Method and system for testing fracture toughness of large-diameter thin-walled metal tube

Abstract

The present application belongs to the technical field of metal material fracture performance test, and provides a large-diameter metal thin-walled pipe fracture toughness test method and system. In the present application, the load-displacement curve of the crack curved surface sample of the large-diameter metal thin-walled pipe, and the initial crack length and the terminal crack length of the crack curved surface sample section are obtained. First, the real-time crack length and the crack propagation amount Δa are directly obtained by the regularization method. Then, the J integral value of the crack curved surface sample is calculated according to the obtained real-time crack length and the load, and the J integral expression. Finally, the J-Δa resistance curve is obtained according to the crack propagation amount Δa and the J integral value. The data processing process is simple, and the fracture toughness of the material can be obtained only by simply processing the sample load-displacement curve obtained by the experiment.

Description

Technical Field

[0001] This invention belongs to the field of fracture performance testing technology for metallic materials, and particularly relates to a method and system for testing the fracture toughness of large-diameter thin-walled metal tubes. Background Technology

[0002] Fracture toughness is a crucial mechanical property parameter for evaluating a structural member's resistance to fracture failure. Especially when metallic materials need to withstand internal high temperatures and pressures (such as in high-pressure pipelines), selecting engineering materials with high fracture toughness is essential for ensuring structural reliability. Therefore, obtaining the fracture toughness of materials through reliable testing methods is vital in the safety assessment of engineering components.

[0003] On the other hand, in the design of structural components such as high-pressure pipelines, under the same pipe diameter specifications, the lower the pipe wall thickness can be if a higher-strength metal material is used. For example, the pressure tubes used in the core area of ​​heavy water reactors are made of a special Zr-2.5Nb alloy, containing the high-temperature (approximately 300°C) and high-pressure (approximately 12MPa) core coolant. This alloy has a strength far exceeding that of other nuclear-grade zirconium alloys and stainless steel, thus requiring a thickness of only about 4mm. However, because large-diameter, thin-walled metal tubes have a typically curved structure, it is impossible to cut standard compact tensile (CT) or single-edged bending (SEB) specimens for fracture toughness testing. This limitation hinders the application of new high-strength metal materials.

[0004] The inventors discovered that, in order to study the fracture performance of large-diameter thin-walled metal tubes containing axial and circumferential cracks, existing technologies, based on the structural characteristics of pressure tubes, have designed... Figure 1 The CT specimens with axial and circumferential cracks shown were used for fracture toughness testing of pressure tubes, but they still employ a test method applicable only to standard CT specimens, which will inevitably lead to significant differences in the test results. There is currently no effective fracture toughness testing method for CT specimens with axial and circumferential cracks. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method and system for testing the fracture toughness of large-diameter thin-walled metal tubes. This invention presents a J-integral formula for CT specimens with axial cracks on curved surfaces, overcoming the shortcomings of current methods that do not consider the influence of curved surface structures. The experimental principle and data processing are simple; the fracture toughness of the material can be obtained simply by performing basic data processing on the load-displacement curves of the specimens obtained from the experiment.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for testing the fracture toughness of large-diameter thin-walled metal tubes, comprising:

[0008] Obtain the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the final crack length of the cross section of the cracked surface specimen.

[0009] Based on the regularization method, and the obtained load-displacement curve, initial crack length, and terminal crack length, the real-time crack length is obtained;

[0010] Based on the obtained real-time crack length and the test time, the crack propagation amount Δa is calculated.

[0011] Based on the obtained real-time crack length and load, as well as the J integral expression, the J integral value of the cracked surface specimen is calculated.

[0012] Based on the crack propagation amount Δa and the integral value of J, the J-Δa resistance curve is obtained.

[0013] Furthermore, the loads at each point from the starting point of the load-displacement curve to the maximum load are normalized. The load at each point after normalization is equal to the normalized load value at each point before normalization. The normalized value is equal to the product of the reference yield stress, the specimen width, and the specimen thickness, multiplied by 1 minus the product of the m-th power of the difference between the passivation correction crack length and the specimen width ratio; where m is a parameter to be determined.

