A method and device for obtaining a solder material sn curve

Abstract

The application discloses a kind of weld point material SN curve acquisition method and device, it is related to material data analysis field, including the following steps: setting load test condition, the fatigue limit load of test material is determined, the relationship between the weld point force-test cycle number of test material is obtained;The strain gauge patch position near weld point is calculated, to calculate the strain at weld point;According to the fatigue limit load obtained by measurement, load consistent with the direction of unit force in simulation model, the strain at strain patch is calculated;The weld point simulation model is corrected and loaded with the unit force consistent with the direction of load test, output weld point unit force, further obtain weld point unit stress;Based on weld point unit force and weld point unit stress, the unit force-stress relationship of weld point is obtained, and the SN curve of weld point material is obtained by combining weld point force-test cycle number relationship.The application improves the accuracy of weld point durability analysis, is suitable for conventional metal, with universality.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material data analysis, in particular to a method and device for obtaining a SN curve of a welding point material. BACKGROUND

[0002] Welding points are crucial to the service life and safety of a vehicle, so it is necessary to conduct a welding point durability analysis on the vehicle; in the prior art, a welding point durability analysis is directly performed by using a welding point material SN curve (stress-life curve) provided in a material database, or by selecting a load-life curve of a suitable point welding type according to the method of the existing standard BS7608. However, the number of welding point material SN curves in the existing database is small, while the types of welding point materials are numerous, and the welding point material SN curves in the existing database cannot be applied to all types of welding point materials, and are not universal, and the calculation accuracy is low; and the method of the existing standard BS7608 is directed to different welding point types, rather than different materials, resulting in low calculation accuracy. SUMMARY

[0003] In view of the defects in the prior art, the purpose of the present application is to provide a method and device for obtaining a SN curve of a welding point material. The SN curve of the welding point material of different welding point materials can be obtained, so that an accurate welding point durability analysis can be performed on the welding point, the accuracy of the welding point durability analysis is improved, and the method is applicable to conventional metals and is universal.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] The load test conditions are set, and the fatigue limit load of the test material is determined based on the step method to obtain the relationship between the welding point force and the test cycle number of the test material;

[0006] The welding point test is simulated, and the strain gauge patch positions of a plurality of points near the welding point are calculated to calculate the strain at the welding point;

[0007] According to the determined fatigue limit load, a unit force consistent with the direction of the load test is loaded in the simulation model to calculate the strain at the strain patch near the welding point;

[0008] According to the calculated strain at the welding point and the strain at the strain patch near the welding point, the welding point simulation model is corrected, and a unit force consistent with the direction of the load test is loaded on the welding point simulation model to output the welding point unit force, and the welding point unit stress is obtained based on the output welding point unit force;

[0009] Based on the welding point unit force and the welding point unit stress, the unit force-stress relationship of the welding point is obtained, and the SN curve of the welding point material is obtained in combination with the welding point force-test cycle number relationship.

[0010] On the basis of the above technical solutions, before the test condition is set, the ultimate load of the test material is determined based on the step method, and the relationship between the welding point force and the test cycle number of the test material is obtained, further comprising:

[0011] The type and thickness of the test material are determined, the sample size, clamp and welding point diameter are determined according to the testing machine, the number of test materials and the cycle base are selected, and the stress ratio is set for use in the welding point test process.

[0012] On the basis of the above technical solutions, the ultimate load of the test material is determined based on the step method, and the specific steps include:

[0013] The load level and load increment of the test material are set, and the following steps are cycled:

[0014] The ultimate load test is performed on the current test material based on the load level and cycle base, and according to the ultimate load test result:

[0015] If the ultimate load test result of the current test material is failure, the load level of the next test material ultimate load test is reduced by one based on the load increment;

[0016] If the ultimate load test result of the current test material is exceeded, the load level of the next test material ultimate load test is increased by one based on the load increment;

[0017] If the ultimate load test result of the current test material is base metal non-heat affected zone fracture, the current test data is invalid.

[0018] On the basis of the above technical solutions, the strain gauge patch position should meet the distance from the welding point within the range of the heat affected zone, and the distance from the welding point should not be less than a preset multiple of the strain gauge width.

