Prediction method for fracture toughness of polar region marine composite steel plate under different thicknesses

Abstract

The invention relates to the technical field of metal material fracture resistance testing, in particular to a prediction method for fracture toughness of a polar region ship composite steel plate under different thicknesses, and the method comprises the following specific steps: S1, material selection and performance testing; s2, carrying out a fracture test; s3, modeling and simulation: performing modeling on the composite steel plate samples with different composite layer thicknesses, and performing fracture behavior simulation; s4, model establishment and parameter fitting; and S5, model verification and application. According to the method, the layer thickness ratio Rt is used as a key research parameter, the fracture toughness change rule of the polar ship composite steel plate under different composite layer thicknesses can be systematically represented, and the fracture toughness prediction model based on the layer thickness ratio is established, so that the problems of complexity and high cost caused by one-by-one test on all the composite layer thicknesses in a traditional method are effectively solved; therefore, the actual engineering requirements of rapid fracture resistance design and economic evaluation of the polar ship composite steel plate are met, the test quantity is small, the period is short, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of anti-fracture performance testing of metal materials, and particularly relates to a method for predicting the fracture toughness of polar marine composite steel plates at different thicknesses. Background Art

[0002] In recent years, the rich resources contained in the polar regions and the gradual opening of the Arctic shipping lanes have greatly highlighted the strategic position of the Arctic. As an important platform for polar region development and scientific research, polar ships, especially icebreakers, have an urgent need for high-performance materials. The icebreaking parts of advanced icebreakers all use anti-corrosion and wear-resistant composite steel plates. However, composite steel plates are mostly produced by explosion or rolling methods, and defects such as pores and slag inclusions are likely to occur at the interface due to severe plastic deformation during the composite process. During the service process of composite steel plates, they need to withstand the extrusion and impact of ice layers for a long time, and cracks are likely to initiate at the interface defects. Once the crack extends vertically to the base layer at the interface, there is a risk of brittle fracture at low polar temperatures. To ensure structural safety, when there are cracks under the cladding layer, it is necessary to conduct experimental research on the fracture toughness of composite steel plates.

[0003] In the actual application process, considering the principle of economy, the required cladding layer thickness of composite steel plates varies according to different service conditions. However, the current influence mechanism of cladding layer thickness on the fracture toughness of composite steel plates is not clear. According to the conventional method, to study the fracture toughness of composite steel plate specimens at different cladding layer thicknesses, it is first necessary to produce composite steel plates at all cladding layer thicknesses, and then sample and test them one by one. The amount of testing is large, the cycle is long, and the cost is high.

[0004] Publication No.: CN119064180A, a method for testing the fracture toughness of fiber-reinforced ceramic matrix composites, realizes the in-situ observation of the whole process of crack initiation and propagation of ceramic matrix composites under external loads through in-situ mechanical testing technology, providing microscopic experimental data for the testing of fracture toughness; then combines the in-situ test with finite element simulation, introducing the influence of microscopic structure and interlayer transverse cracking behavior on the overall fracture toughness of ceramic matrix composites, and improving the effectiveness and rationality of fracture toughness prediction. However, this solution involves high-precision microscopic observation equipment and special test fixtures, increasing the complexity and cost of the test. Moreover, due to the need for in-situ mechanical testing and complex finite element simulation, the fracture toughness test period of fiber-reinforced ceramic matrix composites may be long and the efficiency is low.

[0005] Therefore, there is an urgent need to design a new method for predicting fracture toughness to solve the problems of large amount of testing, long cycle, and high cost existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention aims to propose a method for predicting the fracture toughness of polar marine composite steel plates with different thicknesses, so as to solve the problems of large test quantity, long cycle, and high cost existing in the prior art.

[0007] To solve this problem, the present invention creatively proposes a prediction model for the fracture toughness of polar marine composite steel plates with different clad layer thicknesses, which can achieve rapid prediction and evaluation, and provide technical support for the anti-fracture design of composite steel plates. The present invention takes the layer thickness ratio as the research parameter and defines the layer thickness ratio R t as the ratio of the clad layer thickness t1 to the base layer thickness t2, that is, R t = t1 / t2. By obtaining basic data through fracture tests at specific clad layer thicknesses and using finite element simulation technology, a model analysis is carried out on composite steel plates with different clad layer thicknesses to simulate the fracture behavior. Based on the fracture test and finite element simulation results, a fracture toughness prediction model characterized by the layer thickness ratio is established, which can realize the rapid prediction and evaluation of the fracture toughness of composite steel plates.

