Microsample testing method for obtaining material fatigue performance based on wafer sample

Abstract

The invention discloses a micro-sample testing method for obtaining fatigue performance of a material based on a wafer sample, which comprises the following steps of: firstly, constructing equivalent stress and equivalent strain equations of a median point of the wafer sample, and further constructing a correlation equation between stress amplitude and strain amplitude of the wafer sample and the equivalent stress and equivalent strain of the median point under a fatigue test; performing multiple fatigue tests on the wafer sample under different displacement amplitudes to obtain a load-displacement lag curve and displacement amplitude, load amplitude and service life data, performing power law fitting on the load-displacement lag curve to obtain a material Hollomon law parameter of the wafer sample, and calculating the material Hollomon law parameter of the wafer sample according to a related equation. The displacement amplitude and the load amplitude are converted to obtain corresponding strain amplitude and stress amplitude, and finally, the Manson-Coffin law parameters of the material of the wafer sample are determined according to the strain amplitude, the stress amplitude and the life data. The method overcomes the defect that the fatigue performance micro-damage test on the small sample material is difficult to complete by the existing method.

Description

Technical Field

[0001] The invention belongs to the technical field of mechanical property testing of ductile metal materials, and in particular relates to the design of a micro-sample testing method for obtaining material fatigue properties based on a disc sample. Background Art

[0002] The fatigue performance of metal materials in service is an important part of structural safety design and life assessment. Due to objective conditions, the preparation of standard fatigue specimens often requires larger raw materials, and it is often difficult to obtain enough materials for processing traditional test specimens for in-service structural materials. Therefore, the fatigue performance test of materials faces many difficulties, and non-destructive testing methods and small specimen testing technology for material fatigue performance are in urgent need of development. At present, small specimen testing technology has made great progress in the uniaxial mechanical properties of materials and has formed many testing standards. However, small specimen testing methods for material fatigue performance still need to be further developed. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that it is currently difficult to complete micro-destructive testing of fatigue mechanical properties of service engineering materials. A micro-sample testing method for obtaining material fatigue properties based on disc specimens is proposed. The fatigue test based on micro-sample discs can simultaneously obtain the material's uniaxial stress-strain relationship (i.e., the material's Hollomon law) and fatigue properties (i.e., the Manson-Coffin law), which is of great significance to the field of material performance engineering testing.

[0004] The technical solution of the present invention is: a micro-sample testing method for obtaining material fatigue properties based on a disc sample, comprising the following steps:

[0005] S1. Construct the equivalent stress and equivalent strain equations of the midpoint of the disc specimen.

[0006] S2. Construct the correlation equation between the stress amplitude and strain amplitude of the disc specimen under fatigue test and the equivalent stress and equivalent strain of the midpoint.

[0007] S3. Perform multiple fatigue tests on the disc specimen at different displacement amplitudes to obtain the load-displacement hysteresis curve as well as displacement amplitude, load amplitude and life data.

[0008] S4. Perform power law fitting on the load-displacement hysteresis curve to obtain the Hollomon law parameters of the material of the disc specimen.

[0009] S5. According to the correlation equation, the displacement amplitude and load amplitude are converted into the corresponding strain amplitude and stress amplitude.

[0010] S6. Determine the Manson-Coffin law parameters of the material of the disc specimen based on the strain amplitude and life data.

[0011] Furthermore, the equivalent stress and equivalent strain equations of the midpoint of the disc sample in step S1 are specifically:

[0012]

[0013] where σ eq-C represents the equivalent stress at the midpoint, P represents the load, h represents the displacement, ε eq-C represents the equivalent strain at the midpoint, A * represents the characteristic area, h * represents characteristic displacement, k1, k2, k3 and k4 are model parameters of the equivalent stress and equivalent strain equation model at the midpoint of the disc specimen, k5 and k6 are intermediate parameters, and n represents the Hollomon law parameter of the material.

[0014] Furthermore, the correlation equation in step S2 is specifically:

[0015]

[0016] where σ a represents the stress amplitude, ε a represents the strain amplitude, e represents the natural constant, and a1, a2, a3, c1 and c4 are all model parameters of the associated equation model.

[0017] Furthermore, the iterative solution formula for the material Hollomon's law parameters in step S4 is:

[0018]

[0019] Where n and K are the Hollomon law parameters of the material, m represents the loading coefficient obtained by power law fitting of the load-displacement hysteresis curve, and C represents the loading index obtained by power law fitting of the load-displacement hysteresis curve.