[0019] On the basis of the above technical solutions, after the strain gauge patch positions of a preset number of points near the welding point are calculated to calculate the strain at the welding point, further comprising:

[0020] Based on the calculated strain gauge patch positions, the test strain-time history data of the strain gauge along the load test tensile direction is collected during the welding point test process.

[0021] On the basis of the above technical solutions, the strain at the strain patch near the welding point is calculated by loading a unit force consistent with the load test direction in the simulation model, and the specific steps include:

[0022] A unit force consistent with the load test direction is loaded in the simulation model, and the welding point unit force is output;

[0023] In the fatigue calculation software, the weld point unit force is superimposed on the test load spectrum, and the stress at the strain patch position is output;

[0024] The stress at the output strain patch is converted into the strain at the strain patch.

[0025] On the basis of the above technical solutions, the weld point unit stress is obtained based on the output weld point unit force, and the specific steps include:

[0026] In the fatigue calculation software, the weld point unit force is superimposed on the test load spectrum, and the stress at the strain patch position is output;

[0027] On the basis of the above technical solutions, the weld point simulation model is corrected, and the specific steps include:

[0028] The calculated strain at the weld point is compared with the strain at the strain patch near the weld point, and the weld point finite element model is corrected to ensure that the strain at the weld point and the strain at the strain patch near the weld point are consistent to more than a preset value.

[0029] The present application also provides a kind of weld point material SN curve acquisition device, including:

[0030] The determination module is used to determine the fatigue limit load of the test material based on the ladder method according to the set load test condition, and obtain the relationship between the weld point force and the test cycle number of the test material;

[0031] The calculation module is used to calculate the strain patch position of a plurality of points near the weld point by simulating the weld point test, to calculate the strain at the weld point; and according to the fatigue limit load determined by the determination module, a unit force consistent with the load test direction is loaded in the simulation model, and the strain at the strain patch near the weld point is calculated;

[0032] The execution module is used to correct the weld point simulation model based on the strain at the weld point and the strain at the strain patch calculated by the calculation module, load the unit force consistent with the load test direction, output the weld point unit force, and obtain the weld point unit stress based on the output weld point unit force; based on the weld point unit force and the weld point unit stress, the weld point unit force-stress relationship is obtained, and the weld point material SN curve is obtained by combining the weld point-cycle number relationship.

[0033] On the basis of the above technical solutions, before the limit load of the test material is determined based on the ladder method according to the set load test condition, and the relationship between the weld point force and the test cycle number of the test material is obtained, it further includes:

[0034] Determine the type and thickness of the test material, determine the sample size, clamp and weld point diameter according to the testing machine, select the number of test materials and the cycle base, and set the stress ratio for use in determining the fatigue limit load of the test material.

[0035] Compared with the prior art, the advantages of the present application are that the welding point material SN curve acquisition method and device can obtain the welding point material SN curves of different welding point materials, thereby accurately analyzing the welding point durability, improving the accuracy of the welding point durability analysis, and avoiding the problem of low calculation accuracy of the force-life curve by obtaining the welding point stress-life relationship curve according to the force-stress and force-life relationship; the calculated strain at the strain patch position is marked with the test strain to correct the welding point finite element model, thereby improving the calculation accuracy; the present application is suitable for conventional metals and has universality. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0037] Figure 1 The flowchart of the welding point material SN curve acquisition method in the embodiment of the present application is shown in the figure.

[0038] Figure 2 The material welding schematic diagram of the welding point material SN curve acquisition method in the embodiment of the present application is shown in the figure.

[0039] Figure 3 The strain patch position schematic diagram of the welding point material SN curve acquisition method in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments.

[0041] Referring to Figure 1 The welding point material SN curve acquisition method provided by the embodiment of the present application includes the following steps:

[0042] S1: Set the load test conditions and determine the fatigue limit load of the test material based on the step method to obtain the relationship between the welding point force and the test cycle number of the test material.