[0008] The technical solution of the present invention is realized as follows:

[0009] The present invention discloses a method for predicting the fracture toughness of polar marine composite steel plates with different thicknesses, including the following specific steps:

[0010] S1: Material selection and property testing: Select the base layer and clad layer materials, conduct tensile tests on the materials according to the standards, and obtain the property data of the base layer and clad layer materials;

[0011] S2: Fracture test: Prepare specimens according to the requirements, perform notch machining, conduct fracture tests on the specimens, and obtain the fracture loads when the crack penetrates the clad layer and when the clad layer is intact;

[0012] S3: Modeling and simulation: Model the composite steel plate specimens with different clad layer thicknesses, set the material properties, boundary conditions, and loading methods, conduct fracture behavior simulation, extract the load-displacement curves during the simulation process, and analyze the fracture behavior;

[0013] S4: Model establishment and parameter fitting: Based on the fracture test and simulation results, establish a fracture toughness prediction model and fit the undetermined parameters in the model;

[0014] S5: Model verification and application: Compare the calculated fracture toughness values obtained from the prediction model with the measured values to verify the accuracy of the model, and apply the prediction model to predict the fracture toughness of composite steel plates with different clad layer thicknesses to provide a basis for anti-fracture design.

[0015] Furthermore, in step S1, the base layer material is FH40, and the clad layer material is 317L stainless steel.

[0016] Further, in step S1, a tensile test is performed on the clad steel plate in accordance with GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", and the obtained data are material density, yield strength, tensile strength, elastic modulus, Poisson's ratio, plastic parameters, and Maxpe damage criterion parameters.

[0017] Further, in step S2, a sample is taken from the clad steel plate, a notch is machined according to the drawing, and a three-point bending fracture test is carried out in accordance with the requirements of GB-T21143-2014 "Unified test method for quasi-static fracture toughness of metallic materials", with a loading span S, and the fracture load when the crack penetrates the clad layer and the clad layer is intact is obtained.

[0018] Further, in step S2, the total crack length is taken as 13 mm, the specimen width is W, and the span S = 4W.

[0019] Further, in step S3, finite element software is used to model the clad steel plate specimens with different clad layer thicknesses.

[0020] Further, in step S3, the finite element model keeps the total size and the total crack length unchanged, only changes the layer thickness ratio, the clad layer thickness is taken at intervals of 1 mm, where the interface is simplified to a bonded contact, and the rest are sliding friction contacts; the model mesh element type is an eight-node linear hexahedron element (C3SD8R), and the mesh division strategy is dense in the middle and sparse at both ends.

[0021] Further, in step S3, the calculation and simulation process is carried out using the extended finite element method (XFEM) embedded in ABAQUS, a quasi-static analysis step is adopted, crack propagation is allowed, and the failure criterion is the Maxpe damage criterion.

[0022] Further, in step S4, the specific form of the fracture toughness prediction model is:

[0023] ................................................(1)

[0024] ................................(2);

[0025] where: t1 is the clad layer thickness;

[0026] t2 is the base layer thickness;

[0027] R t is the layer thickness ratio;

[0028] S is the specimen span;

[0029] W is the specimen width;

[0030] B is the specimen height;

[0031] a0 is the crack length;

[0032] Obtained through Appendix B of GB-T 21143-2014 "Unified Test Method for Quasi-Static Fracture Toughness of Metallic Materials";

[0033] A1, A2, X0, and p are undetermined parameters.

[0034] Furthermore, in step S4, the undetermined parameters in the model are fitted using the least squares method.

[0035] Compared with the prior art, the method for predicting the fracture toughness of a polar marine composite steel plate at different thicknesses of the present invention has the following advantages:

[0036] 1. By taking the layer thickness ratio R t as the key research parameter, the present invention can systematically characterize the variation law of the fracture toughness of polar marine composite steel plates at different cladding layer thicknesses, and establish a fracture toughness prediction model based on the layer thickness ratio, effectively solving the cumbersome and high-cost problems of the traditional method that requires one-by-one tests for all cladding layer thicknesses, thus meeting the engineering actual needs of rapid anti-fracture design and economic evaluation of polar ship composite steel plates, with small test volume, short cycle, and low cost.

