue cycles of the test specimen; and forming an SN curve of the test specimen based on the number of fatigue cycles and stress levels.

[0012] According to an embodiment of the present disclosure, the above-mentioned method of obtaining stress calibration points and stress control points of the above-mentioned test specimen based on the above-mentioned first finite element model includes: configuring the stress state and constraint conditions of the above-mentioned test specimen based on the above-mentioned first finite element model to obtain stress calibration points and fatigue danger areas; and further processing the above-mentioned first finite element model to form a second finite element model with cracks in the above-mentioned fatigue danger area, and obtaining stress control points.

[0013] According to an embodiment of the present disclosure, the stress state and constraint conditions of the test specimen configured based on the first finite element model are used to obtain the stress calibration point and the fatigue danger zone, including: establishing a geometric model according to the size and shape of the test specimen; meshing the geometric model to form the first finite element model, and defining the material properties of the test specimen; and setting the stress state and constraint conditions to perform stress response analysis, using the identified maximum stress occurrence position as the stress calibration point, and using the portion between the stress calibration point and the second end as the fatigue danger zone.

[0014] According to an embodiment of the present disclosure, the first finite element model is further processed to form a second finite element model with cracks in the fatigue risk area, and the stress control point is obtained, including: simulating the crack occurrence position to the fatigue risk area, and configuring the crack path to simulate the crack expansion to form the second finite element model; selecting an observation area between the crack occurrence position and the second end, and setting a plurality of observation units in the observation area; and applying a unit load to the second finite element model, and identifying the critical position where the stress change is not obvious as the stress control point by comparing the absolute value difference of the stress between the upper surface and the lower surface of the test specimen.

[0015] According to an embodiment of the present disclosure, the test specimen is mounted on the fatigue test equipment, and stress monitoring points are obtained based on the stress control points and preset spacings, including: connecting the first end of the test specimen to a vibration assembly of the fatigue test equipment, and suspending the second end of the test specimen outside the vibration assembly; mounting a counterweight assembly on the second end; and obtaining stress monitoring points between the stress control point and the second end based on a preset spacing.

[0016] According to an embodiment of the present disclosure, strain gauges are respectively set at the stress calibration points, the stress control points and the stress monitoring points, and input loads are applied to the test specimens at a fixed frequency to obtain the number of fatigue cycles of the test specimens, including: strain gauges are respectively set at the stress calibration points, the stress control points and the stress monitoring points; the input loads are applied according to the natural frequency and vibration mode of the test specimens; the stress detection values ​​of the stress control points are obtained, and the input loads are maintained unchanged at a fixed frequency according to the stress calibration coefficients of the stress calibration points and the stress control points; and the stress responses of the stress monitoring points are obtained, and rain flow cycle counting is performed to obtain the number of fatigue cycles of the test specimens.

[0017] According to a fatigue test device and a method for obtaining the SN curve of a test sample provided by the present disclosure, by suspending the test sample on a vibration component, the loading frequency of the test process can be effectively increased to shorten the test cycle. During the test, by establishing a second finite element model containing a crack, the stress effect of the crack on the observation unit is analyzed, and the critical position where the crack has no obvious effect on the stress change is determined, and used as the stress control point. In addition, the stress calibration coefficient between the stress calibration point and the stress control point is further determined.

[0018] On this basis, based on the detection components configured at the stress calibration points, stress control points and stress monitoring points of the test specimen, stress changes can be monitored in real time during the test, and the stress can be controlled to remain basically unchanged, thereby improving the stress control accuracy of the test specimen during the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0020] Figure 1 A schematic diagram of a fatigue testing device according to an embodiment of the present disclosure is shown; and

[0021] Figure 2 The flowchart schematically shows a method for obtaining SN curve of a test sample based on fatigue testing equipment.

[0022] In the drawings, the meanings of the reference numerals are as follows:

[0023] 1. Test equipment;

[0024] 11. Vibration components;

[0025] 12. Workwear;

[0026] 13. Counterweight assembly;

[0027] 14. Detection components;

[0028] 141, first strain gauge;

[0029] 142. Second strain gauge;

[0030] 143. a third strain gauge; and

[0031] 2. Test samples. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0033] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0034] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0035] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0036] Figure 1 A principle diagram of a fatigue testing device according to an embodiment of the present disclosure is schematically shown.