[0043] S2: simulate the solder test through simulation, and calculate the strain gauge patch positions of multiple points near the solder to calculate the strain at the solder;

[0044] S3: according to the measured fatigue limit load, load a unit force consistent with the load test direction in the simulation model, and calculate the strain at the strain gauge patch near the solder;

[0045] S4: according to the calculated strain at the solder and the strain at the strain gauge patch near the solder, correct the solder simulation model, load a unit force consistent with the load test direction on the solder simulation model, output the solder element force, and obtain the solder element stress based on the output solder element force.

[0046] S5: based on the solder element force and the solder element stress, obtain the element force-stress relationship of the solder, and combine the solder force-test cycle number relationship to obtain the SN curve of the solder material.

[0047] That is, first set the load test conditions, determine the conditional fatigue limit load by using the step method, the load level of the first test material sample should be selected to be slightly higher than the expected fatigue limit, and the test is generally carried out at 3-5 levels of equal-interval load levels. The selected load increment should be close to the standard deviation of the sub-sample, if it is difficult to estimate the standard deviation of the sub-sample, about 3%-5% of the estimated fatigue strength can be selected, the load level of the next sample is determined (reduced or increased) according to the test result (failure or exceeded) of the last sample, when the test accuracy reaches the required accuracy, the fatigue limit load of the test material is obtained. During the test process, a force is loaded on the test material based on the set load level and cycled for a predetermined number of times, and the relationship between the solder force and the test cycle number can be obtained after the test is completed.

[0048] Then determine the position of the strain gauge patch. The strain at the solder has singularity and cannot be directly tested, the strain gauge patch positions of 2-3 points near the solder are calculated and obtained through simulation of the solder test scheme, and the strain gauge patch should be arranged at least 2 to inversely deduce the strain at the solder, that is, the simulation strain, but due to the size limitation of the test sample, the strain gauge patch should not be too much.

[0049] Based on the fatigue limit load, a unit force consistent with the limit load test direction is loaded in the simulation model, and the strain at the strain gauge patch position near the solder is calculated, that is, the test strain.

[0050] According to the calculated simulation strain and test strain, the solder simulation model is corrected, a unit force consistent with the limit load test direction is loaded on the corrected simulation model, and the solder element force is output, and the solder element stress is obtained based on the output solder element force.

[0051] Based on the obtained solder joint unit force and solder joint unit stress, a solder joint unit force-stress relationship is obtained, and then a solder joint material stress-life relationship curve, i.e., a SN curve of the solder joint material, is obtained according to a solder joint force-test cycle number relationship. Alternatively, according to the stress at the test patch position, a structural stress method is applied to derive the stress at the solder toe, from which a force-stress relationship is obtained, so that the solder joint material stress-life curve is calculated.

[0052] In the present application, before setting the test conditions and obtaining the relationship between the solder joint force and the test cycle number of the test material based on the step-by-step method, the following steps are further included:

[0053] The type and thickness of the test material are determined, the sample size, the clamp, and the solder joint diameter are determined according to the testing machine, the number of test materials and the cycle base are selected, and the stress ratio is set for use in the solder joint test.

[0054] That is, before setting the test conditions and obtaining the relationship between the solder joint force and the test cycle number of the test material based on the step-by-step method, the type and thickness of the test material selected by the test material are determined, the sample size, the clamp, and the solder joint diameter are determined according to the testing machine, and the appropriate number of test materials and the cycle base are selected, and the stress ratio is determined.

[0055] In the present application, the specific steps for determining the ultimate load of the test material based on the step-by-step method include:

[0056] The load level and the load increment of the test material are set, and the following steps are cycled:

[0057] The ultimate load test is performed on the current test material based on the load level and the cycle base, and according to the ultimate load test results:

[0058] If the ultimate load test result of the current test material is failure, the load level of the next test material ultimate load test is reduced by one level based on the load increment;

[0059] If the ultimate load test result of the current test material is exceedance, the load level of the next test material ultimate load test is increased by one level based on the load increment;

[0060] If the ultimate load test result of the current test material is base metal non-heat affected zone fracture, the current test data is invalid.

