Method and system for evaluating true stress of multi-mode coupled metal structural member

Abstract

The invention discloses a method and a system for evaluating true stress of a multi-modal coupled metal structural member, and relates to the technical field of vehicle testing, the method comprises the following steps: carrying out multi-modal testing on the metal structural member by adopting a multi-modal mechanical testing system to obtain intrinsic parameters of the metal structural member, including yield strength, tensile strength and elongation at break; calculating a strength coefficient and a strain hardening index of the metal structural member according to the yield strength, the tensile strength and the elongation at break of the metal structural member, and solving the strength coefficient and the strain hardening index by adopting a hybrid optimization algorithm; acquiring a strain test value of a strain test on the metal structural member through the strain gauge; and calculating the real stress of the metal structural member according to the elastic modulus, the strength coefficient, the strain hardening index and the strain test value in the intrinsic parameters of the metal structural member. According to the invention, the problem of inaccurate test caused by distortion in stress test of the metal structural member in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle testing, and particularly relates to a method and system for evaluating the true stress of a metal structural member with multimodal coupling. Background Art

[0002] Generally, in order to obtain the true stress of a certain dangerous part of a structure, a unidirectional strain gauge (or strain rosette) is pasted at that position, and the strain gauge will record the strain history in the time domain.

[0003] The existing engineering method calculates the stress of the structure through the elastic relationship Hooke's theorem: stress = material elastic modulus * strain. This method has drawbacks because there is a general microscopic yield phenomenon in metal materials, and using Hooke's theorem of elastic relationship will result in distortion, and the obtained stress will be larger than the true stress, leading to inaccurate testing. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method and system for evaluating the true stress of a metal structural member with multimodal coupling, aiming to solve the problem of distortion in stress testing of metal structural members in the existing technology, resulting in inaccurate testing.

[0005] The first aspect of the present invention provides a method for evaluating the true stress of a metal structural member with multimodal coupling, and the method includes:

[0006] Performing multimodal testing on the metal structural member by using a multimodal mechanical testing system to obtain the intrinsic parameters of the metal structural member, including yield strength, tensile strength, and fracture elongation;

[0007] According to the yield strength, tensile strength, and fracture elongation of the metal structural member, calculating the strength coefficient and strain hardening index of the metal structural member, and using a hybrid optimization algorithm to solve the strength coefficient and the strain hardening index;

[0008] Obtaining the strain test value of the strain test on the metal structural member through the strain gauge;

[0009] Calculating the true stress of the metal structural member according to the elastic modulus in the intrinsic parameters of the metal structural member, and the strength coefficient, the strain hardening index, and the strain test value.

[0010] According to one aspect of the above technical solution, the step of calculating the strength coefficient and strain hardening index of the metal structural member according to the yield strength, tensile strength, and fracture elongation of the metal structural member, and using a hybrid optimization algorithm to solve the strength coefficient and the strain hardening index includes:

[0011] Couple the Ramberg-Osgood model with the modified Voce hardening model to construct a dual-mechanism hardening equation:

[0012]

[0013] In the formula, ε is the total strain, σ is the true stress, E is the elastic modulus, K is the strength coefficient, n is the strain hardening index, and θ and β are both dislocation density evolution parameters;

[0014] Combine the residual stress field distribution measured by X-ray diffraction and the EBSD orientation imaging data to construct a microscopic hardening constraint function:

[0015] H = f(ρ dislocation , Δd / d 0 );

[0016] In the formula, ρ dislocation is the dislocation density calibrated by TEM of the transmission electron microscope, and Δd / d 0 is the lattice constant change rate;

[0017] Use a hybrid optimization algorithm to correct the macroscopic parameter solution obtained from the dual-mechanism hardening equation.

[0018] According to one aspect of the above technical solution, the steps of obtaining the strain test value of the strain test on the metal structural member through the strain gauge include:

[0019] Paste a strain gauge on the surface of the metal structural member and establish an electrical connection between the strain gauge and the multi-modal mechanical testing system;

[0020] Apply a horizontal tensile force to the metal structural member along the length direction of the metal structural member to cause a resistance change in the strain gauge, and determine the strain test value of the metal structural member through the resistance change of the strain gauge.