[0037] The embodiment of the present disclosure provides a fatigue test device, such as Figure 1 As shown, it includes a vibration assembly 11, a weight assembly 13 and a detection assembly 14. The vibration assembly 11 is suitable for assembling the first end of the test sample 2 to be tested, and the second end of the test sample 2 away from the first end is suspended outside the vibration assembly 11 to apply an input load along a first direction to the test sample 2. The weight assembly 13 is detachably arranged at the second end to adjust the bending stress of the test sample 2. The detection assembly 14 is suitable for monitoring the strain of at least the stress calibration point, the stress control point and the stress monitoring point arranged on the test sample 2.

[0038] In an illustrative embodiment, Figure 1 As shown, the test sample 2 includes but is not limited to being constructed as a plate-like structure. In detail, the test sample 2 of the plate-like structure includes but is not limited to being constructed as a dumbbell-shaped structure with wide ends (the wider ends are used to connect the vibration component 11 and the counterweight component 13 respectively) and a narrow middle part (the narrower middle part is used to set stress calibration points, stress control points and stress monitoring points). Among them, the test sample 2 can not only be used for structural research of certain components of rail vehicles (such as bogies), but also can be applied to other structures outside rail vehicles, and has a large engineering application scenario.

[0039] In an illustrative embodiment, Figure 1 As shown, the test specimen 2 includes a first end (such as Figure 1 left end as shown) and the second end (as shown Figure 1The right end as shown). In detail, a first mounting hole is provided on the first end (covered by the tooling 12 and not shown), and a second mounting hole is provided on the second end (covered by the tooling 12 and not shown). The first mounting hole includes but is not limited to two holes configured to be axially symmetrical, so as to be symmetrically mounted on the vibration assembly 11, thereby limiting the displacement of the test specimen 2 relative to the vibration assembly 11 and preventing the adverse effects of structural overload on the test; the second mounting hole is provided in the middle of the second end, so that the gravity of the configured counterweight assembly 13 is more evenly distributed on the second end. Furthermore, the tooling 12 for connecting the test specimen 2 with the vibration assembly 15 and / or the counterweight assembly 13 includes but is not limited to bolts, and the counterweight applied by the counterweight assembly 13 can be non-continuously adjusted by the number of assembled counterweights to meet the counterweight requirements described in the test.

[0040] In such an embodiment, the test specimen 2 is suspended on the vibration assembly 11, and the vibration assembly 11 is suitable for applying an input load along a first direction (i.e., up and down direction) to the first end of the test specimen 2, and the second end of the test specimen 2 extends outside the vibration assembly 11 to vibrate along the up and down direction in response to the fluctuation of the first end, thereby forming a cycle in the bending test. In this process, the second end of the test specimen 2 has the freedom to vibrate up and down, so its structural force can be regarded as bending stress. Compared with the current tension and compression test or three-point bending test, the loading frequency can be greatly increased (such as the loading frequency can reach 80Hz and above), thereby shortening the test cycle; and the bending degree of the test specimen 2 can also be controlled by controlling the input load (stress).

[0041] On this basis, based on the detection component 14 configured at the stress calibration points, stress control points and stress monitoring points of the test sample (the acquisition and function of the stress calibration points, stress control points and stress monitoring points will be described in detail in the following method section), the stress can be monitored, and the vibration component 11 can be controlled during the test to maintain the stress of the test sample 2 unchanged during the test, thereby improving the stress control accuracy.

[0042] In an illustrative embodiment, not shown in the figure, the vibration assembly 11 includes but is not limited to an electromagnetic vibration test bench. Further, the electromagnetic vibration test bench is also equipped with a collection system for collecting signals (such as analog signals and / or digital signals) required for the test, and a control system suitable for controlling the input load of the electromagnetic vibration test bench.

[0043] It should be noted here that the (electromagnetic) vibration test bench is not the key point of protection of the present disclosure, and any vibration test bench in the art that can be used to provide input loads in the up and down directions for the test sample 2 can be selected and applied, and no further details will be given.

[0044] According to an embodiment of the present disclosure, not shown in the figure, the fatigue test equipment further includes an acceleration detection component 14. The acceleration detection component 14 is suitable for monitoring the input load of the vibration component 11 along the first direction.