[0061] The specific steps of determining the limit load of the test material based on the step method are as follows: the load level and the load increment of the test material are set first, the load level of the first sample should be selected to be slightly higher than the expected fatigue limit, and the test is generally carried out at 3-5 load levels with equal intervals. The selected load increment should be close to the standard deviation of the sub-sample, if it is difficult to estimate the standard deviation of the sub-sample, about 3%-5% of the estimated fatigue strength can be selected, and then the following steps are repeated until the test result accuracy reaches the required accuracy:

[0062] Based on the selected load level and the cycle base, the fatigue limit load test of the current test material is carried out, if the limit load test result of the previous test material is failure, the load level of the limit load test of the next test material is reduced by one level based on the load increment; if the limit load test result of the current test material is exceed, the load level of the limit load test of the next test material is increased by one level based on the load increment; if the limit load test result of the current test material is the fracture of the base material non-heat affected zone, the current test data is invalid.

[0063] Wherein, the test result for failure is that the test material appears cracks and does not break, and the test result for exceed is that the test material does not appear damage.

[0064] In the application, the strain patch position should meet the following conditions: the distance from the welding point is within the range of the heat affected zone, and the distance from the welding point is not less than the strain patch width of the preset multiple.

[0065] That is, the strain patch position should meet the following conditions: the distance from the welding point can show the high stress influence of the heat affected zone and will not be too high to cause stress singularity, that is, within the range of the heat affected zone, but the distance from the welding point should be at least 1.5-2.5 times the strain patch width.

[0066] In the application, after the strain patch positions of the preset number of points near the welding point are calculated to calculate the strain at the welding point, the following steps are further included:

[0067] Based on the calculated strain patch positions, the test strain-time history data of the strain patch along the tensile direction of the load test are collected during the welding point test.

[0068] That is, based on the calculated strain patch along the tensile direction of the load test, the test strain-time history data are collected during the welding point test.

[0069] In the application, the strain at the strain patch near the welding point is calculated by loading a unit force consistent with the load test direction in the simulation model, and the specific steps include:

[0070] A unit force consistent with the load test direction is loaded in the simulation model, and the welding point unit force is outputted;

[0071] In the fatigue calculation software, the weld point unit force is superimposed on the test load spectrum, and the stress at the strain patch position is output;

[0072] The stress at the output strain patch is converted into the strain at the strain patch.

[0073] That is, a unit force consistent with the load test direction is loaded in the simulation model, and the strain at the strain patch near the weld point is calculated. The specific steps are as follows: first, a unit force consistent with the load test direction is loaded in the simulation model, and the weld point unit force is output; then, in the fatigue calculation software, the output weld point unit force is superimposed on the test load spectrum, and the stress at the strain patch position is output; and the output stress at the strain patch is converted into the strain at the strain patch.

[0074] In the present application, the weld point unit stress is obtained based on the output weld point unit force, and the specific steps include:

[0075] In the fatigue calculation software, the output weld point unit force is superimposed on the forces at each level of the weld point test to obtain the weld point unit stress.

[0076] That is, the weld point unit stress is obtained based on the output weld point unit force, and the specific steps are as follows: in the fatigue calculation software, the output weld point unit force is superimposed on the forces at each level of the weld point test to obtain the weld point unit stress, so that the weld point unit force-stress relationship can be obtained.

[0077] In the present application, the simulation model of the weld point is modified, and the specific steps include:

[0078] The calculated strain at the weld point is compared with the strain at the strain patch near the weld point, the finite element model of the weld point is modified, and the consistency of the strain at the weld point and the strain at the strain patch near the weld point is ensured to exceed a preset value.

[0079] That is, the simulation model of the weld point is modified, and the specific steps are as follows: the calculated strain at the weld point is compared with the strain at the strain patch near the weld point, that is, the simulation strain is compared with the test strain, the simulation model of the weld point is modified, and the consistency of the simulation strain and the test strain is ensured to exceed 80%. Or, the stress at the weld toe derived by the structural stress method is compared with the simulation weld point stress, and the model is modified.