[0021] According to one aspect of the above technical solution, the steps of obtaining the strain test value of the strain test on the metal structural member through the strain gauge include:

[0022] Apply a horizontal tensile force to the metal structural member along the length direction of the metal structural member;

[0023] Paste a strain gauge on the surface of the metal structural member and establish an electrical connection between the strain gauge and the multi-modal mechanical testing system;

[0024] When the metal structural member yields, the strain gauge generates a resistance change, and the strain test value of the metal structural member is determined through the resistance change of the strain gauge.

[0025] According to one aspect of the above technical solution, after the step of calculating the true stress of the metal structural member according to the elastic modulus in the intrinsic parameters of the metal structural member, and the strength coefficient, the strain hardening index and the strain test value, the method further includes:

[0026] Performing micron-level CT scanning on the metal structural member by a radiation light source to reconstruct a three-dimensional true strain field;

[0027] Comparing the three-dimensional true strain field with the calculation result of the true stress voxel by voxel to calculate the Pearson correlation coefficient;

[0028] When the Pearson correlation coefficient is greater than a preset value, it is determined that the evaluation result of the true stress of the metal structural member is valid.

[0029] According to one aspect of the above technical solution, the preset value of the Pearson correlation coefficient is 0.95.

[0030] The second aspect of the present invention is to provide a multi-modal coupled true stress evaluation system for metal structural members, and the system is applied to the method described in the above technical solution.

[0031] Compared with the prior art, the beneficial effects of adopting the multi-modal coupled true stress evaluation method and system for metal structural members shown in the present invention are as follows:

[0032] The present invention performs multi-modal tests on metal structural members by using a multi-modal mechanical test system to obtain the intrinsic parameters of the metal structural members, including yield strength, tensile strength and elongation at break; calculates the strength coefficient and strain hardening index of the metal structural members according to the yield strength, tensile strength and elongation at break of the metal structural members, and uses a hybrid optimization algorithm to solve the strength coefficient and strain hardening index; obtains the strain test value of the strain test on the metal structural member by a strain gauge; calculates the true stress of the metal structural member according to the elastic modulus in the intrinsic parameters of the metal structural member, and the strength coefficient, strain hardening index and strain test value. Then, the present invention performs multi-modal tests on metal structural members by using a multi-modal mechanical test system to realize the full-dimensional calibration of material intrinsic parameters, avoid parameter errors caused by a single test mode, and at the same time combine a hybrid optimization algorithm and microstructure constraints to significantly improve the inversion accuracy of the strength coefficient and hardening index, and solve the problem of insufficient adaptability of the traditional Ramberg-Osgood model to the hardening behavior of complex materials. Description of the Drawings

[0033] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0034] Figure 1Schematic flow diagram of a method for evaluating the true stress of a multimodal-coupled metal structural member in an embodiment of the present invention. Detailed implementation manners

[0035] To make the objectives, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description of the specific implementation manners of the present invention with reference to the accompanying drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used herein in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0037] Embodiment 1

[0038] Please refer to Figure 1 , the first embodiment of the present invention provides a method for evaluating the true stress of a multimodal-coupled metal structural member, and the method includes steps S10 - step S40:

[0039] Step S10, perform multimodal testing on the metal structural member using a multimodal mechanics testing system to obtain the intrinsic parameters of the metal structural member, including yield strength, tensile strength, and fracture elongation.

[0040] First, it should be noted that the metal structural member to be tested and evaluated in this embodiment is a component in an automobile, such as a cross beam, longitudinal beam, reinforcement beam, etc. metal structural member, which requires good performance. Therefore, in this embodiment, a method for evaluating the true stress of a multimodal-coupled metal structural member is used to test and evaluate the metal structural member.

[0041] Specifically, in this embodiment, multimodal testing will first be performed on the metal structural member through a multimodal mechanics testing system. The multimodal mechanics testing system such as quasi-static-dynamic coupled loading, DIC full-field strain analysis, temperature-strain rate synchronous control is used to obtain the intrinsic parameters of the metal structural member. The intrinsic parameters include the yield strength, tensile strength, and fracture elongation of the metal structural member.