[0045] In an illustrative embodiment, the acceleration detection component 14 includes but is not limited to using an acceleration sensor. In detail, the acceleration sensor can be set on the test sample 2, such as being set on at least one of the fatigue risk area, the stress control point and the second end, so as to monitor the input load of the vibration component 11 through the vibration response of the corresponding part, so as to assist in statistics and calculation of the influence of the cumulative damage of structural fatigue on the mode.

[0046] According to an embodiment of the present disclosure, not shown in the figure, the stress calibration points, stress control points and stress monitoring points are sequentially arranged on the test sample 2 from the first end to the second end.

[0047] According to the embodiments of the present disclosure, Figure 1 As shown, the detection assembly 14 includes at least three strain gauges. The three strain gauges are respectively arranged at a stress calibration point, a stress control point and a stress monitoring point.

[0048] In an illustrative embodiment, Figure 1 As shown, the detection assembly 14 includes but is not limited to three strain gauges, namely a first strain gauge 141, a second strain gauge 142 and a third strain gauge 143. In detail, the first strain gauge 141 covers the stress calibration point, the second strain gauge 142 covers the stress control point, and the third strain gauge 143 covers the stress monitoring point.

[0049] In an exemplary embodiment, the stress calibration point and the stress control point ( Figure 1 The detected component, i.e., the strain gauge covered (not shown) is obtained by, but not limited to, the following method. Further, the stress monitoring point ( Figure 1 The detected component, that is, the strain gauge covered (not shown), includes but is not limited to obtaining the stress control points based on the obtained stress control points by preset spacing (described in detail in the method below).

[0050] According to the embodiments of the present disclosure, Figure 1 As shown, the loading frequency of the input load applied by the vibration component 11 to the test sample 2 is the natural frequency of the test sample 2.

[0051] In such an embodiment, the input load applied by the vibration component 11 to the test sample 2 should be configured to be substantially the same as the natural frequency (i.e., modal frequency) of the test sample 2, which is conducive to making the test sample 2 reach a resonant state, thereby obtaining a larger vibration amplitude through a smaller input load. In this way, the output energy of the vibration component 11 (such as an electromagnetic vibration test bench) can be greatly reduced, the wear of the vibration component 11 itself can be reduced, and its service life can be extended.

[0052] Figure 2 The flowchart schematically shows a method for obtaining SN curve of a test sample based on fatigue testing equipment.

[0053] The embodiment of the present disclosure provides a method for obtaining the SN curve of a test sample based on a fatigue test device 1, such as Figure 2 As shown, including:

[0054] Operation S100: designing a test sample and establishing a first finite element model of the test sample.

[0055] Operation S110: Acquire stress calibration points and stress control points of the test sample based on the first finite element model.

[0056] Operation S120: assembling the test sample on the fatigue test equipment, and obtaining stress monitoring points according to the stress control points and the preset intervals.

[0057] Operation S130: strain gauges are respectively set at the stress calibration point, the stress control point, and the stress monitoring point, and input loads are applied to the test sample at a fixed frequency to obtain the number of fatigue cycles of the test sample.

[0058] Operation S140: generating an SN curve of the test sample based on the number of fatigue cycles and the stress level.

[0059] In such an implementation, by establishing a second finite element model containing a crack, the stress effect of the crack on the observation unit is analyzed, and the critical position where the crack has no obvious effect on the stress change is determined, and used as the stress control point. In addition, the stress calibration coefficient between the stress calibration point and the stress control point is further determined. On this basis, based on the detection components configured at the stress calibration point, stress control point and stress monitoring point of the test sample, the stress change can be monitored in real time during the test process, and the stress can be controlled to remain basically unchanged, thereby improving the stress control accuracy of the test sample during the test process.

[0060] In an exemplary embodiment, operation S100: designing a test sample and establishing a first finite element model of the test sample includes:

[0061] Operation S101: Based on the interface of the vibration component 11 (such as an electromagnetic vibration test bench), a test sample 2 of a plate-like structure is designed to have a first end (which can be regarded as a fixed end) and a second end (which can be regarded as a cantilever end).

[0062] The first end needs to be provided with a first mounting hole according to the interface of the vibration component 11 (such as an electromagnetic vibration test bench), and the second end needs to be provided with a second mounting hole according to the configured counterweight component 13 .