[0014] Furthermore, the passivated crack length is equal to the sum of the initial crack length plus the ratio of the integral value of J to the product of the tensile strength of the specimen and the set constant.

[0015] Furthermore, the displacement at each point on the load-displacement curve is normalized; the displacement at each point after normalization is equal to the difference between the product of the load and the elastic compliance at each point before normalization and the quotient of the sample width.

[0016] Furthermore, at the end of the experiment, the obtained load-displacement is normalized using the length of the termination crack; a tangent is drawn from the normalized test point obtained through the termination crack to the preceding data points, and the data points to the left of the tangent point and whose normalized displacement is greater than the preset value and the termination crack point are used as the fitting of the normalization function; the normalization function is equal to the sum of the first fitting parameter, the product of the second fitting parameter and the normalized displacement, and the product of the third fitting parameter and the square of the normalized displacement, and then divided by the quotient of the sum of the fourth fitting parameter and the normalized displacement.

[0017] Furthermore, the integral expression for J is:

[0018]

[0019] Where ν is Poisson's ratio; K is the stress intensity coefficient of the material; E is the elastic modulus; a is the crack length; m, k1, and k2 are all parameters to be determined; W is the specimen width; N is the stress hardening index; and P is the load. Where, m p These are parameters to be determined.

[0020] Secondly, the present invention also provides a method for testing the fracture toughness of large-diameter thin-walled metal tubes, comprising:

[0021] Fatigue loading under load control was performed on cracked surface specimens of large-diameter thin-walled metal tubes to pre-fabricate the cracks in the specimens; fracture toughness tests were conducted on the cracked surface specimens with displacement control to obtain the load-displacement curves of the specimens; the lengths of the initial crack and the final crack were measured from the cross-section of the cracked surface specimens.

[0022] Based on the regularization method, and the obtained load-displacement curve, initial crack length, and terminal crack length, the real-time crack length is obtained;

[0023] Based on the obtained real-time crack length and the test time, the crack propagation amount Δa is calculated.

[0024] Based on the obtained real-time crack length and load, as well as the J integral expression, the J integral value of the cracked surface specimen is calculated.

[0025] Based on the crack propagation amount Δa and the integral value of J, the J-Δa resistance curve is obtained.

[0026] Thirdly, the present invention also provides a fracture toughness testing system for large-diameter thin-walled metal tubes, comprising:

[0027] The data acquisition module is configured to acquire the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the termination crack length of the cross section of the cracked surface specimen.

[0028] The regularization module is configured to obtain the real-time crack length based on the regularization method and the obtained load-displacement curve, initial crack length, and termination crack length.

[0029] The crack propagation calculation module is configured to calculate the crack propagation Δa based on the obtained real-time crack length and the test time.

[0030] The J-integral module is configured to calculate the J-integral value of the cracked surface specimen based on the obtained real-time crack length and load, as well as the J-integral expression.

[0031] The resistance curve plotting module is configured to obtain the J-Δa resistance curve based on the crack propagation amount Δa and the J integral value.

[0032] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the fracture toughness test method for large-diameter thin-walled metal tubes described in the first aspect.

[0033] Fifthly, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the fracture toughness test method for large-diameter thin-walled metal tubes described in the first aspect.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. This invention proposes a J-integral formula for CT specimens with axial and circumferential cracked surfaces, which overcomes the shortcomings of current methods that do not consider the influence of the specimen surface structure. Through a simple experimental principle and data processing, the fracture toughness of large-diameter thin-walled metal pipes can be measured.

[0036] 2. In this invention, based on obtaining the load-displacement curve of a cracked surface specimen of a large-diameter thin-walled metal tube, and the initial crack length and termination crack length of the cross-section of the cracked surface specimen, the real-time crack length and crack propagation Δa are first directly obtained through a regularization method; then, based on the obtained real-time crack length and load, and the J integral expression, the J integral value of the cracked surface specimen is calculated; finally, based on the crack propagation Δa and the J integral value, the J-Δa resistance curve is obtained; the data processing process is simple, requiring only simple data processing of the experimentally obtained load-displacement curve of the specimen to obtain the fracture toughness of the material.