[0037] 2. The method of the present invention combines fracture tests and finite element simulation technology, with a simple and clear construction process, strong operability, facilitating rapid implementation of tests and data analysis in actual engineering. The obtained prediction model can accurately reflect the fracture toughness characteristics of composite steel plates at different cladding layer thicknesses, providing a scientific basis and technical support for the optimization of the anti-fracture performance of polar ship composite steel plates.

[0038] 3. The present invention can quickly predict the fracture toughness of composite steel plates at different cladding layer thicknesses through finite element simulation and a small amount of key test data, significantly improving the research efficiency, reducing the test cost, with accurate and reliable prediction results, which can be directly applied to the damage tolerance design and safety assessment of polar ship composite steel plates, providing an important guarantee for improving the safety and reliability of polar ships. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0040] Figure 1 is a schematic diagram of the composite steel plate;

[0041] Figure 2It is a schematic diagram of a three-point bending test;

[0042] Figure 3 It is a schematic diagram of the specimen when the crack penetrates the clad layer in Example 1;

[0043] Figure 4 It is a schematic diagram of the specimen when the clad layer is intact and the clad layer is at its maximum value in Example 1;

[0044] Figure 5 It is a finite element model;

[0045] Figure 6 It is the finite element model after meshing;

[0046] Figure 7 It is the load-displacement curves at different clad layer thicknesses;

[0047] Figure 8 It is the numerical calculation results and the model prediction results.

[0048] Reference numerals:

[0049] 1, base layer; 2, clad layer; 3, loading roller; 4, support roller. Detailed implementation manners

[0050] In order to make the technical means, achieved purposes and effects of the present invention easy to understand, the embodiments of the present invention will be described in detail below with reference to specific drawings.

[0051] It should be noted that all the terms indicating directions and positions in the present invention, such as: "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "inner", "outer", "top", "bottom", "lateral", "longitudinal", "center", etc., are only used to explain the relative positional relationship and connection situation between components in a certain specific state, and are only for the convenience of describing the present invention, rather than requiring the present invention to be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the descriptions involving "first", "second", etc. in the present invention are only for descriptive purposes, and cannot be construed as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features.

[0052] In the description of the present invention, unless otherwise clearly defined and limited, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0053] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0054] The present invention discloses a method for predicting the fracture toughness of a polar marine composite steel plate at different thicknesses, including the following specific steps:

[0055] S1: Material selection and performance testing: Select suitable base layer 1 and cladding layer 2 materials, conduct tensile tests on the materials according to relevant standards, and obtain basic performance data;

[0056] Ensure that the selected materials meet the usage requirements of the polar marine composite steel plate, use the tensile test to provide the basic mechanical property data of the materials, and provide basic parameters for subsequent fracture tests and finite element simulations; this setting obtains accurate and reliable material property data through standardized tests, which helps to improve the accuracy of the prediction model.

[0057] S2: Fracture test: Prepare specimens according to standard requirements, perform notch machining, conduct fracture tests on the specimens, and obtain the fracture loads when the crack penetrates the cladding layer 2 and when the cladding layer 2 is intact;

[0058] Obtain the fracture behavior data of the composite steel plate under specific conditions through actual tests, provide verification data for the simulation, and ensure the accuracy of the simulation results. This setting can directly reflect the fracture performance of the composite steel plate under actual working conditions and provide a reliable verification basis for subsequent modeling and simulation.

[0059] S3: Modeling and simulation: Model the composite steel plate specimens with different thicknesses of the cladding layer 2, set material properties, boundary conditions, and loading methods, conduct fracture behavior simulations, extract the load-displacement curves during the simulation process, and analyze the fracture behavior;

[0060] Obtain a large number of data points by simulating the fracture behavior at different thicknesses of the cladding layer 2 for subsequent model establishment, and reveal the influence mechanism of the thickness of the cladding layer 2 on the fracture toughness. This setting has strong controllability in the simulation process, can flexibly adjust parameters to study the fracture behavior under different working conditions, has low cost and short cycle, and has higher efficiency compared with actual tests.

[0061] S4: Model establishment and parameter fitting: Based on the fracture test and simulation results, establish a fracture toughness prediction model, and fit the undetermined parameters in the model, such as A1, A2, X0, p, etc.;

[0062] Construct a mathematical model that can describe the relationship between the thickness of the cladding layer 2 and the fracture toughness, and make the model more accurately reflect the actual situation by fitting parameters. This set model is universal and can be applied to the prediction of the fracture toughness of composite steel plates with different thicknesses of the cladding layer 2. The parameter fitting process is scientific and rigorous, which improves the accuracy of the model.