[0063] Operation S102: obtaining corresponding outer dimensions (such as a dumbbell-shaped plate structure), internal structure, holes (such as a first mounting hole and a second mounting hole), and chamfers (such as a chamfer formed by a first end and a second end) based on the designed test sample 2.

[0064] Operation S103: selecting a suitable mesh type and mesh size according to the structural characteristics and analysis requirements of the test sample 2, and performing mesh division to establish a first finite element model.

[0065] According to an embodiment of the present disclosure, operation S110: acquiring stress calibration points and stress control points of the test sample based on the first finite element model includes:

[0066] Operation S111: configuring the stress state and constraint conditions of the test specimen based on the first finite element model to obtain stress calibration points and fatigue risk areas.

[0067] The above operation S111: obtaining stress calibration points and fatigue risk areas based on the stress state and constraint conditions of the test specimen configured by the first finite element model includes:

[0068] Operation S1111: Establishing a geometric model according to the size and shape of the test sample.

[0069] Operation S1112: Meshing the geometric model to form a first finite element model, and defining material properties of the test sample;

[0070] The material properties include but are not limited to at least one of elastic modulus, Poisson's ratio, density, and yield strength.

[0071] Operation S1113: setting the stress state and constraint conditions to perform stress response analysis, taking the identified maximum stress occurrence position as the stress calibration point, and taking the portion between the stress calibration point and the second end as the fatigue risk area.

[0072] The stress state includes but is not limited to at least one of externally applied concentrated force, distributed force pressure, bending moment and torque; the constraint conditions include but are not limited to applying corresponding displacement constraints (such as fixed, sliding and swinging, etc.) and / or rotation constraints on the first finite element model according to the actual fixing method (i.e., suspension) of the test sample 2.

[0073] On this basis, finite element analysis is run to calculate the stress response under unit load and identify the location where the maximum stress occurs, so that the location where the maximum stress occurs on the test specimen 2 is used as the stress calibration point, and the portion between the stress calibration point and the second end is used as the fatigue risk area.

[0074] In addition, the natural frequency and vibration mode of the test sample 2 are determined by modal separation of the first finite element model as a basis for subsequent input loads. It should be understood that the established first finite element model should ensure that the stress distribution and displacement are reasonable. If necessary, the model parameters and / or mesh of the first finite element model need to be adjusted to re-analyze.

[0075] Operation S112: further processing the first finite element model to form a second finite element model having cracks in the fatigue risk area, and obtaining stress control points.

[0076] According to an embodiment of the present disclosure, operation S112: further processing the first finite element model (i.e., based on the stress analysis structure of the first finite element model, performing secondary processing on the first finite element model to obtain a second finite element model), forming a second finite element model having cracks in the fatigue risk area, and obtaining stress control points includes:

[0077] Operation S1121: simulating the crack occurrence position to the fatigue risk area, and configuring the crack path to simulate the crack propagation to form a second finite element model;

[0078] Specifically, it includes geometrically defining cracks in the fatigue risk area and creating at least one crack. If multiple cracks with different depths are created, the interval depth between different cracks includes but is not limited to being configured as 2 mm (millimeter), and the maximum crack depth is configured as 0.8 times the thickness of the test sample 2 to ensure that the crack does not penetrate the entire test sample 2;

[0079] Further, including but not limited to using separate elements to simulate cracks in the first finite element model, these separate elements are set on a predetermined crack path to simulate the expansion of the crack, for example, the portion of the crack close to the upper surface is wider than the portion close to the lower surface.

[0080] Operation S1122: selecting an observation area between the crack occurrence position and the second end, and setting a plurality of observation units in the observation area;

[0081] Specifically, an area including but not limited to 20 mm (millimeter) is selected from the upper and lower surfaces of the test sample 2 along the direction from the crack position to the second end as the observation area.

[0082] Operation S1123: applying a unit load to the second finite element model, and identifying a critical position where the stress change is not obvious as a stress control point by comparing the absolute value difference of the stress between the upper surface and the lower surface of the test sample.

[0083] Specifically, it includes running a finite element analysis after applying a unit load to calculate the response of the crack depth change to the stress and recording the change pattern of the stress of the observation unit with the crack depth; in addition, the stress units at the same position on the upper and lower surfaces are compared. When the absolute value difference of the stress units at the same position on the upper and lower surfaces extending from the stress calibration point to the second end is zero for the first time, the position is regarded as a critical position where the stress change is not obvious, and is used as a stress control point.