[0020] Furthermore, the formula of the material Manson-Coffin law parameter in step S6 is:

[0021]

[0022] Where E represents the elastic modulus of the material, N f represents the life data, σ f ′、ε f ′, β and γ are all material Manson-Coffin law parameters.

[0023] The beneficial effects of the present invention are as follows: due to the limitation of sampling size, it is difficult to obtain the mechanical properties of service structural materials through traditional test methods, and thus the remaining life assessment of service components faces many challenges. In this context, the present invention is based on the established equivalent stress and equivalent strain equations for the midpoint of the disc specimen and the stress amplitude and strain amplitude equations for the specimen under fatigue test, and proposes a test method for determining the fatigue properties of materials based on tiny disc specimens, which makes up for the deficiency that existing methods are difficult to complete fatigue performance micro-damage testing of small sample materials, and has high engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure shows a flow chart of a micro-sample testing method for obtaining material fatigue properties based on a wafer specimen provided by an embodiment of the present invention.

[0025] Figure 2 Shown is a schematic diagram of finite element modeling provided by an embodiment of the present invention.

[0026] Figure 3 Shown is a schematic diagram of a wafer sample provided in an embodiment of the present invention.

[0027] Figure 4 The figure shows a wafer sample loading mechanism provided by an embodiment of the present invention.

[0028] Figure 5 Shown is a schematic diagram of a Hollomon's law verification curve for a material provided in an embodiment of the present invention.

[0029] Figure 6 Shown is a comparison chart of the fatigue life of the material provided by the embodiment of the present invention and the traditional test results. DETAILED DESCRIPTION

[0030] Now, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the accompanying drawings are only exemplary and are intended to explain the principles and spirit of the present invention, rather than to limit the scope of the present invention.

[0031] The embodiment of the present invention provides a micro-sample testing method for obtaining material fatigue properties based on a disc sample, such as Figure 1 As shown, the following steps S1 to S6 are included:

[0032] S1. Construct the equivalent stress and equivalent strain equations of the midpoint of the disc specimen.

[0033] In the embodiment of the present invention, the equivalent stress and equivalent strain equations of the midpoint of the disc specimen are specifically:

[0034]

[0035] where σ eq-Crepresents the equivalent stress at the midpoint, P represents the load, h represents the displacement, ε eq-C represents the equivalent strain at the midpoint, A * represents the characteristic area, h * represents characteristic displacement, k1, k2, k3 and k4 are model parameters of the equivalent stress and equivalent strain equation model at the midpoint of the disc specimen, k5 and k6 are intermediate parameters, and n represents the Hollomon law parameter of the material.

[0036] In the embodiment of the present invention, as an example, the values ​​of model parameters k1, k2, k3 and k4 are given in Table 1.

[0037] Table 1 Parameters of the equivalent stress and equivalent strain equation models

[0038]

[0039]

[0040] S2. Construct the correlation equation between the stress amplitude and strain amplitude of the disc specimen under fatigue test and the equivalent stress and equivalent strain of the midpoint.

[0041] In the embodiment of the present invention, the correlation equation is specifically:

[0042]

[0043] where σ a represents the stress amplitude, ε a represents the strain amplitude, e represents the natural constant, and a1, a2, a3, c1 and c4 are all model parameters of the associated equation model.

[0044] In the embodiment of the present invention, the model parameters a1, a2, a3, c1 and c4 can be determined by the following formula:

[0045]

[0046] where ε y represents the nominal yield strain, k = 1, 2, 3, s = 1, 2, 3, 4, b k1 , b k2 , b k3 , b k4 , b k5 ,d s1 ,d s2 ,d s3 ,d s4 and d s5 are all model parameters.

[0047] In the embodiment of the present invention, as an example, the model parameter b k1 , b k2 , bk3 , b k4 and b k5 The values ​​of are given in Table 2. The model parameter d s1 ,d s2 ,d s3 ,d s4 and d s5 The values ​​of are given in Table 3.

[0048] Table 2 Model parameters b k1 ~b k5 Value

[0049]

[0050] Table 3 Model parameters d s1 ~d s5 Value

[0051]

[0052]

[0053] In the embodiment of the present invention, the specific values ​​of each model parameter are obtained by finite element analysis. Figure 2 Shown is the finite element model of the disc specimen established by obtaining the model parameters.

[0054] S3. Perform multiple fatigue tests on the disc specimen at different displacement amplitudes to obtain the load-displacement hysteresis curve as well as displacement amplitude, load amplitude and life data.

[0055] like Figure 3 As shown, it is a schematic diagram of the configuration of a disc sample involved in an embodiment of the present invention, wherein the middle circular hole allows a loading mechanism to pass through the sample to perform fatigue loading on the sample.