[0080] In one possible implementation, the embodiment of the present application also provides a readable storage medium, which is located in a PLC (Programmable Logic Controller, Programmable Logic Controller) controller, and a computer program is stored on the readable storage medium. The program is executed by the processor to implement the steps of the following weld point material SN curve acquisition method:

[0081] The load test condition is set, and the fatigue limit load of the test material is determined based on the step method to obtain the relationship between the solder joint force and the test cycle number of the test material;

[0082] The solder joint test is simulated, and the strain gauge patch positions of multiple points near the solder joint are calculated to calculate the strain at the solder joint;

[0083] According to the determined fatigue limit load, a unit force consistent with the load test direction is loaded in the simulation model to calculate the strain at the strain gauge patch near the solder joint;

[0084] According to the calculated strain at the solder joint and the strain at the strain gauge patch near the solder joint, the solder joint simulation model is corrected, and a unit force consistent with the load test direction is loaded on the solder joint simulation model to output the solder joint element force, and the solder joint element stress is obtained based on the output solder joint element force;

[0085] Based on the solder joint element force and the solder joint element stress, the element force-stress relationship of the solder joint is obtained, and the SN curve of the solder joint material is obtained in combination with the solder joint force-test cycle number relationship.

[0086] The storage medium can adopt any combination of one or more computer-readable media. The computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may, for example, but is not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or apparatus, or any combination thereof. More specific examples (non-exhaustive list) of the computer-readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this document, the computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, device or apparatus.

[0087] Computer readable signal media can include a computer-readable instruction, data structures, program modules, or other data over a transmission medium, such as a carrier wave or other transport mechanism, and includes any information delivery or transport media. The aforementioned carrier wave, or other transport mechanism can take the form of electrical, electromagnetic, or optical, or any combination thereof, propagating data signals.

[0088] Computer program code for carrying out operations for aspects of the present application can be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like, and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0089] Embodiments of the present application also provide a solder joint material SN curve acquisition device, comprising:

[0090] The determination module is configured to determine the fatigue limit load of the test material based on the ladder method under the set load test condition, and obtain the relationship between the solder joint force and the test cycle number of the test material.

[0091] The calculation module is configured to calculate the strain gauge patch positions of the preset number of points near the solder joint by simulating the solder joint test, to calculate the strain at the solder joint; and load a unit force consistent with the load test direction in the simulation model according to the fatigue limit load determined by the determination module, to calculate the strain at the strain gauge patch near the solder joint.

[0092] The execution module is used for correcting the simulation model of the welding point based on the strain at the welding point and the strain at the strain patch calculated by the calculation module, loading a unit force consistent with the load test direction, outputting a welding point unit force, and obtaining a welding point unit stress based on the output welding point unit force; based on the welding point unit force and the welding point unit stress, a welding point unit force-stress relationship is obtained, and a welding point material SN curve is obtained in combination with a welding point-cycle number relationship.

[0093] That is, the embodiment of the present application also provides a welding point material SN curve acquisition device, which comprises a determination module, a calculation module and an execution module, the test module is used for determining the fatigue limit load of the test material based on the step method under the set load test condition, and obtaining the welding point force-test cycle number relationship of the test material; the calculation module is used for calculating the strain patch positions of a preset number of points near the welding point by simulating the welding point test, calculating the strain at the welding point, and loading a unit force consistent with the load test direction in the simulation model according to the fatigue limit load determined by the determination module, and calculating the strain at the strain patch near the welding point; the execution module is used for correcting the simulation model of the welding point based on the strain at the welding point and the strain at the strain patch calculated by the calculation module, loading a unit force consistent with the load test direction, outputting a welding point unit force, and obtaining a welding point unit stress based on the output welding point unit force; based on the welding point unit force and the welding point unit stress, a welding point unit force-stress relationship is obtained, and a welding point material SN curve is obtained in combination with a welding point-cycle number relationship.

[0094] In the present application, before the limit load of the test material is determined based on the step method under the set load test condition, the welding point force-test cycle number relationship of the test material is obtained, and the following steps are further included:

[0095] The type and thickness of the test material are determined, the sample size, clamp and welding point diameter are determined according to the testing machine, the number of test materials and the cycle base are selected, and the stress ratio is set, which is used in the process of determining the fatigue limit load of the test material.