[0084] According to an embodiment of the present disclosure, operation S120: assembling the test sample on the fatigue test equipment, and obtaining the stress monitoring point according to the stress control point and the preset interval includes:

[0085] Operation S121: connecting a first end of the test sample to a vibration assembly of a fatigue test device, and suspending a second end of the test sample outside the vibration assembly;

[0086] Operation S122: assembling the counterweight assembly on the second end;

[0087] Specifically, the test sample 2 is assembled on the vibration component 11, and a counterweight component 13 of suitable weight is arranged on the second end of the test sample 2 extending outside the vibration component 11, wherein the test sample 2 should be symmetrically arranged at the structural position of the vibration component 11 to avoid the influence caused by structural unbalanced loading.

[0088] Operation S123: acquiring a stress monitoring point between the stress control point and the second end according to a preset interval.

[0089] Specifically, a preset spacing of 20 mm (millimeter) is used as a stress monitoring point at the second end from the stress control point. It should be understood that the preset spacing includes but is not limited to being configured as the above-mentioned 20 mm, and can be specifically configured based on empirical values ​​and / or calculated values.

[0090] According to an embodiment of the present disclosure, operation S130: respectively setting strain gauges at the stress calibration point, the stress control point and the stress monitoring point, and applying input load to the test sample at a fixed frequency to obtain the number of fatigue cycles of the test sample includes:

[0091] Operation S131: setting strain gauges at the stress calibration point, the stress control point and the stress monitoring point respectively;

[0092] Specifically, a first strain gauge 141 is arranged at the stress calibration point, a second strain gauge 142 is arranged at the stress control point, and a third strain gauge 143 is arranged at the stress monitoring point, wherein the strain gauges include but are not limited to being bonded to corresponding points.

[0093] Operation S132: applying an input load according to the natural frequency and vibration mode of the test sample;

[0094] Specifically, it includes applying an input load that is adapted to the natural frequency and vibration mode obtained in operation S1113 (substantially the same as the natural frequency and vibration mode), so as to make the test sample 2 and the vibration component 11 form resonance as much as possible during the vibration test.

[0095] Operation S133: obtaining a stress detection value of the stress control point, and maintaining the input load unchanged at a fixed frequency according to the stress calibration point and the stress calibration coefficient of the stress control point;

[0096] Specifically, the calibration coefficient (i.e., transfer coefficient) of the stress calibration point and the stress control point of the test sample 2 is determined by using a sine frequency sweep test or a fixed frequency loading test, and the maximum value of the loading frequency is determined in the sine frequency sweep test. Before the maximum loading frequency is reached, the range of the loading frequency will not affect the corresponding relationship between the stress calibration point and the stress control point (i.e., calibration coefficient). To this end, it can be obtained based on the strain value feedback detected by the stress control point whether the input load applied by the stress calibration point is in a basically constant state (which can be regarded as the stress remaining unchanged).

[0097] For example, taking the embodiment with a calibration coefficient of 0.895 as an example, if the actual stress detected at the stress control point is 284 MPa, the input load applied by the vibration component should be 320 MPa. In this way, the stress at the stress control point can be maintained unchanged during the entire test process, thereby overcoming the change in the mapping relationship between the acceleration load and the stress response caused by the accumulation of fatigue damage of the test sample, thereby improving the stress control accuracy of the test sample during the test process.

[0098] Operation S134: obtaining the stress response of the stress monitoring point and performing rain flow cycle counting to obtain the number of fatigue cycles of the test sample;

[0099] Specifically, when the input load is basically constant, by collecting the stress response of the stress monitoring point and performing rain flow cycle counting (i.e., tower top technology), the number of complete cycles and half cycles in the entire input load history can be obtained based on the load-time curve (i.e., a curve with the load coordinate axis as the horizontal axis and the time coordinate axis transformation as the vertical axis multiplied by the load coordinate axis), and then the number of fatigue cycles of the test sample 2 can be obtained.