[0037] 3. The method of this invention has a solid theoretical basis and low experimental cost. If the sample size changes, there is no need to recalibrate the parameters. The crack length can be obtained by combining the regularization method. The J integral value can be obtained by simply combining the load and the real-time crack length, and then the J resistance curve of the material can be obtained, which is convenient for popularization and application. Attached Figure Description

[0038] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0039] Figure 1 The cracked surface CT sample of Embodiment 1 of the present invention;

[0040] Figure 2(a) is a plan view of the CT specimen with axial crack in the curved surface of Embodiment 1 of the present invention;

[0041] Figure 2(b) is a plan view of the CT specimen with circumferential cracks on the curved surface in Embodiment 2 of the present invention;

[0042] Figure 3 This is a schematic diagram of the cracked surface CT sample structure of Embodiment 1 of the present invention;

[0043] Figure 4 This is a schematic diagram of the loading of a cracked curved surface CT sample according to Embodiment 1 of the present invention;

[0044] Figure 5 This is a schematic diagram of the regularization method in Embodiment 1 of the present invention;

[0045] Figure 6 The Ph curve is from Embodiment 1 of the present invention;

[0046] Figure 7 The J-resistance curve is shown in Embodiment 1 of the present invention;

[0047] Figure 8 The crack front J-integral nonlinear distribution is shown in Embodiment 2 of the present invention.

[0048] Figure 9 This is the non-uniform crack propagation morphology of the sample cross-section in Example 2 of the present invention;

[0049] Figure 10 This is a schematic diagram of the regularization method in Embodiment 2 of the present invention;

[0050] Figure 11 This is the Ph curve of Embodiment 2 of the present invention;

[0051] Figure 12 This is the J-resistance curve of Embodiment 2 of the present invention. Detailed implementation method:

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0053] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0054] Example 1:

[0055] This embodiment provides a method for testing the fracture toughness of large-diameter thin-walled metal tubes, including:

[0056] Obtain the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the final crack length of the cross section of the cracked surface specimen.

[0057] Based on the regularization method, and the obtained load-displacement curve, initial crack length, and terminal crack length, the real-time crack length is obtained;

[0058] Based on the obtained real-time crack length and the test time, the crack propagation amount Δa is calculated.

[0059] Based on the obtained real-time crack length and load, as well as the J integral expression, the J integral value of the cracked surface specimen is calculated.

[0060] Based on the crack propagation amount Δa and the integral value of J, the J-Δa resistance curve is obtained.

[0061] Specifically, the large-diameter thin-walled metal tube in this embodiment can be a heavy water reactor pressure tube or other pipes with a large diameter; this embodiment includes four parts: a CT sample with axial cracks and a loading device, J-integral calculation, a real-time crack length acquisition method, and a test method.

[0062] The axial crack curved surface CT specimen and loading device used in this embodiment are shown in Figure 2(a). The specimen thickness B is taken as the actual thickness of the pipe. The ratio of specimen width W to specimen thickness B is W / B = 4-5. The ratio of crack length a to specimen width W is a / W = 0.4-0.7. The notch width D should be designed to match the gauge length of the displacement measurement sensor. The crack width h should not exceed 2mm, and the crack root should be sufficiently sharp. Typically, machining combined with pre-induced fatigue cracks is used to achieve this. Figure 3 As shown, the axially cracked curved surface CT specimen is connected to the U-shaped clamp by two pins to achieve tensile loading, and the U-shaped clamp is rigidly connected to the testing machine clamp.

[0063] The J integral formula uses the RO constitutive relation model shown in equation (1) to describe the stress-strain relationship of the material:

[0064]

[0065] Where ε and σ are the true strain and true stress of the material, respectively; ε e and ε p These represent elastic strain and plastic strain, respectively; E is the elastic modulus; K is the stress intensity coefficient of the material; and N is the stress hardening index.