[0042] Step S20, calculate the strength coefficient and strain hardening index of the metal structural member according to the yield strength, tensile strength, and fracture elongation of the metal structural member, and use a hybrid optimization algorithm to solve the strength coefficient and the strain hardening index.

[0043] In this embodiment, according to the yield strength, tensile strength and fracture elongation rate of the metal structural member, calculating the strength coefficient and strain hardening index of the metal structural member, and the steps of solving the strength coefficient and the strain hardening index by using a hybrid optimization algorithm include:

[0044] Couple the Ramberg-Osgood model and the modified Voce hardening model to construct a two-mechanism hardening equation:

[0045]

[0046] In the formula, ε is the total strain, σ is the true stress, E is the elastic modulus, K is the strength coefficient (stress dimension), n is the strain hardening index (dimensionless), and θ and β are both dislocation density evolution parameters;

[0047] Combined with the residual stress field distribution measured by X-ray diffraction and the EBSD orientation imaging data, construct a microscopic hardening constraint function:

[0048] H = f(ρ dislocation , Δd / d 0 );

[0049] In the formula, ρ dislocation is the dislocation density calibrated by TEM of the transmission electron microscope, and Δd / d 0 is the lattice constant change rate;

[0050] Use a hybrid optimization algorithm to correct the macroscopic parameter solution obtained by the two-mechanism hardening equation.

[0051] Among them, the hybrid optimization algorithm is a hybrid algorithm of genetic algorithm + particle swarm optimization.

[0052] Step S30, obtaining the strain test value of the strain test of the metal structural member through a strain gauge.

[0053] In this embodiment, the steps of obtaining the strain test value of the strain test of the metal structural member through a strain gauge include:

[0054] Paste a strain gauge on the surface of the metal structural member and establish an electrical connection between the strain gauge and the multi-modal mechanical testing system;

[0055] Apply a horizontal tensile force to the metal structural member along the length direction of the metal structural member, so that the resistance value of the strain gauge changes, and determine the strain test value of the metal structural member through the resistance value change of the strain gauge.

[0056] Step S40, calculating the true stress of the metal structural member according to the elastic modulus in the intrinsic parameters of the metal structural member, and the strength coefficient, the strain hardening index and the strain test value.

[0057] As a specific example, a metal structural member to be tested with dimensions of 10mm * 10mm * 100mm has an original length L = 100mm. The material of the structural body is aluminum alloy ADC12, with an elastic modulus = 71GPa, a Poisson's ratio = 0.33, and a density = 2.7E - 09 ton / mm^3. Through multi - modal testing of this metal structural member, the yield strength = 130MPa, the tensile strength = 230MPa, and the fracture elongation = 2%.

[0058] In the traditional method, it is assumed that a strain gauge is pre - pasted at the middle position of the metal structural member. The elongation direction of the strain gauge is parallel to the length direction of the metal structural member, and a deformation of DL = 1mm is applied in the length direction. At this time, the strain test value of the strain gauge = DL / L = 1mm / 100mm = 0.01. If the elastic relationship Hooke's theorem is used to obtain the maximum stress of the metal structural member = elastic modulus * strain = 71000MPa * 0.01 = 710MPa, which is much greater than the tensile strength of the metal structural member, 230MPa, resulting in the structural stress being much larger than the actual value. This is because only the elastic stage of the structure is considered, and the material plasticity is not considered.

[0059] In this embodiment, by obtaining the strength coefficient and strain hardening index of the metal structural member, with the material yield strength = 130MPa, the tensile strength = 230MPa, and the fracture elongation = 2%, and then establishing two simultaneous equations: the stress is 130MPa when the plastic strain is 0.2%, and the stress is 230MPa when the plastic strain is 2%. Then, according to the two - mechanism hardening equation, a hybrid optimization algorithm is used to obtain the strength coefficient = 606.3261MPa and the strain hardening index = 0.247784.