[0096] That is, before the limit load of the test material is determined based on the step method under the set load test condition, the welding point force-test cycle number relationship of the test material is obtained, and the following steps are further included:

[0097] Embodiment one, welding point test scheme:

[0098] According to the historical cracking situation, the materials and thicknesses used at the positions where cracking is more are selected as the sample material and thickness of the welding point test;

[0099] Determine the specimen size, the specimen size selection must ensure that the test load within the allowable load range of the testing machine;

[0100] The specimen is welded according to the requirements, the welding spot should not be welded through the specimen, and there should be no false welding. The diameter of the welding spot should not be less than 4.25√δ (δ is the equivalent plate thickness, δ1 and δ2 are the thicknesses of the materials in the lap joint combination, the calculation method is δ = 0.8δ1 + 0.2δ2 (δ1 ≤ δ2), unit: mm). The welding spot test scheme is as follows Figure 2 ;

[0101] The number of specimens in each batch should not be less than 30, and the stress ratio R is generally taken as 0-0.2.

[0102] Example two, strain measurement:

[0103] A simulation model of the welding spot test is established, a unit force consistent with the test direction is loaded, and the force of the welding spot element is output;

[0104] The strain gauge patch positions of 2-3 points near the welding spot are obtained through simulation calculation. The positions should meet the following requirements: the distance from the welding spot should be able to show the high stress influence of the heat affected zone and not be too high to cause stress singularity, and the strain gauge position diagram is as follows Figure 3 .

[0105] Strain gauges along the tensile load direction are attached at the above positions to obtain the test strain-time history curve.

[0106] Example three, model correction:

[0107] In the fatigue calculation software, the force results of the welding spot element obtained through the above simulation are superimposed on the actual test load spectrum to obtain the simulation stress at the strain gauge patch position;

[0108] The simulation stress is converted into simulation strain;

[0109] The simulation strain is compared with the test strain, and the welding spot finite element model is corrected to ensure that the simulation strain and the test strain are consistent to more than 80%.

[0110] Example four, SN curve acquisition of welding spot material:

[0111] In the corrected model, a unit force consistent with the test direction is loaded, and the force of the welding spot element is output;

[0112] In the fatigue calculation software, the test forces of each level are superimposed to obtain the welding spot element stress;

[0113] According to the force-stress and force-life relationship, the welding spot stress-life relationship curve is obtained.

[0114] The foregoing detailed description of the application has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed, and various modifications and variations are possible in light of the above teachings or can be acquired from practice of the application. The

[0115] The computer program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of Figure 1 The flow diagram and / or block diagram in this disclosure can represent one or more of any appropriate circuitry configured to perform the specified functions. In this regard, each block in the flow diagram and / or block diagram can represent a module, segment, or portion of code which comprises one or more executable instructions for implementing the specified Figure 1 The flow diagram and / or block diagram in this disclosure can represent one or more of any appropriate circuitry configured to perform the specified functions. In this regard, each block in the flow diagram and / or block diagram can represent a module, segment, or portion of code which comprises one or more executable instructions for implementing the specified

Claims

1. A method for acquiring an SN curve of a solder joint material, characterized by, The method comprises the following steps: Setting a load test condition and determining a fatigue limit load of the test material based on a step-by-step method to obtain a relationship between a weld point force and a test cycle number of the test material; Simulating the weld point test and calculating strain gauge patch positions of multiple points near the weld point to calculate a strain at the weld point; Loading a unit force consistent with a load test direction in the simulation model according to the determined fatigue limit load to calculate a strain at the strain gauge patch positions near the weld point; According to the calculated strain at the weld point and the strain at the strain gauge patch positions near the weld point, the weld point simulation model is corrected, and a unit force consistent with the load test direction is loaded on the weld point simulation model to output a weld point unit force, and a weld point unit stress is obtained based on the output weld point unit force; Based on the weld point unit force and the weld point unit stress, a relationship between the weld point unit force and the weld point unit stress is obtained, and an SN curve of the weld point material is obtained in combination with the relationship between the weld point force and the test cycle number. The steps of correcting the weld point simulation model include: The calculated strain at the weld point and the strain at the strain gauge patch positions near the weld point are compared, and the weld point finite element model is corrected to ensure that the strain at the weld point and the strain at the strain gauge patch positions near the weld point are consistent to more than a preset value.