[0063] S5: Model verification and application: Compare the calculated fracture toughness values obtained from the prediction model with the measured values to verify the accuracy of the model. Apply the prediction model to predict the fracture toughness of composite steel plates with different thicknesses of the cladding layer 2, providing a basis for anti-fracture design.

[0064] Through comparison and verification, ensure the reliability and accuracy of the prediction model, and improve the effectiveness of the model in practical applications.

[0065] Specifically, in step S1, the material of the base layer 1 is FH40, and the material of the cladding layer 2 is 317L stainless steel.

[0066] As the material of the base layer 1, FH40 has high strength and toughness, and can withstand the extrusion and impact of ice layers in the polar environment, providing sufficient structural support for the composite steel plate. As the material of the cladding layer 2, 317L stainless steel has good corrosion resistance and wear resistance, and can effectively resist the erosion of polar seawater and the wear of ice layers, protecting the base layer 1 material from damage. Obtain the basic performance data of FH40 and 317L stainless steel through tensile tests, such as density, yield strength, tensile strength, elastic modulus, Poisson's ratio, etc. These data are the basis for subsequent fracture tests and finite element simulations.

[0067] The combination of FH40 and 317L stainless steel in this setting realizes the complementarity of strength and corrosion resistance, enabling the composite steel plate to not only withstand large external forces but also resist the erosion of harsh environments, and has stable and reliable performance, is easy to obtain and process, which is conducive to reducing production costs and improving production efficiency.

[0068] Preferably, the thickness of the cladding layer 2 is 8 mm.

[0069] By studying the fracture behavior at a cladding layer 2 thickness of 8 mm, a prediction model applicable to different cladding layer 2 thicknesses can be established. This model has a wider applicability and can guide the design and application of composite steel plates with different cladding layer 2 thicknesses. The 8 mm cladding layer 2 thickness is representative in polar marine composite steel plates and can reflect common situations in actual engineering applications. Selecting this thickness for research helps to obtain fracture toughness data with practical significance. Compared with conducting experiments on multiple different cladding layer 2 thicknesses one by one, selecting 8 mm as the reference thickness for experiments can significantly reduce the experimental cost and time cost.

[0070] Specifically, in step S1, a tensile test is conducted on the clad steel plate in accordance with GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", and the obtained data includes material density, yield strength, tensile strength, elastic modulus, Poisson's ratio, plastic parameters, and Maxpe damage criterion parameters.

[0071] Density: It is used to calculate the material mass, evaluate the self-weight of the structure, and provide a basis for defining the mass properties of the finite element model.

[0072] Yield strength: It reflects the critical stress at which the material enters plastic deformation and is a basic index for evaluating the load-bearing capacity of the material.

[0073] Tensile strength: It characterizes the maximum load-bearing capacity of the material under tensile load and provides a reference for the ultimate strength in anti-fracture design.

[0074] Elastic modulus: It determines the stiffness of the material in the elastic stage and directly affects the simulation accuracy of the stress-strain relationship in the finite element model.

[0075] Poisson's ratio: It describes the ratio of the transverse deformation to the longitudinal deformation of the material and is crucial for simulating the stress distribution and deformation behavior at the crack tip.

[0076] Plastic parameters (such as hardening index, necking coefficient): They characterize the deformation ability of the material after entering the plastic state and provide data support for simulating the plastic zone evolution during crack propagation.

[0077] Maxpe damage criterion parameters: They quantify the damage accumulation law of the material under complex stress states and provide damage evolution description parameters for the fracture toughness prediction model.

[0078] The data obtained through standardized tests can form a material property database, providing benchmark inputs for subsequent finite element simulations, parameterization of the fracture toughness prediction model, and design verification. By comparing the test data of the FH40 base layer 1 and the 317L stainless steel clad layer 2 materials with the design standards, it is ensured that the materials meet the performance requirements of the clad steel plate for polar ships in low-temperature and highly corrosive environments. The test data provides a direct basis for assigning material properties, selecting damage criteria, and parameter fitting of the fracture toughness prediction model (such as the layer thickness ratio Rt model) in subsequent finite element simulations.

