Testing method for obtaining material fracture property based on 0.5t-CT specimen reconstruction technology

Abstract

The present invention belongs to the technical field of mechanical property test for metallic materials, and particularly relates to a testing method for obtaining material fracture property based on 0.5T-CT specimen reconstruction technology. A testing method for obtaining material fracture property based on 0.5T-CT specimen reconstruction technology, including the following steps: preparing a 0.5T-CT original specimen from parent material, conducting fracture property test to obtain tested 0.5T-CT specimen remnant; performing testing analysis on parent material, to obtain the full-process equivalent stress-strain relation curve of parent material; determining the range of the material available for preparing reconstructed specimen; performing specimen reconstruction with the reusable material and auxiliary material through welding to obtain 0.5T-CT reconstructed specimen; conducting testing analysis on weld material to obtain stress-strain relation curve of weld material; determining fracture parameters of 0.5T-CT reconstructed specimen; performing fracture toughness test on 0.5T-CT reconstructed specimen based on fracture parameters to obtain fracture property of parent material and / or weld material. The testing method of the present invention is simple and the test result is accurate.

Description

A testing method for obtaining material fracture properties based on 0.5T-CT specimen reconstruction technology Technical Field

[0001] The present invention belongs to the technical field of testing the mechanical properties of metal materials, and in particular relates to a testing method for obtaining the fracture properties of materials based on 0.5T-CT sample reconstruction technology. Background Art

[0002] To monitor the degree of neutron irradiation embrittlement of the reactor pressure vessel (RPV) in nuclear power plants, RPV irradiation surveillance samples are placed near the inside of the RPV. By regularly extracting surveillance samples and completing hot chamber tests, the fracture toughness of the RPV material is determined. This allows the RPV's lifespan against rapid brittle fracture to be evaluated, and the PT curve (pressure-temperature limit curve) that guides RPV startup and shutdown, hydrostatic testing, and normal operation is determined. This is crucial for nuclear power plants and is highly valued by the industry.

[0003] However, during the renewal phase of a nuclear power plant's operating license, there may be a shortage of surveillance samples. Therefore, to address the practical engineering challenge of insufficient samples, attempts are being made to place spent surveillance sample remnants back into the reactor pressure vessel for continued irradiation. These remnants can then be removed and reassembled into new surveillance samples for reuse when necessary.

[0004] Specimen reassembly technology can effectively utilize limited irradiated monitoring materials to obtain material fracture toughness data corresponding to longer service life. For example, Chinese invention patent CN201410060019.5 discloses a method for determining the minimum insertion segment size in Charpy impact specimen reassembly technology. However, the method for preparing Charpy impact reassembly specimens and judging the performance of reassembly specimens proposed in this patent are only applicable to Charpy specimens for obtaining impact performance, and cannot be applied to compact tensile specimens. For another example, Chinese invention patent CN202210846785.9 discloses a method for preparing reassembly compact tensile specimens. This patent proposes obtaining the insertion segment range based on DIC technology and proposes a new method for preparing specimens, but does not mention the selection of welding parameters and the method for obtaining the fracture parameters of reassembly specimens.

[0005] Summary of the Invention

[0006] In view of this, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a testing method for obtaining the fracture properties of materials based on 0.5T-CT specimen reconstruction technology, which is suitable for the fracture toughness test of reactor pressure vessel materials in pressurized water reactor nuclear power plants.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A testing method for obtaining material fracture properties based on 0.5T-CT specimen reconstruction technology includes the following steps:

[0009] Prepare 0.5T-CT original specimens of the parent material, carry out fracture performance tests, and obtain residual 0.5T-CT specimens after the test;

[0010] Conducting a full-process equivalent stress-strain relationship curve test and analysis on the base material during proportional stretching-yielding-strengthening-necking-breaking to determine the full-process equivalent stress-strain relationship curve;

[0011] Calculating the size of the plastic zone at the crack tip of the sample remnant to determine the range of materials that can be used to prepare the reconstituted sample;

[0012] Cutting out the non-plastic deformation areas on both sides of the sample residue to form a reusable material, and reconstructing the sample by welding the reusable material and the auxiliary material to obtain a 0.5T-CT reconstructed sample;

[0013] Conduct stress-strain curve testing and analysis on the weld material to obtain the stress-strain curve of the weld material;

[0014] Determining the fracture parameters of the 0.5T-CT reconstructed specimen based on the full-process equivalent stress-strain curve and the stress-strain curve of the weld material;

[0015] Based on the fracture parameters, a fracture toughness test of a 0.5T-CT reconstructed specimen is carried out to obtain the fracture properties of the base material and / or the weld material.

[0016] According to some preferred implementation aspects of the present invention, in the test and analysis of the full-range equivalent stress-strain relationship curve of the base material, the full-range equivalent stress-strain relationship curve is iterated in combination with a finite element iterative analysis method until the load-displacement curve of the tensile specimen obtained by combining the full-range equivalent stress-strain relationship curve with the finite element iterative analysis method coincides with the load-displacement curve obtained by the tensile test, thereby determining the full-range equivalent stress-strain curve.