[0066] The elastic displacement h is obtained using the energy density equivalent method. e The relationship with load P is as follows:

[0067]

[0068] Where W is the width of the specimen; a is the crack length of the specimen; B is the thickness of the specimen; E is the elastic modulus; and p0~p3 are parameters to be determined. From equation (2), the K-factor expression for the CT specimen with an axial crack can be obtained:

[0069]

[0070] The plastic displacement h was obtained using the energy density equivalent method. p The relationship with load P is as follows:

[0071]

[0072] Where m, m p k1 and k2 are both undetermined parameters. From equation (4) and combined with equation (3), the integral expression for J of the CT specimen with an axial crack surface can be obtained:

[0073]

[0074] In the formula, ν is Poisson's ratio. The parameters in equations (3) and (5) were calibrated by finite element analysis, and the results are shown in Table 1.

[0075] Table 1 Calibration parameter values

[0076] m <![CDATA[k1]]> <![CDATA[k2]]> <![CDATA[p0]]> <![CDATA[p1]]> <![CDATA[p2]]> <![CDATA[p3]]> 2.0800 1.1383 0.3960 0.1573 -0.4369 0.4386 -0.1595

[0077] The real-time crack length acquisition method, the regularization method, can directly obtain the initial crack length a0 and the final crack length a0 from the load-displacement curve of the CT specimen with an axial crack and the cross-section of the CT specimen with an axial crack measured by opening it. f The real-time crack length is then obtained.

[0078] Assume the load P of a CT specimen with an axial crack can be expressed as the product of two independent geometric functions g(a / W) and deformation function f(h / W):

[0079]

[0080] The load P at each point from the starting point of the load-displacement curve to the point before the maximum load. i Rule-based processing:

[0081]

[0082] σ0 is the reference yield stress, a bi Crack length for passivation correction:

[0083]

[0084] Among them, R m J is the tensile strength of the specimen. ia0 can be substituted into equation (5) to obtain the result.

[0085] Regularize the displacement at each point on the load-displacement curve:

[0086]

[0087] Among them, C i It refers to elastic flexibility.

[0088] At the end of the test, the obtained load-displacement ratio was taken as the termination crack length a. f Substituting equations (7) and (8) into the regularization process, the fitting diagram is shown below. Figure 4 As shown. Draw a tangent line from the regularized test point obtained through the terminated crack to the preceding data point, and mark the left side of the tangent point (including the tangent point) and h pi Data points with a W value greater than 0.001 and the termination crack point were used as the regularization function for fitting.

[0089]

[0090] In the formula, c1-c4 are the fitting coefficients.

[0091] The crack length a can be solved using equations (7) and (10). i until P N The difference from the experimental measurement was within ±0.1%, and each subsequent data point was processed using a similar method.

[0092] The load and crack length at each test point can be obtained by the above method. Then, the J corresponding to each point can be calculated by equation (5), and the J-Δa resistance curve can be obtained.

[0093] Example 2:

[0094] This embodiment provides a method for testing the fracture toughness of large-diameter thin-walled metal tubes, including:

[0095] Obtain the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the final crack length of the cross section of the cracked surface specimen.

[0096] Based on the regularization method, and the obtained load-displacement curve, initial crack length, and terminal crack length, the real-time crack length is obtained;

[0097] Based on the obtained real-time crack length and the test time, the crack propagation amount Δa is calculated.

[0098] Based on the obtained real-time crack length and load, as well as the J integral expression, the J integral value of the cracked surface specimen is calculated.

[0099] Based on the crack propagation amount Δa and the integral value of J, the J-Δa resistance curve is obtained.

[0100] Specifically, this embodiment includes four parts: a CT sample with a circumferential crack and a loading device, J-integral calculation, a method for obtaining real-time crack length, and a test method.

[0101] The circumferential crack surface CT specimen and loading device used in the technical solution of this invention are shown in Figure 2(b). The specimen thickness B is taken as the actual thickness of the pipe; the ratio of specimen width W to specimen thickness B, W / B = 4-5; the ratio of crack length a to specimen width W, a / W = 0.4-0.7; the notch width D should be designed to match the gauge length of the displacement measurement sensor; the crack width h should not exceed 2mm, and the crack root should be sufficiently sharp, typically achieved through machining combined with pre-induced fatigue cracks. Figure 3 As shown, the CT specimen with circumferential crack is connected to the U-shaped clamp by two pins to achieve tensile loading, and the U-shaped clamp is rigidly connected to the chuck of the testing machine.