[0079] This setting can obtain the true performance data of the material through tests, avoid the distortion of fracture toughness prediction caused by deviations in material property parameter assumptions, improve the reliability of the anti-fracture design of the clad steel plate for polar ships. The standardized tests can quickly obtain material performance data, avoid repeated trial and error, significantly reduce the number of tests, and reduce the R & D cost. At the same time, accurate material data can reduce the number of model correction iterations and improve the R & D efficiency.

[0080] Specifically, in step S2, a sample of the clad steel plate is taken, a notch is machined according to the drawing, and a three-point bending fracture test is carried out in accordance with the requirements of GB-T21143-2014 "Unified Test Method for Quasi-Static Fracture Toughness of Metallic Materials". The loading span S is applied to obtain the fracture load when the crack penetrates the cladding layer 2 and when the cladding layer 2 is intact.

[0081] The fracture load when the crack penetrates the cladding layer 2 reflects the bearing limit of the clad steel plate when the material of the cladding layer 2 fails, and can be used to evaluate the interfacial bonding strength between the cladding layer 2 and the base layer 1 and the anti-fracture performance of the material of the cladding layer 2; the fracture load when the cladding layer 2 is intact characterizes the fracture ability of the overall structure of the clad steel plate when the cladding layer 2 is not damaged, and reflects the fracture toughness dominated by the material of the base layer 1. By adjusting the span, different stress distribution states can be simulated, and detailed data on the crack propagation path and fracture mode can be obtained, providing key input parameters for the fracture toughness prediction model.

[0082] By comparing the fracture loads when the cladding layer 2 penetrates and is intact, the influence law of the thickness of the cladding layer 2 on the overall fracture toughness can be evaluated, providing a basis for optimizing the thickness design of the cladding layer 2, and can be used to calibrate the fracture criterion parameters (such as stress intensity factor, J-integral, etc.) in finite element simulation, improving the accuracy of the prediction model.

[0083] This standardized test process helps to ensure data reliability, has high test efficiency and strong working condition relevance, and can significantly improve the scientificity and reliability of the anti-fracture design of the clad steel plate for polar ships.

[0084] Preferably, in the three-point bending fracture test, at least two support rollers 4 are placed horizontally, the cladding layer 2 faces the support rollers 4, and the loading roller 3 is arranged above the base layer 1. During the test, the loading roller 3 applies a load to the base layer 1.

[0085] With this test device setting, the bending stress state that the material may encounter during actual use can be more realistically simulated, the stress-strain relationship of the material under the action of the bending load can be accurately measured, and then the key mechanical property indexes such as the bending strength and elastic modulus of the material can be determined.

[0086] This setting is easy to operate, can draw a load-displacement curve, intuitively reflect the bending performance of the material, and has good repeatability between different tests.

[0087] Preferably, the total crack length is taken as 13 mm, and S = 4W.

[0088] Meet the recommended range of prefabricated crack length (usually 20% - 60% of the specimen width W) in international fracture mechanics test standards (such as ASTM E1820, GB / T 21143). A crack length of 13 mm can ensure the full development of the stress field at the crack tip, avoid premature failure of the specimen, and ensure the stability of the fracture toughness test results; a crack length of 13 mm can penetrate the cladding layer 2 (such as 8 mm thick 317L stainless steel) and extend to the base layer 1 (FH40 steel), covering the entire process of interfacial crack propagation in the composite steel plate, fracture of the cladding layer 2, and dominant fracture of the base layer 1, providing key data for studying the influence of the layer thickness ratio Rt on fracture toughness; in the three-point bending test, the ratio of the span S to the specimen width W (S / W) directly affects the calculation accuracy of the stress intensity factor (K). S = 4W is a classic span ratio in fracture mechanics tests, which can ensure that the stress field at the crack tip conforms to the theoretical assumptions of linear elastic fracture mechanics (LEFM), making the fracture toughness test results highly consistent with the theoretical model. The span ratio of S = 4W can ensure a uniform stress field distribution at the crack tip, avoid local yielding of the specimen due to too small a span or insufficient crack tip constraint due to too large a span, and thus accurately reflect the fracture mechanism of polar ship composite steel plates under loads such as ice impact and wave impact.

[0089] The combination of setting the total crack length to 13 mm and the loading span S = 4W significantly improves the accuracy, efficiency, and applicability of the fracture toughness prediction of polar ship composite steel plates by standardizing test conditions, accurately simulating fracture behavior, and parameterizing support models. It can ensure that the test data error is less than 5% and the error between the model prediction results and the actual working conditions is less than 10%, providing reliable technical support for the anti-fracture design, safety assessment, and life prediction of polar ship composite steel plates.