[0060] Given that the strain of the metal structural member in the length direction is 1%, and the elastic modulus, strength coefficient, and strain hardening index are all known values. According to the two - mechanism hardening equation, the true stress of the structure can be obtained as 180MPa, which is much smaller than the 710MPa calculated by only considering the elastic stage of the structure without considering material plasticity.

[0061] Compared with the prior art, the beneficial effect of adopting the method for evaluating the true stress of a metal structural member with multi - modal coupling shown in this embodiment is that:

[0062] The present invention performs multi-modal testing on metal structural components using a multi-modal mechanical testing system to obtain the intrinsic parameters of the metal structural components, including yield strength, tensile strength, and fracture elongation; calculates the strength coefficient and strain hardening index of the metal structural components based on the yield strength, tensile strength, and fracture elongation of the metal structural components, and uses a hybrid optimization algorithm to solve for the strength coefficient and strain hardening index; obtains the strain test values from the strain test on the metal structural components using strain gauges; calculates the true stress of the metal structural components based on the elastic modulus in the intrinsic parameters of the metal structural components, as well as the strength coefficient, strain hardening index, and strain test values. Then, the present invention performs multi-modal testing on metal structural components through a multi-modal mechanical testing system, realizes the full-dimensional calibration of material intrinsic parameters, avoids parameter errors caused by a single testing mode, and at the same time combines a hybrid optimization algorithm and microstructural constraints to significantly improve the inversion accuracy of the strength coefficient and hardening index, and solves the problem of insufficient adaptability of the traditional Ramberg-Osgood model to the hardening behavior of complex materials.

[0063] Embodiment 2

[0064] The second embodiment of the present invention also provides a method for evaluating the true stress of a metal structural component with multi-modal coupling, which is basically similar to the method shown in the first embodiment, except that:

[0065] In this embodiment, after the step of calculating the true stress of the metal structural component based on the elastic modulus in the intrinsic parameters of the metal structural component, as well as the strength coefficient, the strain hardening index, and the strain test values, the method further includes:

[0066] Performing micron-level CT scanning on the metal structural component using a radiation light source to reconstruct a three-dimensional true strain field;

[0067] Comparing the three-dimensional true strain field with the calculation result of the true stress voxel by voxel to calculate the Pearson correlation coefficient;

[0068] When the Pearson correlation coefficient is greater than a preset value, it is determined that the evaluation result of the true stress of the metal structural component is valid.

[0069] Among them, the preset value of the Pearson correlation coefficient is 0.95.

[0070] Specifically, performing micron-level CT scanning on the metal structural component under a synchrotron radiation light source, reconstructing a three-dimensional true strain field in combination with digital volume correlation (DVC) technology, comparing it with the calculation result voxel by voxel, calculating the Pearson correlation coefficient Rp, and if the Pearson correlation coefficient Rp > 0.95, it is regarded as valid, and matching the calculated stress field with the AE event energy distribution in space and time. If it satisfies:

[0071]

[0072] In the formula, Const. is a constant related to the fracture toughness of the material, and the physical consistency of the verification stress evaluation is verified.

[0073] Example Three

[0074] The third embodiment of the present invention provides a true stress evaluation system for a multimodal-coupled metal structural member, and the system is applied to the method described in the above embodiments.

[0075] Compared with the prior art, the beneficial effects of adopting the true stress evaluation system for the multimodal-coupled metal structural member shown in this embodiment are as follows:

[0076] The present invention performs multimodal tests on a metal structural member by using a multimodal mechanical test system to obtain the intrinsic parameters of the metal structural member, including the yield strength, tensile strength, and fracture elongation; calculates the strength coefficient and strain hardening index of the metal structural member according to the yield strength, tensile strength, and fracture elongation of the metal structural member, and uses a hybrid optimization algorithm to solve the strength coefficient and strain hardening index; obtains the strain test value of the strain test on the metal structural member through a strain gauge; calculates the true stress of the metal structural member according to the elastic modulus in the intrinsic parameters of the metal structural member, as well as the strength coefficient, strain hardening index, and strain test value. Therefore, the present invention performs multimodal tests on a metal structural member by using a multimodal mechanical test system to achieve the full-dimensional calibration of the material intrinsic parameters, avoid parameter errors caused by a single test mode, and at the same time combine a hybrid optimization algorithm and microstructure constraints to significantly improve the inversion accuracy of the strength coefficient and hardening index, and solve the problem of insufficient adaptability of the traditional Ramberg-Osgood model to the hardening behavior of complex materials.