[0017] Specifically, in some embodiments, the stress-strain relationship of the material obtained based on the uniaxial tensile test is input into the finite element as the initial constitutive relationship, and the load-displacement relationship of the funnel specimen is calculated, and it is iterated with the load-displacement relationship of the funnel specimen obtained from the experiment; the input stress-strain relationship is further updated until the load-displacement relationship of the funnel specimen obtained based on the finite element calculation basically coincides with the load-displacement relationship obtained from the experiment. At this time, the input stress-strain relationship is the full-process equivalent stress-strain relationship of the material.

[0018] According to some preferred implementation aspects of the present invention, in the calculation of the size of the plastic zone at the crack tip of the 0.5T-CT original specimen, the determined full-range equivalent stress-strain curve is used as the constitutive relation of the base material for finite element input.

[0019] According to some preferred embodiments of the present invention, the range of materials that can be used for reconstructed specimen preparation is determined, and the full-range equivalent stress-strain curve is determined by finite element iterative analysis method, and then the precise position and size of the non-plastic deformation area used for 0.5T-CT reconstructed specimen preparation is calculated.

[0020] According to some preferred embodiments of the present invention, the welding is performed using electron beam welding, and the arc starting point during the welding process is located outside the reusable material region. In some embodiments, the welding parameters are: accelerating voltage 140-160 kV, focusing current 1200-1400 mA, welding current 10-25 mA, and welding speed 900-1100 mm / min. Preferably, the accelerating voltage is 150 kV, focusing current 1300 mA, welding current 10-25 mA, and welding speed 1000 mm / min.

[0021] According to some preferred embodiments of the present invention, the total width of the weld and the heat-affected zone is about 2.376 mm.

[0022] According to some preferred embodiments of the present invention, the auxiliary material is a material of the same type as the parent material.

[0023] According to some preferred implementation aspects of the present invention, the fracture parameters include stress intensity factor K and J integral J.

[0024] According to some preferred embodiments of the present invention, the J integral J includes the elastic J integral Je; and determining the J integral J and the stress intensity factor K in the fracture parameters of the 0.5T-CT reconstructed specimen comprises the following steps:

[0025] Based on the full-process equivalent stress-strain curve and the stress-strain curve of the weld material, and combined with the energy equivalence principle, the load P and elastic displacement h of the 0.5T-CT reconstructed sample are derived. e , elastic strain energy U e The relationship between:

[0026] Where, represents the characteristic elastic strain energy, P e * represents the characteristic elastic load, P e * =k0EA * ; V *represents the characteristic volume, V * =A * h * ;h * represents the characteristic displacement of the 0.5T-CT reconstructed sample; A * represents the characteristic area of ​​the 0.5T-CT reconstitution sample; P represents the load; h e represents elastic displacement, U e represents elastic strain energy;

[0027] The strain energy U is obtained from formula (1): e The relationship with load P is:

[0028] Combined with the energy definition of J integral J We can get:

[0029] Where U represents the crack tip energy, B represents the thickness of the 0.5T-CT reconstructed specimen, a represents the crack length, P represents the load, k0 represents the undetermined coefficient, and E represents the elastic modulus of the material; the material includes the base material and / or the weld material;

[0030] The elastic J integral Je is equal to the energy G and can be obtained by converting the stress intensity factor K. The relationship between the elastic J integral Je and the stress intensity factor K is:

[0031] Where, E' represents the equivalent elastic modulus of the material; Je represents the elastic J integral J; K represents the stress intensity factor; G represents energy;

[0032] According to the relationship between the elastic J integral Je and the stress intensity factor K, the calculation formula of the stress intensity factor K is obtained:

[0033] A finite element model of the 0.5T-CT reconstructed specimen was established, and elastic finite element simulation analysis was performed on the 0.5T-CT reconstructed specimen. Load and displacement data were extracted, and the undetermined coefficient k0 of equations (3) and (5) was calibrated to determine equations (3) and (5).

[0034] The J integral J and the stress intensity factor K are obtained by performing calculations according to the determined formulas (3) and (5).

[0035] According to some preferred embodiments of the present invention, the J integral J includes a pure plastic J integral Jp; and determining the pure plastic J integral Jp of the 0.5T-CT reconstructed specimen fracture parameters includes the following steps:

[0036] According to the energy equivalence principle, the load P, displacement h and pure plastic deformation energy U of the 0.5T-CT reconstructed specimen are derived.p The relationship between:

[0037] Among them, the characteristic plastic strain energy U p * , characteristic load P p * , characteristic index m p They can be expressed as:

[0038] Wherein, k1 represents the first undetermined coefficient; k2 represents the second undetermined coefficient; k3 represents the third undetermined coefficient; k4 represents the fourth undetermined coefficient; the first undetermined coefficient, the second undetermined coefficient, the third undetermined coefficient and the fourth undetermined coefficient can be obtained by finite element analysis; K R Indicates material coefficient; N indicates material index; V * Represents the characteristic volume of the sample; V * =h * A * ;h * represents the characteristic displacement of the specimen, A * Indicates the characteristic area of ​​the specimen;

[0039] For 0.5T-CT reconstructed samples,

[0040] Where W represents the width of the 0.5T-CT reconstructed specimen; B represents the thickness of the 0.5T-CT reconstructed specimen; α represents the crack length of the 0.5T-CT reconstructed specimen; m represents the effective volume reduction parameter related to the crack length of the 0.5T-CT reconstructed specimen;

[0041] Substituting into equations (6) and (7), we can obtain the pure plastic deformation performance U p Relationship with load P:

[0042] Combined with the J integral J energy U definition The calculation formula of pure plastic J integral Jp of the specimen can be obtained:

[0043] During the pre-processing of the finite element software, the tensile mechanical parameters of the material are input, and the load-displacement curves under different a / W conditions are calculated. After geometrically independent processing (P / A*-h / h*), the parameter m can be obtained. Pure plastic calculation is performed on the original sample. According to formula (6), P under different stress hardening levels can be obtained. p *, m p , and then calibrate with formula (7) to obtain the first undetermined coefficient, the second undetermined coefficient, the third undetermined coefficient and the fourth undetermined coefficient, thereby determining formula (10);

[0044] The pure plastic J integral Jp is calculated using the determined formula (10).