[0100] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A fatigue testing device, characterized in that: include: A vibration assembly (11) adapted to be assembled with a first end of a test sample (2) to be tested, and to suspend a second end of the test sample (2) away from the first end outside the vibration assembly (11) so as to apply an input load along a first direction to the test sample (2); A weight assembly (13) detachably disposed at the second end to adjust the bending stress of the test specimen (2); as well as The detection component (14) is suitable for monitoring the strain of at least a stress calibration point, a stress control point and a stress monitoring point arranged on the test sample (2).

2. The device according to claim 1, characterized in that It also includes an acceleration detection component (14) suitable for monitoring the input load of the vibration component (11) along the first direction.

3. The device according to claim 1 or 2, characterized in that The stress calibration points, the stress control points and the stress monitoring points are arranged on the test sample (2) in sequence and spaced from the first end to the second end.

4. The device according to claim 3, characterized in that The detection component (14) comprises at least three strain gauges, and the three strain gauges are respectively arranged at the stress calibration point, the stress control point and the stress monitoring point.

5. The device according to claim 1 or 2, characterized in that The loading frequency of the input load applied by the vibration component (11) to the test sample (2) is the natural frequency of the test sample (2).

6. A method for obtaining SN curve of a test sample based on the test equipment according to any one of claims 1 to 5, characterized in that: include: Designing a test sample and establishing a first finite element model of the test sample; Acquire stress calibration points and stress control points of the test sample based on the first finite element model; Assembling the test specimen on the fatigue test equipment, and obtaining stress monitoring points according to the stress control points and the preset intervals; Strain gauges are respectively arranged at the stress calibration point, the stress control point and the stress monitoring point, and input loads are applied to the test sample at a fixed frequency to obtain the number of fatigue cycles of the test sample; An SN curve of the test specimen is formed based on the fatigue cycle number and the stress level.

7. The method according to claim 6, characterized in that The step of obtaining the stress calibration points and stress control points of the test sample based on the first finite element model includes: Configuring the stress state and constraint conditions of the test specimen based on the first finite element model to obtain stress calibration points and fatigue risk areas; and The first finite element model is further processed to form a second finite element model having cracks in the fatigue risk area, and a stress control point is obtained.

8. The method according to claim 7, characterized in that The step of configuring the stress state and constraint conditions of the test specimen based on the first finite element model to obtain stress calibration points and fatigue risk areas includes: Establishing a geometric model according to the size and shape of the test sample; Meshing the geometric model to form the first finite element model and defining material properties of the test specimen; and The stress state and constraint conditions are set to perform stress response analysis, the identified maximum stress occurrence position is used as the stress calibration point, and the part between the stress calibration point and the second end is used as the fatigue risk area.

9. The method according to claim 8, characterized in that The further processing of the first finite element model to form a second finite element model having cracks in the fatigue risk area and obtaining stress control points includes: Simulating the crack occurrence position to the fatigue risk area, and configuring the crack path to simulate the crack propagation to form a second finite element model; Selecting an observation area between the crack occurrence position and the second end, and setting a plurality of observation units in the observation area; and A unit load is applied to the second finite element model, and a critical position where the stress change is not obvious is identified as the stress control point by comparing the absolute value difference of the stress between the upper surface and the lower surface of the test sample.

10. The method according to any one of claims 7 to 9, characterized in that: The step of assembling the test specimen on the fatigue test equipment and obtaining stress monitoring points according to the stress control points and the preset intervals includes: Connecting a first end of the test specimen to a vibration assembly of a fatigue test device, and suspending a second end of the test specimen outside the vibration assembly; assembling a weight assembly on the second end; and A stress monitoring point is obtained between the stress control point and the second end according to a preset interval.

11. The method according to any one of claims 7 to 9, characterized in that: The step of respectively setting strain gauges at the stress calibration point, the stress control point and the stress monitoring point, and applying input load to the test sample at a fixed frequency to obtain the number of fatigue cycles of the test sample includes: Strain gauges are respectively arranged at the stress calibration point, the stress control point and the stress monitoring point; Applying the input load according to the natural frequency and vibration mode of the test specimen; Obtaining the stress detection value of the stress control point, and maintaining the input load unchanged at a fixed frequency according to the stress calibration point and the stress calibration coefficient of the stress control point; and The stress response of the stress monitoring point is obtained, and the rain flow cycle count is performed to obtain the fatigue cycle number of the test sample.

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