[0090] Specifically, in step S3, finite element software is used to model composite steel plate specimens with different cladding layer 2 thicknesses.

[0091] By using finite element simulation (FEA) to replace a large number of tests with different cladding layer 2 thickness gradients (such as cladding layer 2 thicknesses of 4 mm, 6 mm, and 8 mm), it reduces material consumption, equipment occupancy, and labor costs. The cost of a single simulation is only 1 / 10 - 1 / 5 of that of physical tests. It can quickly adjust parameters such as the cladding layer 2 thickness, interfacial bonding strength, and crack length, obtain multiple groups of data, and accelerate the parameterization process of the fracture toughness prediction model. Finite element modeling significantly improves the accuracy, efficiency, and applicability of the fracture toughness prediction of polar ship composite steel plates through virtualized tests, multi-parameter coupling analysis, and efficient data extraction. The finite element model verified by experimental data can achieve: reducing the prediction error of the layer thickness ratio Rt model; improving the fracture toughness prediction accuracy by 40% under complex working conditions (low temperature, dynamic load); shortening the R & D cycle and reducing costs.

[0092] This setting features high precision and flexibility, enabling efficient acquisition of multi-dimensional data and shortening the R & D cycle.

[0093] Preferably, the finite element software can be ABAQUS or ANASYS.

[0094] Specifically, in step S3, the finite element model keeps the total size and the total crack length unchanged, only changing the layer thickness ratio. The thickness of the cladding layer 2 is taken at intervals of 1 mm. The interface is simplified to a bonded contact, and the rest are sliding friction contacts. The model mesh element type is an eight-node linear hexahedron element (C3SD8R), and the mesh division strategy is dense in the middle and sparse at both ends.

[0095] By fixing the total model size (such as specimen width W = 25 mm, thickness B = 12 mm) and the total crack length (such as 13 mm), and only changing the thickness of the cladding layer 2 (t1 = 3 mm / 4 mm / ... / 8 mm, the thickness of the base layer 1 t2 = B - t1), the single-variable effect of the layer thickness ratio Rt = t1 / t2 on the fracture toughness can be systematically studied. The interface is simplified to a bonded contact (T ie ) and a sliding friction contact (Coulomb friction coefficient μ = 0.3), and the working conditions of complete interface bonding and local slip can be respectively simulated to evaluate the effect of the interface bonding strength on the crack propagation path. The division method of being dense in the middle (crack tip mesh size 0.05 mm) and sparse at both ends (global mesh size 1 mm) can not only ensure the solution accuracy of the stress field at the crack tip but also greatly reduce the calculation amount.

[0096] This setting realizes multi-condition simulation by adjusting a single variable, which can reduce the specimen preparation and testing time by 80% compared with physical tests, significantly reducing the R & D cycle and investment in funds.

[0097] Preferably, the extended finite element method (XFEM) embedded in ABAQUS is used in the calculation simulation process. A quasi-static analysis step is adopted, allowing crack propagation, and the failure criterion adopts the Maxpe damage criterion.

[0098] The extended finite element method (XFEM) allows cracks to freely expand along any path (such as through the cladding layer 2, the interface, or the base layer 1) by introducing discontinuous enhancement functions into the standard finite element mesh, eliminating the grid dependence. The Maxpe damage criterion is applied based on the combination of stress triaxiality and equivalent plastic strain, which can quantitatively describe the damage accumulation process of materials under complex stress states and accurately predict the critical conditions for crack initiation and propagation.

[0099] This setting combines ABAQUS-XFEM with the Maxpe damage criterion to achieve efficient, accurate, and low-cost prediction of the fracture toughness of polar marine composite steel plates through crack propagation along arbitrary paths, physical and chemical damage evolution, and parametric modeling design.

[0100] Specifically, in step S4, the specific form of the fracture toughness prediction model is as follows:

[0101] ...................................................(1)

[0102] ................................(2);

[0103] Where: t1 is the thickness of the cladding layer 2;

[0104] t2 is the thickness of the base layer 1;

[0105] R t is the layer thickness ratio;

[0106] S is the specimen span;

[0107] W is the specimen width;

[0108] B is the specimen height;

[0109] a0 is the crack length;

[0110] Obtained through Appendix B of GB-T 21143-2014 "Metallic materials - Unified test method for quasistatic fracture toughness";

[0111] A1, A2, X0, p are undetermined parameters.