[0077] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0078] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A multi-modal coupled true stress assessment method for metal structures, characterized in that: The method comprises: Using a multi-modal mechanical testing system to perform multi-modal testing on metal structural parts to obtain intrinsic parameters of the metal structural parts, including yield strength, tensile strength and elongation at break; Calculating the strength coefficient and strain hardening exponent of the metal structural part according to the yield strength, tensile strength and elongation at break of the metal structural part, and solving the strength coefficient and the strain hardening exponent by using a hybrid optimization algorithm; Obtaining a strain test value of a strain test performed on the metal structural component through a strain gauge; The true stress of the metal structure is calculated according to the elastic modulus in the intrinsic parameters of the metal structure, the strength coefficient, the strain hardening exponent and the strain test value.

2. The multi-modal coupled metal structural component true stress assessment method according to claim 1, characterized in that: The steps of calculating the strength coefficient and strain hardening exponent of the metal structural part according to the yield strength, tensile strength and elongation at break of the metal structural part, and solving the strength coefficient and the strain hardening exponent by using a hybrid optimization algorithm include: The Ramberg-Osgood model is coupled with the modified Voce hardening model to construct a dual-mechanism hardening equation: Where ε is the total strain, σ is the true stress, E is the elastic modulus, K is the strength coefficient, n is the strain hardening exponent, and θ and β are dislocation density evolution parameters; Combining the residual stress field distribution measured by X-ray diffraction with the EBSD orientation imaging data, a micro-hardening constraint function is constructed: H=f(ρ dislocation , Δd / d0); In the formula, ρ dislocation is the dislocation density calibrated by transmission electron microscope TEM, Δd / d0 is the rate of change of lattice constant; A hybrid optimization algorithm is used to correct the macroscopic parameter solution obtained by the dual-mechanism hardening equation.

3. The multi-modal coupled metal structural component true stress assessment method according to claim 1, characterized in that: The step of obtaining a strain test value of a strain test performed on the metal structural member by means of a strain gauge comprises: Pasting a strain gauge on the surface of the metal structure, and establishing an electrical connection between the strain gauge and the multi-modal mechanical testing system; A horizontal tensile force is applied to the metal structural member along the length direction of the metal structural member to cause the resistance value of the strain gauge to change, and the strain test value of the metal structural member is determined by the resistance value change of the strain gauge.

4. The multi-modal coupled metal structural component true stress assessment method according to claim 1, characterized in that: The step of obtaining a strain test value of a strain test performed on the metal structural member by means of a strain gauge comprises: Applying a horizontal tensile force to the metal structure along the length direction of the metal structure; Pasting a strain gauge on the surface of the metal structure, and establishing an electrical connection between the strain gauge and the multi-modal mechanical testing system; When the metal structural component yields, the strain gauge generates a resistance change, and the strain test value of the metal structural component is determined by the resistance change of the strain gauge.

5. The multi-modal coupled metal structural component true stress assessment method according to claim 1, characterized in that: After the step of calculating the true stress of the metal structure according to the elastic modulus in the intrinsic parameters of the metal structure, the strength coefficient, the strain hardening exponent and the strain test value, the method further includes: Performing micrometer-level CT scanning on the metal structural component by using a radiation light source to reconstruct a three-dimensional real strain field; Comparing the calculated results of the three-dimensional true strain field and the true stress voxel by voxel, and calculating the Pearson correlation coefficient; When the Pearson correlation coefficient is greater than a preset value, it is determined that the true stress evaluation result of the metal structural component is valid.

6. The multi-modal coupled metal structural component true stress assessment method according to claim 5, characterized in that: The preset value of the Pearson correlation coefficient is 0.

95.

7. A multi-modal coupled metal structural component real stress assessment system, characterized in that: The system is applied to the method described in any one of claims 1-6.

Images