[0102] The J integral formula uses the RO constitutive relation model shown in equation (11) to describe the stress-strain relationship of the material:

[0103]

[0104] Where ε and σ represent the true strain and true stress of the material, respectively. e and ε p Let E represent elastic strain and plastic strain respectively, E represent the elastic modulus, K represent the stress intensity coefficient of the material, and N represent the stress hardening index.

[0105] The elastic displacement h is obtained using the energy density equivalent method. e The relationship with load P is expressed in equation (12).

[0106]

[0107] Where W represents the width of the specimen, a represents the crack length of the specimen, B represents the thickness of the specimen, E is the elastic modulus, and p0~p3 are parameters to be determined. From equation (12), the expression for the K-factor of the CT specimen with a circumferential crack can be obtained:

[0108]

[0109] The plastic displacement h was obtained using the energy density equivalent method. p The relationship with load P is expressed as equation (14).

[0110]

[0111] Where m, k1, and k2 are all undetermined parameters. From equation (14) and combined with equation (13), the integral expression for J of the CT specimen with a circumferential crack surface can be obtained:

[0112]

[0113] In the formula, ν is Poisson's ratio. The parameters in equations (13) and (15) were calibrated by finite element analysis, and the results are shown in Table 2.

[0114] Table 2 Calibration Parameter Values

[0115] m <![CDATA[k1]]> <![CDATA[k2]]> <![CDATA[p0]]> <![CDATA[p1]]> <![CDATA[p2]]> <![CDATA[p3]]> 2.105 1.066 0.4529 0.1760 -0.5397 0.6063 -0.2527

[0116] Due to the nonlinear propagation path of the CT specimen containing a circumferential crack, the J-integral at the crack front exhibits a non-uniform distribution characteristic, such as... Figure 8 As shown, this leads to the following during the specimen fracture test: Figure 9 The non-uniform crack propagation is shown. The J-integral at a local location with arbitrary thickness is J... i It can be represented as:

[0117]

[0118] Where z is the local coordinate of the sample thickness, J w The weighted average of the J integrals at different thickness locations at the crack front of the specimen is calculated by equation (15). Equation (16) can be used to calculate the J integral at the local thickness of interest at the crack front of the CT specimen containing a circumferential crack, as needed.

[0119] The real-time crack length acquisition method, the regularization method, can directly obtain the initial crack length a0 and the final crack length a0 from the load-displacement curve of the CT specimen with a circumferential crack and the cross-section of the CT specimen with a circumferential crack measured by opening the cross-section. f The real-time crack length is then obtained. Assume the load P on the CT specimen with the circumferential crack can be expressed as the product of two independent geometric functions g(a / W) and deformation function f(h / W):

[0120]

[0121] The load P at each point from the starting point of the load-displacement curve to the point before the maximum load. i Rule-based processing:

[0122]

[0123] σ0 is the reference yield stress, a bi Crack length for passivation correction:

[0124]

[0125] In the formula R m J is the tensile strength of the specimen. i a0 can be substituted into equation (16) to obtain the result.

[0126] Regularize the displacement at each point on the load-displacement curve:

[0127]

[0128] Among them, C i It refers to elastic flexibility.

[0129] At the end of the test, the obtained load-displacement ratio was taken as the termination crack length a. f Substituting equations (18) and (19) into the regularization process, the fitting diagram is shown below. Figure 10 As shown. Draw a tangent line from the regularized test point obtained through the terminated crack to the preceding data point, and mark the left side of the tangent point (including the tangent point) and h pi Data points with a W value greater than 0.001 and the point where the crack terminates are used for fitting the regularization function:

[0130]

[0131] Where c1-c4 are the fitting coefficients.

[0132] The crack length a can be solved using equations (18) and (21). i until P N The difference from the experimental measurement was within ±0.1%, and each subsequent data point was processed using a similar method.