[0112] The model parameters A1, A2, X0, p can be determined by fitting a small amount of test data, avoiding a large number of physical tests, and can predict the fracture toughness under different cladding layer 2 thicknesses and crack lengths, guiding the optimization design of the layer thickness ratio of the composite steel plate.

[0113] The set fracture toughness prediction model realizes the fracture toughness prediction with high precision, low cost and multi-condition coverage through the quantitative relationship between the layer thickness ratio and the crack length.

[0114] Specifically, in step S4, the undetermined parameters in the model are fitted by the least squares method.

[0115] Minimize the residual sum of squares (RSS) of the predicted value and the test value (or simulated value) to ensure that the fitting curve is optimal in a statistical sense. By fitting the functional relationship between the layer thickness ratio Rt (independent variable) and the fracture toughness KIC (dependent variable) by the least squares method, the accuracy, reliability and engineering applicability of the fracture toughness prediction model of the polar ship composite steel plate are significantly improved.

[0116] Example 1

[0117] The working process using the present invention is as follows:

[0118] 1. Prepare a clad steel plate with the maximum thickness of the cladding layer 2. In this example, the thickness of the cladding layer 2 is taken as 8 mm. According to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", FH40 is used for the base layer 1 of the clad steel plate, and 317L is used for the cladding layer 2. Samples are taken respectively for tensile testing to obtain the basic tensile property data of the base layer 1 and the cladding layer 2 of the clad steel plate, and the material density, yield strength, tensile strength, elastic modulus, Poisson's ratio, plastic parameters and Maxpe damage criterion parameters are obtained. The results are shown in Table 1, Table 2 and Table 3.

[0119] Table 1 Basic property data of materials

[0120]

[0121] Table 2 Material plastic parameters

[0122]

[0123] Table 3 Material Maxpe damage criterion parameters

[0124]

[0125] 2. Take samples of the clad steel plate and carry out notch machining according to Figure 2 and Figure 3 In this example, the total crack length is taken as 13 mm. According to the requirements of GB-T 21143-2014 "Metallic materials - Unified test method for quasi-static fracture toughness", a three-point bending fracture test is carried out. The loading span S = 4W, and the fracture loads when the crack penetrates the cladding layer 2 and when the cladding layer 2 is intact are obtained. The fracture toughness is calculated using Equation (3), F Q Take the maximum load, a0 is taken as 13 mm, Take 1.307, and the remaining dimensions are calculated according to the measured values. The calculation results are shown in Table 4.

[0126] ......(3)

[0127] Table 4 Fracture test results

[0128]

[0129] 3. According to the actual test process, use ABAQUS finite element software to model the clad steel plate samples with different thicknesses of the cladding layer 2 one by one. The finite element model is as Figure 5As shown. The length, width, and height dimensions of the model are 54 mm, 54 mm, and 270 mm. Different models keep the total size and the total crack length unchanged, only changing the layer thickness ratio. The thickness of the second composite layer is taken at intervals of 1 mm. The interface is simplified to a bonded contact, and the rest are sliding friction contacts. The extended finite element method (XFEM) embedded in ABAQUS is used for the calculation simulation process. A quasi-static analysis step is adopted, allowing crack propagation. The failure criterion uses the Maxpe damage criterion, and the basic material performance parameters are assigned according to the results in Table 1, Table 2, and Table 3. The mesh element type of the model is an eight-node linear hexahedron element (C3SD8R). The mesh division strategy is dense in the middle and sparse at both ends. The finite element model after mesh division is as shown in Figure 6 As shown. The load-displacement curve during the calculation process is extracted until the second composite layer fails, as shown in Figure 7 As shown. F = 500 kN is the measured value when the thickness of the second composite layer is 8 mm. The simulation value is relatively close, which can prove the effectiveness of the model. When the thickness of the second composite layer is 1 - 2 mm, the first base layer can still bear the load when the second composite layer fails. The load when the second composite layer fails is not the maximum load. The maximum load should be 380 kN. The maximum load is obtained as shown in Table 5.

[0130] Table 5 Calculated values of the maximum load under different thicknesses of the second composite layer

[0131]

[0132] 4. The obtained maximum load data is fitted using the least squares method, and the undetermined parameters are obtained as shown in Table 6. Substituting each parameter, the form of the prediction model is obtained as shown in Equation (4). The numerical calculation results and the model prediction results are as shown in Figure 8 .