[0045] According to some preferred embodiments of the present invention, stress-strain relationship data of the weld material is obtained by an indentation method, and the full-range stress-strain data of the base material at different temperatures and the stress-strain relationship data of the weld material are input into a finite element model of a 0.5T-CT reconstructed specimen containing a weld to carry out calculations, thereby obtaining a load-displacement curve and a J-integral J considering differences in material properties by finite element calculations;

[0046] Analytical J integral J and standard formula calculation J 标准试样 The proportional relationship between the integrals is used to calibrate the proportional coefficient β of formula (11);

[0047] Based on formula (11), the calculation formula of the J integral J of the fracture parameter can be obtained, and then the J integral J of the fracture parameter can be obtained;

[0048] Where, J represents the J integral of the crack tip of the 0.5T-CT reconstructed specimen, J, 标准试样 represents the crack tip J integral J calculated by the standard formula of the parent material, β represents the proportional coefficient, F represents the loading load, B represents the specimen thickness, and B N represents the net thickness of the specimen, a represents the crack length after 0.5T-CT reconstruction, W represents the crack width after 0.5T-CT reconstruction, E represents the equivalent elastic modulus, v represents the Poisson's ratio, η p represents the plasticity factor, U p represents the plastic deformation energy of the 0.5T-CT reconstructed specimen after loading, and a0 represents the initial crack length of the 0.5T-CT reconstructed specimen.

[0049] Compared with the prior art, the present invention is beneficial in that:

[0050] The present invention discloses a testing method for obtaining material fracture properties based on 0.5T-CT specimen reconstruction technology. By testing the full-process equivalent stress-strain curve of the material at different temperatures and combining it with finite element-assisted testing technology to obtain the distribution law of the plastic zone at the crack tip, the reusable range of the residual sample after the 0.5T-CT specimen fracture test is accurately determined. The 0.5T-CT reconstructed specimen is prepared by welding, and a calculation method for the fracture parameters of the 0.5T-CT reconstructed specimen is determined based on the principles of fracture mechanics and elastic-plastic finite element-assisted testing methods. The fracture properties of the 0.5T-CT reconstructed specimen can be effectively obtained. The fracture test results of the reconstructed specimen and the parent material are relatively consistent, which can effectively increase the material utilization rate by 3 times. The testing method of the present invention is simple and the test results are accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0052] FIG1 is a schematic structural diagram of a 0.5T-CT sample in a preferred embodiment of the present invention;

[0053] FIG2 is a schematic diagram of welding a reconstructed sample in a preferred embodiment of the present invention;

[0054] FIG3 is a schematic structural diagram of a funnel sample in a preferred embodiment of the present invention;

[0055] FIG4 is an equivalent full-range stress-strain curve of the material at -20°C in a preferred embodiment of the present invention;

[0056] FIG5 is a finite element mesh model of a 0.5T-CT original sample in a preferred embodiment of the present invention;

[0057] FIG6 is a schematic diagram of the size of the plastic zone at the crack tip of a 0.5T-CT specimen at -20°C in a preferred embodiment of the present invention;

[0058] FIG7 is a load-displacement diagram of the fracture test of 0.5T-CT original specimen and reconstructed specimen in a preferred embodiment of the present invention;

[0059] FIG8 is a finite element mesh model of a 0.5T-CT reconstructed specimen in a preferred embodiment of the present invention;

[0060] FIG9 is a comparison diagram of the fracture test results of the 0.5T-CT original sample and the reconstructed sample in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0062] The present invention's method for testing material fracture properties using 0.5T-CT specimen reconstitution technology includes four steps: testing material fracture properties using the original 0.5T-CT specimen, obtaining the full-process equivalent stress-strain curve of the (parent) material, determining the range of materials that can be used to prepare reconstituted specimens using the original 0.5T-CT specimen, and finally testing the material fracture properties using the reconstituted 0.5T-CT specimen. 0.5T-CT stands for Compact Tensile.

[0063] Specifically, the testing method for obtaining material fracture properties based on 0.5T-CT sample reconstruction technology in this embodiment includes the following steps:

[0064] Step (a), preparing a 0.5T-CT original sample of the parent material, carrying out a fracture performance test, and obtaining a 0.5T-CT sample residual sample after the test.

[0065] For the research material, the fracture toughness 0.5T-CT original specimen was prepared. The loading and structure diagram is shown in Figure 1, where P is the loading load, V LL is the loading linear displacement of the 0.5T-CT specimen, B is the specimen thickness, and b is the remaining ligament length. The left side of Figure 1 is the main view of the structure, and the right side of Figure 1 is the left view of the structure.