[0133] The load and crack length at each test point can be obtained by the above method. Then, the J corresponding to each point can be calculated by equation (16), and the J-Δa resistance curve can be obtained.

[0134] Example 3:

[0135] This embodiment provides a method for testing the fracture toughness of large-diameter thin-walled metal tubes, including:

[0136] S1. Preparation of specimens and testing fixtures: Machining CT specimens with axial or circumferential cracks. The specimen configuration is shown in Figure 2(a) or Figure 2(b). The U-shaped fixture is as follows: Figure 3 As shown.

[0137] S2. The test procedure is as follows: First, the CT specimen with axial or circumferential cracks and a U-shaped fixture are mounted on the testing machine. Fatigue loading is applied to the specimen under controlled load to pre-fatigue the cracks. Second, after the fatigue crack pre-crease is complete, the CT specimen with axial cracks is subjected to fracture toughness testing under displacement control to obtain the load-displacement curve. Third, the crack front at different propagation stages is delineated using secondary fatigue or thermal coloring methods. Finally, the specimen is opened, and the lengths of the pre-creased initial and terminated cracks are measured from the specimen cross-section.

[0138] The S3 and J resistance curves are obtained by using the regularization method to obtain the real-time crack length a of the sample, and then determining the crack propagation amount Δa. The crack propagation amount Δa can be understood as the crack propagation rate, which is the amount of crack propagation per unit time. The real-time crack length and load are substituted into formula (5) in Example 1 to calculate the J integral of the sample, and then the J-Δa resistance curve is obtained.

[0139] The method for calculating the fracture toughness parameters in the fracture toughness test method for large-diameter thin-walled metal tubes is the same as that in Example 1 or Example 2, and will not be repeated here.

[0140] Example 4:

[0141] This embodiment provides a fracture toughness testing system for large-diameter thin-walled metal tubes, including:

[0142] The data acquisition module is configured to acquire the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the termination crack length of the cross section of the cracked surface specimen.

[0143] The regularization module is configured to obtain the real-time crack length based on the regularization method and the obtained load-displacement curve, initial crack length, and termination crack length.

[0144] The crack propagation calculation module is configured to calculate the crack propagation Δa based on the obtained real-time crack length and the test time.

[0145] The J-integral module is configured to calculate the J-integral value of the cracked surface specimen based on the obtained real-time crack length and load, as well as the J-integral expression.

[0146] The resistance curve plotting module is configured to obtain the J-Δa resistance curve based on the crack propagation amount Δa and the J integral value.

[0147] The working method of the system is the same as that of the fracture toughness test method for large-diameter thin-walled metal tubes in Example 1, and will not be repeated here.

[0148] Example 5:

[0149] This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the fracture toughness test method for large-diameter thin-walled metal tubes described in Embodiment 1.

[0150] Example 6:

[0151] This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps of the fracture toughness test method for large-diameter thin-walled metal tubes described in Embodiment 1.

[0152] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A test method for fracture toughness of large-diameter thin-walled metal tubes, characterized in that, include: Obtain the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the final crack length of the cross section of the cracked surface specimen. Based on the regularization method, and the obtained load-displacement curve, initial crack length, and terminal crack length, the real-time crack length is obtained; Based on the obtained real-time crack length and the test time, the crack propagation amount Δ is calculated. a ; Based on the obtained real-time crack length and load, and J The integral expression is used to calculate the cracked surface specimen. J Integral value; Based on the crack propagation amount Δ a and stated J The integral value is obtained. J- Δ a Resistance curve; J The integral expression is: in, ν Poisson's ratio; K The stress intensity coefficient of the material; E It is the elastic modulus; The length of the crack; m , k 1 and k Both are parameters to be determined; W The width of the sample; N It is the stress hardening index; P For load; ,in, These are parameters to be determined. The thickness is the sample thickness.