[0133] Table 6 Values of the undetermined parameters in the prediction model

[0134]

[0135] ................................(4)

[0136] 5. The calculated values obtained from Equation (4) are compared with the measured values obtained from Table 3, as shown in Table 7. It can be seen that the deviation between the calculated fracture toughness values obtained from the prediction model and the measured values obtained from the three-point bending test does not exceed 10 MPa·m 1 / 2 , indicating that the prediction model proposed in the present invention can effectively predict the fracture toughness values of composite steel plates under different thicknesses of the second composite layer.

[0137] Table 7 Calculated and measured values of fracture toughness

[0138]

[0139] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for predicting the fracture toughness of a polar marine composite steel plate at different thicknesses, characterized in that, The specific steps are as follows: S1: Material selection and performance testing: Select the base layer (1) and cladding layer (2) materials, conduct tensile tests on the materials according to the standards, and obtain the performance data of the base layer (1) and the cladding layer (2) materials; S2: Fracture test: Prepare specimens according to the requirements, perform notch machining, conduct fracture tests on the specimens, and obtain the fracture loads when the crack penetrates the cladding layer (2) and when the cladding layer (2) is intact; S3: Modeling and simulation: Model composite steel plate specimens with different thicknesses of the cladding layer (2), set material properties, boundary conditions, and loading methods, conduct fracture behavior simulations, extract the load-displacement curves during the simulation process, and analyze the fracture behavior; S4: Model establishment and parameter fitting: Based on the fracture test and simulation results, establish a fracture toughness prediction model and fit the undetermined parameters in the model; S5: Model verification and application: Compare the calculated fracture toughness values obtained from the prediction model with the measured values to verify the accuracy of the model, and apply the prediction model to predict the fracture toughness of composite steel plates with different thicknesses of the cladding layer (2) to provide a basis for anti-fracture design.

2. The prediction method for the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that In step S1, the material of the base layer (1) is FH40, and the material of the cladding layer (2) is 317L stainless steel.

3. The method for predicting the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that, In step S1, according to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", tensile tests are conducted on the composite steel plate, and the obtained data are material density, yield strength, tensile strength, elastic modulus, Poisson's ratio, plastic parameters, and Maxpe damage criterion parameters.

4. The prediction method for the fracture toughness of the polar shipboard composite steel plate according to claim 1 at different thicknesses, characterized in that, In step S2, samples are taken from the composite steel plate, notch machining is carried out according to the drawings, and three-point bending fracture tests are conducted according to the requirements of GB-T21143-2014 "Unified test method for quasi-static fracture toughness of metallic materials", with a loading span of S, to obtain the fracture loads when the crack penetrates the cladding layer (2) and when the cladding layer (2) is intact.

5. The prediction method for the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that In step S2, the total crack length is taken as 13 mm, the specimen width is W, and the span S = 4W.

6. The prediction method of the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that, In step S3, finite element software is used to model composite steel plate specimens with different thicknesses of the cladding layer (2).

7. The method for predicting the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that, In step S3, the total size and total crack length of the finite element model remain unchanged, only the layer thickness ratio is changed. The thickness of the cladding layer (2) is taken at intervals of 1 mm. Among them, the interface is simplified to a bonded contact, and the rest are sliding friction contacts; the model mesh element type is an eight-node linear hexahedral element (C3SD8R), and the mesh generation strategy adopts a dense middle and sparse ends method.

8. The prediction method for the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that, In step S3, the calculation simulation process is carried out using the extended finite element method (XFEM) embedded in ABAQUS, with a quasi-static analysis step, allowing crack propagation, and the failure criterion adopts the Maxpe damage criterion.

9. The predicting method for fracture toughness of the polar ship composite steel plate under different thicknesses according to claim 1, characterized in that, In step S4, the specific form of the fracture toughness prediction model is: ．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．(1) ．．．．．．．．(2)； Where: t1 is the thickness of the cladding layer (2); t2 is the thickness of the base layer (1); R t is the layer thickness ratio; S is the specimen span; W is the specimen width; B is the specimen height; a0 is the crack length; Obtained from Appendix B of GB-T 21143-2014 "Unified Test Method for Quasi-Static Fracture Toughness of Metallic Materials" A1, A2, X0, p are undetermined parameters.

10. The method for predicting the fracture toughness of the polar ship composite steel plate according to claim 1 at different thicknesses, characterized in that, In step S4, the least squares method is used to fit the undetermined parameters in the model.

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