[0066] Step (b) testing and analyzing the full-process equivalent stress-strain curve of the base material during proportional stretching-yielding-strengthening-necking-breaking to obtain the full-process equivalent stress-strain curve of the base material.

[0067] The full-range equivalent stress-strain curve test specimen of the parent material is a funnel rod specimen (as shown in Figure 3). It is necessary to combine the auxiliary finite element iterative analysis method until the load-displacement curve of the standard tensile specimen calculated based on the full-range equivalent stress-strain curve input by the finite element is basically consistent with the tensile load-displacement curve obtained by the test, and then obtain the full-range stress-strain curve of the specimen until it breaks. At least three effective specimens must be tested for tensile testing.

[0068] Among them, proportional stretching-yielding-strengthening-necking-fracture is the entire process of equivalent stress-strain.

[0069] Specifically, in this embodiment, the stress-strain relationship obtained based on the uniaxial tensile test is first input into the finite element as the initial constitutive relationship, and the load-displacement relationship of the funnel specimen is calculated, and it is iterated with the load-displacement relationship of the funnel specimen obtained from the experiment; secondly, the input stress-strain relationship is further updated until the load-displacement relationship of the funnel specimen obtained based on the finite element calculation basically coincides with the load-displacement relationship obtained from the experiment. At this time, the input stress-strain relationship is the full-process equivalent stress-strain relationship of the material.

[0070] In some executable embodiments, in the test and analysis of the full-range equivalent stress-strain relationship curve of the base material, the full-range equivalent stress-strain relationship curve is iterated in combination with the finite element iterative analysis method until the load-displacement curve of the tensile specimen obtained by combining the full-range equivalent stress-strain relationship curve with the finite element iterative analysis method coincides with the curve obtained by the tensile test, thereby determining the full-range equivalent stress-strain curve.

[0071] Step (c) calculates the size of the plastic zone at the crack tip of the original sample to determine the range of materials that can be used to prepare the reconstructed sample.

[0072] Specifically, the size of the plastic zone at the crack tip of the original 0.5T-CT specimen was calculated using the full-scale equivalent stress-strain curve of the parent material as input into the material's constitutive relationship. Within the range of materials suitable for reconstructed specimen preparation, the full-scale equivalent stress-strain curve of the parent material obtained through iterative finite element analysis was used to calculate the precise location and size of the non-plastic deformation zone used in reconstructed specimen preparation.

[0073] In some embodiments, before step (c), the method further includes conducting a fracture toughness test on a 0.5T-CT original sample.

[0074] Specifically, the fracture toughness test on the surface of the 0.5T-CT specimen was carried out in accordance with GB / T 21143-2014, and the real-time crack length of the specimen was measured using the load separation method recommended in Appendix J.

[0075] Step (d): cutting out the non-plastic deformation areas on both sides of the 0.5T-CT sample residue (areas outside the plastic zone at the crack tip) to form a reusable material, and recombining the reusable material with the auxiliary material by welding to obtain a 0.5T-CT reconstructed sample.

[0076] The welding is electron beam welding, and the sample is reassembled with reference to the welding method shown in Figure 2. The welding method in Figure 2 has three welds, one is a vertical weld, and two are horizontal welds. On the right side of the vertical weld and between the two horizontal welds, there are reusable materials and auxiliary materials. The reusable material is closer to the vertical weld, and the auxiliary material is on the right side of the reusable material. Except for the reusable material here, all other places are auxiliary materials. And no welding is performed between the reusable material between the two horizontal welds and the auxiliary material on its right side. Through the welding method in Figure 2, the arc starting points during the welding process are all located outside the reusable material area, avoiding the influence of residual stress on the sample.

[0077] In some other executable embodiments, the total width of the weld and the heat-affected zone is relatively small, not exceeding 3 mm. The auxiliary material and the reused material have similar mechanical properties, and are preferably the parent material.

[0078] After welding and reassembling the auxiliary material and the reused material as shown in Figure 2, a 0.5T-CT reassembly specimen was prepared according to the structure in Figure 1, with some initial cracks and their tips located on the reused material. This allowed the material in the non-plastic deformation region to be reassembled into two or more specimens, increasing material utilization by three times or more.

[0079] Step (e) testing and analyzing the stress-strain curve of the weld material to obtain the stress-strain curve of the weld material.

[0080] Specifically, the weld material is the material of the weld formed by welding the auxiliary material and the reused material, and is usually a mixed material formed by welding the auxiliary material and the reused material.

[0081] The welding parameters in this embodiment are: accelerating voltage 150 kV, focusing current 1300 mA, welding current 10-25 mA, and welding speed 1000 mm / min. In other embodiments, the welding parameters are preferably: accelerating voltage 140-160 kV, focusing current 1200-1400 mA, welding current 10-25 mA, and welding speed 900-1100 mm / min. The welding method and corresponding welding parameters shown in Figure 2 reduce the heat-affected zone (HAZ) and weld residual stress, minimizing the impact of welding on the stress-strain field at the crack tip.

[0082] Step (f): determining the fracture parameters of the 0.5T-CT reconstructed specimen based on the full-process equivalent stress-strain curve of the base material and the stress-strain curve of the weld material.