2. The method of claim 1, wherein the SN curve of the solder joint material is obtained by the steps of: Before setting the load test condition and determining the fatigue limit load of the test material based on the step-by-step method to obtain the relationship between the weld point force and the test cycle number of the test material, it further comprises: ​ Determining the type and thickness of the test material, determining the sample size, clamp and weld point diameter according to the testing machine, selecting the number of test materials and the cycle base, and setting the stress ratio for use in the weld point test process.

3. The method for obtaining the SN curve of solder joint material as described in claim 2, characterized in that, The steps of determining the fatigue limit load of the test material based on the step-by-step method include: Setting a load level and a load increment of the test material, and repeating the following steps: Based on the load level and the cycle base, the limit load test of the current test material is performed, and according to the limit load test result: If the limit load test result of the current test material is failure, the load level of the limit load test of the next test material is reduced by one level based on the load increment; If the limit load test result of the current test material is exceeded, the load level of the limit load test of the next test material is increased by one level based on the load increment; If the limit load test result of the current test material is base metal non-heat affected zone fracture, the current test data is invalid.

4. The method for obtaining the SN curve of solder joint material as described in claim 3, characterized in that, The strain gauge patch positions should satisfy that the distance from the weld point is within the range of the heat affected zone, and the distance from the weld point is not less than a preset multiple of the strain gauge width.

5. The method for obtaining the SN curve of solder joint material as described in claim 4, characterized in that, After calculating the strain gauge patch positions of multiple points near the weld point to calculate the strain at the weld point, it further comprises: Based on the calculated strain gauge patch positions, the test strain-time history data of the strain gauges along the load test tensile direction are collected during the weld point test process.

6. The method for obtaining the SN curve of solder joint material as described in claim 5, characterized in that, The steps of loading a unit force consistent with a load test direction in the simulation model to calculate a strain at the strain gauge patch positions near the weld point include: Loading a unit force consistent with a load test direction in the simulation model to output a weld point unit force; In the fatigue calculation software, the weld unit force is superimposed on the test load spectrum, and the stress at the strain gauge patch position is output; The output stress at the strain gauge patch position is converted into the strain at the strain gauge patch position.

7. The method of claim 6, wherein the SN curve of the solder joint material is obtained by the steps of: The weld unit stress is obtained based on the output weld unit force, and the specific steps include: ​ In the fatigue calculation software, the output weld unit force is superimposed on the forces at each level of the weld test to obtain the weld unit stress.

8. A solder joint material SN curve acquisition apparatus characterized by comprising: It includes: A determination module for determining the fatigue limit load of the test material based on the set load test conditions and the step method, and obtaining the relationship between the weld force and the test cycle number of the test material; A calculation module for calculating the strain gauge patch position near the weld by simulating the weld test, calculating the strain at the weld, and loading a unit force consistent with the load test direction in the simulation model according to the fatigue limit load determined by the determination module, and calculating the strain at the strain gauge patch position near the weld; An execution module for correcting the weld simulation model based on the strain at the weld and the strain at the strain gauge patch position calculated by the calculation module, loading a unit force consistent with the load test direction, outputting the weld unit force, and obtaining the weld unit stress based on the output weld unit force; Based on the weld unit force and the weld unit stress, the weld unit force-stress relationship is obtained, and combined with the weld point-cycle number relationship, the weld material SN curve is obtained; The correction of the weld simulation model further includes: The calculated strain at the weld and the strain at the strain gauge patch position near the weld are compared, and the weld finite element model is corrected to ensure that the strain at the weld and the strain at the strain gauge patch position near the weld are consistent to more than a preset value.

9. A solder joint material SN curve acquisition apparatus according to claim 8, wherein Before determining the relationship between the weld force and the test cycle number of the test material based on the set load test conditions and the step method to determine the fatigue limit load of the test material, it also includes: Determine the type and thickness of the test material, determine the sample size, clamp and weld diameter according to the testing machine, select the number of test materials and the cycle base, and set the stress ratio for use in determining the fatigue limit load of the test material.

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