2. The method for testing the fracture toughness of large-diameter thin-walled metal tubes as described in claim 1, characterized in that, The loads at each point from the starting point of the load-displacement curve to the maximum load are normalized. The load at each point after normalization is equal to the normalized load value at each point before normalization. The normalized value is equal to the product of the reference yield stress, the specimen width, and the specimen thickness, multiplied by 1 and then subtracted from the difference between the passivation correction crack length and the specimen width ratio. m The product of powers; where m These are parameters to be determined.

3. The method for testing the fracture toughness of large-diameter thin-walled metal tubes as described in claim 2, characterized in that, The passivated crack length is equal to the initial crack length plus... J The sum of the integral value and the ratio of the product of the tensile strength of the sample and the set constant.

4. The method for testing the fracture toughness of large-diameter thin-walled metal tubes as described in claim 1, characterized in that, The displacement at each point on the load-displacement curve is normalized. The displacement at each point after normalization is equal to the displacement at each point before normalization minus the difference between the product of the load and the elastic compliance at each point before normalization, and then divided by the quotient of the sample width.

5. The method for testing the fracture toughness of large-diameter thin-walled metal tubes as described in claim 1, characterized in that, At the end of the test, the obtained load-displacement is normalized using the length of the termination crack. A tangent is drawn from the normalized test point obtained through the termination crack to the preceding data points. The data points to the left of the tangent point and whose normalized displacement is greater than the preset value, along with the termination crack point, are used as the fitting points for the normalization function. The normalization function is equal to the sum of the first fitting parameter, the product of the second fitting parameter and the normalized displacement, and the product of the third fitting parameter and the square of the normalized displacement, divided by the quotient of the sum of the fourth fitting parameter and the normalized displacement.

6. A test method for fracture toughness of large-diameter thin-walled metal tubes, characterized in that, include: Fatigue loading under load control was performed on cracked surface specimens of large-diameter thin-walled metal tubes to pre-fabricate the cracks in the specimens; fracture toughness tests were conducted on the cracked surface specimens with displacement control to obtain the load-displacement curves of the specimens; the lengths of the initial crack and the final crack were measured from the cross-section of the cracked surface specimens. Based on the regularization method, and the obtained load-displacement curve, initial crack length, and terminal crack length, the real-time crack length is obtained; Based on the obtained real-time crack length and the test time, the crack propagation amount Δ is calculated. a ; Based on the obtained real-time crack length and load, and J The integral expression is used to calculate the cracked surface specimen. J Integral value; Based on the crack propagation amount Δ a and stated J The integral value is obtained. J- Δ a Resistance curve; J The integral expression is: in, ν Poisson's ratio; K The stress intensity coefficient of the material; E It is the elastic modulus; The length of the crack; m , k 1 and k Both are parameters to be determined; W The width of the sample; N It is the stress hardening index; P For load; ,in, These are parameters to be determined. The thickness is the sample thickness.

7. A fracture toughness testing system for large-diameter thin-walled metal tubes, characterized in that, include: The data acquisition module is configured to acquire the load-displacement curve of the cracked surface specimen of a large-diameter thin-walled metal tube, as well as the initial crack length and the termination crack length of the cross section of the cracked surface specimen. The regularization module is configured to obtain the real-time crack length based on the regularization method and the obtained load-displacement curve, initial crack length, and termination crack length. The crack propagation calculation module is configured to calculate the crack propagation amount Δ based on the obtained real-time crack length and the test time. a ; J The integration module is configured to: based on the obtained real-time crack length and load, and J The integral expression is used to calculate the cracked surface specimen. J Integral value; The resistance curve plotting module is configured to: based on the crack propagation amount Δ a and stated J The integral value is obtained. J- Δ a Resistance curve; J The integral expression is: in, ν Poisson's ratio; K The stress intensity coefficient of the material; E It is the elastic modulus; The length of the crack; m , k 1 and k Both are parameters to be determined; W The width of the sample; N It is the stress hardening index; P For load; ,in, These are parameters to be determined. The thickness is the sample thickness.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program implements the steps of the fracture toughness test method for large-diameter thin-walled metal tubes as described in any one of claims 1-5.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the fracture toughness test method for large-diameter thin-walled metal tubes as described in any one of claims 1-5.

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