[0056] like Figure 4 As shown, in the embodiment of the present invention, the fatigue testing mechanism is composed of upper and lower punches, upper and lower clamps and a central circular hole specimen. The upper and lower clamps can fix the specimen, and then connect the upper and lower punches through the central circular hole to complete the fatigue loading of the disc specimen.

[0057] S4. Perform power law fitting on the load-displacement hysteresis curve to obtain the Hollomon law parameters of the material of the disc specimen.

[0058] In the embodiment of the present invention, the iterative solution formula of the Hollomon law parameter of the material is:

[0059]

[0060] Where n and K are the Hollomon law parameters of the material, m represents the loading coefficient obtained by power law fitting of the load-displacement hysteresis curve, and C represents the loading index obtained by power law fitting of the load-displacement hysteresis curve.

[0061] S5. According to the correlation equation, the displacement amplitude and load amplitude are converted into the corresponding strain amplitude and stress amplitude.

[0062] S6. Determine the Manson-Coffin law parameters of the material of the disc specimen based on the strain amplitude and life data.

[0063] In the embodiment of the present invention, the formula of the material Manson-Coffin law parameter in step S6 is:

[0064]

[0065] Where E represents the elastic modulus of the material, N f represents the life data, σ f ′、ε f ′, β and γ are all material Manson-Coffin law parameters.

[0066] like Figure 5 As shown, under different material performance parameters, the material stress-strain curve preset by the finite element method is closely consistent with the model prediction result of the embodiment of the present invention, which proves that the material stress-strain curve predicted by the method of the present invention has high accuracy.

[0067] Figure 6 The material fatigue life obtained by the method of the present invention is compared with the traditional test results, and the two are in good agreement. Therefore, the method of the present invention is suitable for simultaneously obtaining the uniaxial stress-strain relationship and fatigue performance of service structural materials (or small-sized mechanical components and small-sized new materials).

[0068] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A micro-sample testing method for obtaining material fatigue properties based on disc specimens, It is characterized in that The following steps are involved: S1. Construct the equivalent stress and equivalent strain equations at the midpoint of the disc specimen; S2. Construct the correlation equation between the stress amplitude and strain amplitude of the disc specimen under fatigue test and the equivalent stress and equivalent strain of the midpoint; S3, performing multiple fatigue tests on the disc specimen at different displacement amplitudes to obtain load-displacement hysteresis curves as well as displacement amplitude, load amplitude and life data; S4, performing power law fitting on the load-displacement hysteresis curve to obtain the Hollomon law parameters of the material of the disc sample; S5. According to the correlation equation, the displacement amplitude and the load amplitude are converted into the corresponding strain amplitude and stress amplitude; S6. Determine the Manson-Coffin law parameters of the material of the disc specimen based on the strain amplitude and life data.

2. The micro-sample testing method for obtaining material fatigue properties based on a disc specimen according to claim 1, It is characterized in that The equivalent stress and equivalent strain equations of the midpoint of the disc sample in step S1 are specifically: where σ eq-C represents the equivalent stress at the midpoint, P represents the load, h represents the displacement, ε eq-C represents the equivalent strain at the midpoint, A * represents the characteristic area, h * represents the characteristic displacement, k 1 , k 2 , k 3 and k 4 are the model parameters of the equivalent stress and equivalent strain equation model at the midpoint of the disc specimen, k 5 and k 6 They are all intermediate parameters, and n represents the Hollomon law parameter of the material.

3. The micro-sample testing method for obtaining material fatigue properties based on a disc sample according to claim 2, It is characterized in that The correlation equation in step S2 is specifically: where σ a represents the stress amplitude, ε a represents the strain amplitude, e represents the natural constant, a 1 、a 2 、a 3 、c 1 and c 4 are model parameters of the association equation model.

4. The micro-sample testing method for obtaining material fatigue properties based on a disc specimen according to claim 2, It is characterized in that The iterative solution formula of the material Hollomon's law parameter in step S4 is: Where n and K are the Hollomon law parameters of the material, m represents the loading coefficient obtained by power law fitting of the load-displacement hysteresis curve, and C represents the loading index obtained by power law fitting of the load-displacement hysteresis curve.

5. The micro-sample testing method for obtaining material fatigue properties based on a disc specimen according to claim 3, It is characterized in that The formula of the material Manson-Coffin law parameter in step S6 is: Where E represents the elastic modulus of the material, N f represents the life data, σ f ′、ε f ′, β and γ are all material Manson-Coffin law parameters.

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