[0083] The fracture parameters include the stress intensity factor K and the J integral J. The full-process equivalent stress-strain curve of the material obtained in step (b) is used as the input of the material constitutive relationship. Based on the fracture mechanics theory and elastic-plastic finite element-assisted analysis technology, the coefficients of the fracture parameter calculation formula of the 0.5T-CT reconstructed specimen are determined, so that the fracture parameters at the crack tip are calculated accurately and reliably, eliminating the influence of welding on the reconstructed specimen.

[0084] Furthermore, the J-integral J includes the elastic J-integral Je and the purely plastic J-integral Jp. Depending on the application scenario and material, the fracture parameter may include only the stress intensity factor K, or include the elastic J-integral Je and the stress intensity factor, or include the purely plastic J-integral Jp, or all three.

[0085] In some embodiments, the J integral J includes an elastic J integral J e Determining the J integral J and stress intensity factor K in the fracture parameters of the 0.5T-CT reconstructed sample comprises the following steps:

[0086] Based on the full-process equivalent stress-strain curve of the parent material and the stress-strain curve of the weld material, and combined with the energy equivalence principle, the load P and elastic displacement h of the 0.5T-CT reconstructed specimen are derived. e , elastic strain energy U e The relationship between:

[0087] Where, represents the characteristic elastic strain energy, P e * represents the characteristic elastic load, P e * =k0EA * ; V * represents the characteristic volume, V * =A * h * ;h * represents the characteristic displacement of the 0.5T-CT reconstructed sample; A * represents the characteristic area of ​​the 0.5T-CT reconstitution sample; P represents the load; h e represents elastic displacement, U e represents the elastic strain energy.

[0088] The strain energy U is obtained from formula (1): e The relationship with load P is:

[0089] Combined with the energy definition of J integral J We can get:

[0090] Where U represents the crack tip energy, B represents the thickness of the 0.5T-CT reconstructed specimen, α represents the crack length, P represents the load, k0 represents the undetermined coefficient, and E represents the elastic modulus of the material; the material includes the base material and / or the weld material;

[0091] The elastic J-integral Je, which represents the elastic part of the J-integral J, is equal to the energy G and can be obtained by converting the stress intensity factor K. The relationship between the elastic J-integral Je and the stress intensity factor K is:

[0092] Furthermore, the stress intensity factor K is a stress intensity factor.

[0093] Where, E′ represents the equivalent elastic modulus of the material; J e represents the elastic J integral J; K represents the stress intensity factor; G represents energy.

[0094] Then the calculation formula of the stress intensity factor K of the 0.5T-CT reconstructed sample is obtained:

[0095] A finite element model of the reconstructed specimen was established, and elastic finite element simulation analysis was performed on it. Load and displacement data were extracted, and the undetermined parameters of equation (1) were calibrated to obtain the expression for the stress intensity factor K of the 0.5T-CT reconstructed specimen. The stress intensity factor K of the 0.5T-CT reconstructed specimen can be obtained by calculation using equation (5).

[0096] Furthermore, the elastic J integral Je of the 0.5T-CT reconstructed sample is calculated using formula (3).

[0097] The J-integral J includes the pure plastic J-integral Jp. The determination of the pure plastic J-integral Jp of the fracture parameters of the 0.5T-CT reconstructed specimen includes the following steps:

[0098] According to the energy equivalence principle, the load P, displacement h and pure plastic deformation energy U of the 0.5T-CT reconstructed specimen are derived. p The relationship between:

[0099] Among them, the characteristic plastic strain energy U p * , characteristic load P p * , characteristic index m p They can be expressed as:

[0100] Wherein, k1 represents the first undetermined coefficient; k2 represents the second undetermined coefficient; k3 represents the third undetermined coefficient; k4 represents the fourth undetermined coefficient; the first undetermined coefficient, the second undetermined coefficient, the third undetermined coefficient and the fourth undetermined coefficient can be obtained by finite element analysis; K R Indicates material coefficient; N indicates material index; V * Represents the characteristic volume of the cracked specimen, V * =h * A * , h * represents the characteristic displacement of the specimen, A * represents the characteristic area of ​​the specimen, W and B represent the width and thickness of the specimen, respectively, and m represents the effective volume reduction parameter related to the crack length a of the specimen.

[0101] For the 0.5T-CT reconstitution sample, it is assumed that:

[0102] Where W represents the width of the 0.5T-CT reconstructed specimen; B represents the thickness of the 0.5T-CT reconstructed specimen; α represents the crack length of the 0.5T-CT reconstructed specimen; and m represents the effective volume reduction parameter related to the crack length of the 0.5T-CT reconstructed specimen.

[0103] Substituting into equations (6) and (7), we can obtain the pure plastic deformation performance U p Relationship with load P:

[0104] Combined with the energy definition of J integral J The pure plastic J integral J of the specimen can be obtained p Calculation formula:

[0105] During the pre-processing of the finite element software, the tensile mechanical parameters of the material are input, and the load-displacement curves under different a / W conditions are calculated. After geometrically independent processing (P / A*-h / h*), the parameter m can be obtained. Pure plastic calculation is performed on the specimen, and according to formula (6), P under different stress hardening levels can be obtained. p *, m p , and then calibrate with formula (7) to obtain the first undetermined coefficient, the second undetermined coefficient, the third undetermined coefficient and the fourth undetermined coefficient, thereby determining formula (10).

[0106] Specifically, the material tensile mechanical parameters include hardness, yield, strength, and fracture. Depending on the needs of calculating the J formula, one or more of these parameters can be selected and input into the finite element software before processing to participate in the finite element calculation.

[0107] The pure plastic J-integral Jp can be obtained by using formula (10) after determining the first, second, third and fourth unknown coefficients and combining it with other collected physical parameters.

[0108] In some feasible embodiments, the stress-strain relationship data of the weld material is obtained by the indentation method, and the full-range stress-strain data of the base material at different temperatures and the stress-strain relationship data of the weld material are input into the finite element model of the 0.5T-CT reconstructed specimen containing the weld to carry out calculations, and then the finite element calculation is used to obtain the load-displacement curve and the J integral J considering the difference in material properties.

[0109] Analysis of the J integral of fracture parameters and calculation of the J integral by the standard formula 标准试样 There is a proportional relationship between them, and the proportional coefficient β of formula (11) is calibrated;

[0110] Based on formula (11), the calculation formula of the J-integral J of the fracture parameter can be obtained, and then the J-integral J of the fracture parameter can be obtained.

[0111] Where, J is the J integral of the crack tip of the reconstructed specimen, J, 标准试样 is the J integral of the crack tip of the parent material standard specimen, β is the proportional coefficient, F is the loading load, B is the specimen thickness, and B Nis the net thickness of the specimen, a and W are the crack length and width of the specimen, E is the equivalent elastic modulus, v is the Poisson's ratio, η p represents the plasticity factor, U p represents the plastic deformation energy of the sample loaded, and a0 is the initial crack length of the sample.

[0112] Furthermore, the standard formula is (11) 标准试样 The corresponding formula is: The parent material standard specimen includes the original specimen.

[0113] Step (g): Based on the determined fracture parameters of the 0.5T-CT reconstructed sample, a fracture toughness test is conducted on the 0.5T-CT reconstructed sample to obtain the fracture properties of the material. The test results are verified to be representative of the fracture properties of the original material.

[0114] Conduct fracture toughness testing on reconstructed 0.5T-CT specimens. The fracture toughness testing method for reconstructed specimens should fully account for the influence of material heterogeneity across the weld seam, and the reliability of the crack length measurement method during the test must be verified. Therefore, the fracture performance parameters of the reconstructed specimens must be determined based on the fracture parameter calculation formulas applicable to the reconstructed specimens determined in step (f). These fracture parameters include the J-integral (J) and the stress intensity factor (K), which are determined based on test requirements.

[0115] In an embodiment of a test method for obtaining material fracture properties based on 0.5T-CT specimen reconstruction technology, the following steps are included:

[0116] Step (1): Material fracture performance test based on 0.5T-CT original sample.

[0117] For metal materials, a 0.5T-CT specimen was processed according to the structure shown in Figure 1, and the J-integral J-Δa curve of the material at -20°C was obtained with reference to the GB / T 21143-2014 standard.

[0118] Step (2): Obtain the equivalent stress-strain curve of the base material throughout the entire process.

[0119] Funnel specimens were processed according to the structure shown in Figure 3, and tensile tests were carried out at -20°C. Combined with the tensile test of standard round bar specimens, the auxiliary finite element iterative analysis method was used to obtain the full-range stress-strain relationship curve of the base material at -20°C until fracture, as shown in Figure 4.

[0120] In some other embodiments, other standard styles may be combined according to the needs of the scenario, such as plate tensile specimen test, straight round bar tensile specimen test, etc.

[0121] In step (3), the range of materials that the 0.5T-CT original sample can be used to prepare the reconstituted sample is determined.

[0122] The stress-strain curve obtained in step (2) for the entire process of the parent material at -20°C until fracture was used as the material constitutive relation and input into the finite element method. The finite element model of the 0.5T-CT specimen was established as shown in Figure 5. The size distribution of the plastic zone at the crack tip of the 0.5T-CT specimen under different load levels was calculated. As shown in Figure 6, the origin of the coordinate represents the crack tip, λ = P / (σ0Bb), representing the dimensionless load level, where P is the loading load, σ0 is the material yield stress, β is the specimen thickness, and b is the remaining ligament length. The size of the plastic zone is calculated based on the loading load given in Figure 6, and the range available for specimen reorganization is then determined.

[0123] Step (4), testing the stress-strain relationship data of the weld material. The stress-strain relationship data of each micro-area of ​​the weld material are obtained by the indentation method.

[0124] Step (5): Material fracture performance testing technology based on 0.5T-CT reconstructed specimens.

[0125] The load-displacement curve of the fracture test of the 0.5T-CT reconstructed specimen was collected, as shown in Figure 7. The stress-strain relationship curve of the material at -20°C until fracture obtained in step (2) was input into the finite element as the material constitutive relationship. The finite element mesh model of the 0.5T-CT reconstructed specimen was established as shown in Figure 8. The corresponding parameters were input and the load-displacement curves under different a / W conditions were calculated. After geometrically independent processing (P / A*-h / h*), the parameter m was obtained. Pure plastic calculation was performed on the specimen. According to formula (6), Pp* and mp at different stress hardening levels were obtained. Combined with formula (7), k1 to k4 can be calibrated and the corresponding fracture parameters can be obtained.

[0126] The proportional coefficient β in Equation (11) is obtained by finite element calibration to be 0.88, and the fracture parameters of the 0.5T-CT reconstructed specimen can be calculated.

[0127] Furthermore, through experiments, the material J-integral J-Δa curve of the 0.5T-CT reconstructed sample was obtained. Figure 9 shows the fracture J-integral J-Δa curves of the 0.5T-CT original sample and the reconstructed sample at -20°C. It can be seen that the material fracture properties obtained based on the 0.5T-CT reconstructed sample can effectively characterize the fracture properties of the parent material.

[0128] The present invention provides a testing method for obtaining material fracture properties based on 0.5T-CT sample reconstitution technology, comprising the following steps: (a) preparing a 0.5T-CT original sample of a parent material, conducting a fracture property test, and obtaining a 0.5T-CT sample residual sample after the test; (b) conducting a full-process equivalent stress-strain relationship curve test and analysis on the parent material to obtain a full-process equivalent stress-strain relationship curve of the parent material; (c) calculating the size of the plastic zone at the crack tip of the original sample to determine the range of materials that can be used to prepare the reconstituted sample; (d) cutting out the non-plastic deformation areas on both sides of the sample to form a The reusable material is reassembled into a reusable material by welding the reusable material and the auxiliary material to obtain a 0.5T-CT reconstructed specimen; (e) the stress-strain curve of the weld material is tested and analyzed to obtain the stress-strain curve of the weld material; (f) the fracture parameters of the 0.5T-CT reconstructed specimen are determined based on the full-range equivalent stress-strain curve of the base material and the stress-strain curve of the weld material; (g) based on the fracture parameters, a fracture toughness test is carried out on the 0.5T-CT reconstructed specimen to obtain the fracture properties of the base material and / or weld material. The present invention conducts full-process equivalent stress-strain curve testing of materials at different temperatures, combines finite element-assisted testing technology to obtain the distribution law of the plastic zone at the crack tip, accurately determines the reuse range of residual samples after the 0.5T-CT specimen is subjected to fracture testing, prepares 0.5T-CT reconstructed specimens by welding, and determines the fracture parameter formula of the 0.5T-CT reconstructed specimens based on the principles of fracture mechanics and elastic-plastic finite element-assisted testing methods. The fracture performance of the 0.5T-CT reconstructed specimens can be effectively obtained, and the fracture test results of the parent material are relatively consistent, which can effectively increase the material utilization rate by 3 times. The testing method of the present invention is simple and the test results are accurate.

[0129] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A testing method for obtaining material fracture properties based on 0.5T-CT sample reconstruction technology, characterized in that: The steps include: Prepare the original 0.5T-CT specimen of the parent material, carry out the fracture performance test, and obtain the residual 0.5T-CT specimen after the test; Conducting a test analysis on the full-process equivalent stress-strain relationship curve of proportional stretching-yielding-strengthening-necking-breaking on the base material to determine the full-process equivalent stress-strain relationship curve; Calculating the size of the plastic zone at the crack tip of the sample remnant to determine the range of materials that can be used to prepare the reconstituted sample; Cutting out the non-plastic deformation areas on both sides of the sample residue to form a reusable material, and recombining the sample by welding the reusable material and the auxiliary material to obtain a 0.5T-CT recombined sample; Conduct stress-strain curve testing and analysis on the weld material to obtain the stress-strain curve of the weld material; Based on the full-range equivalent stress-strain relationship curve and the stress-strain relationship curve of the weld material, determining the fracture parameters of the 0.5T-CT reconstructed sample; Based on the fracture parameters, a fracture toughness test of a 0.5T-CT reconstructed specimen is carried out to obtain the fracture properties of the base material and / or the weld material.

2. The testing method according to claim 1, characterized in that: In the test and analysis of the full-range equivalent stress-strain relationship curve for the base material, the full-range equivalent stress-strain relationship curve is iterated in combination with the finite element iterative analysis method until the load-displacement curve of the tensile specimen obtained by combining the full-range equivalent stress-strain relationship curve with the finite element iterative analysis method coincides with the curve obtained by the tensile test, thereby determining the full-range equivalent stress-strain curve.

3. The testing method according to claim 2, characterized in that: In the calculation of the size of the plastic zone at the crack tip of the 0.5T-CT original sample, the determined full-range equivalent stress-strain curve is used as the constitutive relation of the parent material for finite element input.

4. The testing method according to claim 2, characterized in that: The determined range of materials that can be used for reconstructed specimen preparation is used to obtain the full-range equivalent stress-strain curve using the finite element iterative analysis method, and then calculate the precise position and size of the non-plastic deformation area used for 0.5T-CT reconstructed specimen preparation.

5. The testing method according to claim 1, characterized in that: The welding is electron beam welding, the arc starting point during the welding process is located outside the reusable material area, the welding temperature during the welding process does not exceed 300° C., and the total width of the weld and the heat affected zone does not exceed 3 mm.

6. The testing method according to claim 1, characterized in that: The auxiliary material is the same type of material as the parent material.

7. The testing method according to claim 1, characterized in that: The fracture parameters include stress intensity factor K and / or J integral J.

8. The testing method according to claim 7, characterized in that: The J integral J includes the elastic J integral J e ; Determining the J integral J and the stress intensity factor K in the fracture parameters of the 0.5T-CT reconstructed sample comprises the following steps: Based on the full-range equivalent stress-strain curve and the stress-strain curve of the weld material, and combined with the energy equivalence principle, the load P and elastic displacement h of the 0.5T-CT reconstructed sample are derived. e , elastic strain energy U e The relationship between: In the formula, represents the characteristic elastic strain energy, P e * represents the characteristic elastic load, P e * =k0EA * ; V * represents the characteristic volume, V * =A * h * ;h * A represents the characteristic displacement of the 0.5T-CT reconstructed sample; * It represents the characteristic area of ​​0.5T-CT reconstructed sample; P represents load; h e represents elastic displacement, U e represents elastic strain energy; The strain energy U is obtained from formula (1): e The relationship with load P is: Combined with the energy definition of J integral J We can get: Wherein, U represents the crack tip energy, B represents the thickness of the 0.5T-CT reconstructed specimen, a represents the crack length, P represents the load, k0 represents the coefficient to be determined, and E represents the elastic modulus of the material; the material includes the base material and / or the weld material; The elasticity J integral J e is equal to the energy G and can be obtained by converting the stress intensity factor K, the elastic J integral J e The relationship with the stress intensity factor K is: Where, E′ represents the equivalent elastic modulus of the material; J e represents elastic J integral J; K represents stress intensity factor G stands for energy; According to elastic J integral J e The relationship between stress intensity factor K and the calculation formula of stress intensity factor K is obtained: A finite element model of a 0.5T-CT reconstructed specimen is established, and an elastic finite element simulation analysis is performed on the 0.5T-CT reconstructed specimen to extract load and displacement, and the undetermined coefficient k0 of equations (3) and (5) is calibrated, thereby determining equations (3) and (5); The J integral J and the stress intensity factor K are obtained by performing calculations according to the determined formulas (3) and (5).

9. The testing method according to claim 7, characterized in that: J integral J includes pure plastic J integral J p ; Determine the pure plastic J integral J of the fracture parameters of the 0.5T-CT reconstructed specimen p The steps include: According to the energy equivalence principle, the load P, displacement h and pure plastic deformation energy U of the 0.5T-CT reconstructed specimen are derived. p The relationship between: Among them, the characteristic plastic strain energy U p * , characteristic load P p * , characteristic index m p Can be expressed as In the formula, k1 represents the first undetermined coefficient; k2 represents the second undetermined coefficient; k3 represents the third undetermined coefficient; k4 represents the fourth undetermined coefficient; the first undetermined coefficient, the second undetermined coefficient, the third undetermined coefficient and the fourth undetermined coefficient can be obtained by finite element analysis; K R represents the material coefficient; N represents the material index; V * Represents the characteristic volume of the sample, V * =h * A * ;h * represents the characteristic displacement of the specimen, A * Indicates the characteristic area of ​​the specimen; For the 0.5T-CT reconstructed sample, Where, W represents the width of the 0.5T-CT reconstructed specimen; B represents the thickness of the 0.5T-CT reconstructed specimen; a represents the crack length of the 0.5T-CT reconstructed specimen; m represents the effective volume reduction parameter related to the crack length of the 0.5T-CT reconstructed specimen; Substituting into equation (6) and equation (7), we can get the pure plastic deformation performance U p Relationship with load P Combined with the energy definition of J integral J The pure plastic J integral J of the 0.5T-CT restructured specimen can be obtained as p Calculation formula: During the pre-processing of the finite element software, the tensile mechanical parameters of the material are input, and the load-displacement curves under different a / W conditions are calculated. After geometrically independent processing (P / A*-h / h*), the parameter m can be obtained. Pure plastic calculation is performed on the original sample. According to formula (6), P under different stress hardening levels can be obtained. p *, m p , and then calibrate with formula (7) to obtain the first undetermined coefficient, the second undetermined coefficient, the third undetermined coefficient and the fourth undetermined coefficient, thereby determining formula (10); The pure plastic J integral J is calculated using the determined formula (10): p .

10. The testing method according to claim 7, characterized in that: The stress-strain relationship data of the weld material is obtained by the indentation method, and the full-range stress-strain data of the base material at different temperatures and the stress-strain relationship data of the weld material are input into the finite element model of the 0.5T-CT reconstructed specimen containing the weld to carry out calculations, thereby obtaining the load-displacement curve and the J integral J considering the material performance difference by finite element calculation; Analyze the J integral J of the fracture parameter and calculate J with the standard formula 标准试样 The proportional relationship between the integrals is used to calibrate the proportionality coefficient β of formula (11); Based on formula (11), the calculation formula of the J integral J of the fracture parameter can be obtained, and then the J integral J of the fracture parameter can be obtained; In the formula, J represents the J integral of the crack tip of the 0.5T-CT reconstructed specimen, J, 标准试样 represents the crack tip J integral J calculated by the standard formula of the parent material; β represents the proportionality coefficient, F represents the loading load, B represents the thickness of the 0.5T-CT reconstructed specimen, and B N represents the net thickness of the 0.5T-CT reconstructed specimen, a represents the crack length of the 0.5T-CT reconstructed specimen, W represents the crack width of the 0.5T-CT reconstructed specimen, E represents the equivalent elastic modulus, v represents the Poisson's ratio, η p represents the plasticity factor, U p represents the plastic deformation energy of the 0.5T-CT reconstructed specimen after loading, and a0 represents the initial crack length of the 0.5T-CT reconstructed specimen.