Instrumented indentation test method for fracture toughness of martensitic heat-resistant steel with fused meso-damage model
By integrating the instrumented indentation testing method with the GTN microscopic damage model, the problems of destructiveness and insufficient accuracy of traditional testing methods are solved, and in-situ accurate testing of fracture toughness of martensitic heat-resistant steel is realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF MECHANICS CHINESE ACAD OF SCI
- Filing Date
- 2026-05-14
- Publication Date
- 2026-08-04
AI Technical Summary
Traditional fracture toughness testing methods destroy structural integrity and cannot be tested in situ. Furthermore, existing indentation testing methods disconnect macroscopic mechanical response from microscopic damage mechanism, resulting in insufficient accuracy and reliability of test results.
An instrumented indentation testing method integrating the GTN micro-damage model was adopted to obtain the intrinsic elastoplastic parameters and microstructure information of martensitic heat-resistant steel through micron-level indentation and electrochemical testing, and the fracture toughness was calculated by combining the results with finite element simulation.
It enables in-situ, accurate, and non-destructive testing of the fracture toughness of martensitic heat-resistant steel, improving testing accuracy and versatility.
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Figure CN122505698A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of material mechanical property testing and non-destructive testing technology, specifically involving an instrumented indentation test method for fracture toughness of martensitic heat-resistant steel that integrates a microscopic damage model. Background Technology
[0002] Martensitic heat-resistant steel, due to its excellent high-temperature creep strength and oxidation resistance, is widely used in core pressure-bearing components such as the main steam pipes of ultra-supercritical generator units. Under long-term high-temperature and complex stress conditions, martensitic heat-resistant steel gradually undergoes structural aging and performance degradation. Fracture toughness is a core indicator for assessing its operational safety and remaining service life. However, traditional fracture toughness testing methods (such as compact tensile or three-point bending tests) require cutting and preparing standard specimens, thus destroying the integrity of the tested structure. In recent years, instrumented indentation technology, with its advantages of minimal damage, portability, and in-situ testing, has become an important means of detecting the mechanical properties of in-service structures / materials, demonstrating enormous application potential in the safety evaluation of major equipment.
[0003] While instrumented indentation techniques are relatively mature in detecting hardness and elastic modulus, they still have significant limitations in accurately detecting the fracture toughness of ductile metals such as martensitic heat-resistant steel. Most existing methods rely on empirical or semi-empirical formulas (such as the indentation energy method and the characteristic parameter correlation method). These methods only establish a functional fitting relationship between indentation energy and macroscopic fracture energy, failing to deeply reveal the true physical mechanism of ductile fracture in materials. In fact, the ductile fracture of martensitic heat-resistant steel is essentially a microscopic damage evolution process involving the nucleation, growth, and aggregation of microscopic pores. Traditional indentation fracture toughness testing methods sever the intrinsic connection between macroscopic mechanical response and microscopic damage mechanism, resulting in a lack of solid physical and mechanical foundations. This not only lacks universality for martensitic heat-resistant steel under different aging conditions but also makes it difficult to meet engineering requirements in terms of accuracy and reliability. Therefore, there is an urgent need in this field for a novel testing method that can deeply couple the microscopic damage mechanism with the indentation mechanical response to achieve in-situ, accurate, and non-destructive testing of the fracture toughness of martensitic heat-resistant steel. Summary of the Invention
[0004] To address the shortcomings of traditional fracture toughness testing methods, such as sampling that damages structural integrity and the inability to perform in-situ testing, as well as the low accuracy of existing indentation testing methods that separate macroscopic mechanical response from microscopic damage mechanisms, this invention provides an instrumented indentation testing method for fracture toughness of martensitic heat-resistant steel that integrates a microscopic damage model. This method obtains the intrinsic elastoplastic parameters of martensitic heat-resistant steel through instrumented indentation testing and quantitatively obtains the key second-phase particles (M...) in the microstructure of martensitic heat-resistant steel through electrochemical testing. 23The volume fractions of C6 and Laves phases were then used to determine the fracture toughness considering GTN micro-damage established in this invention. The fracture toughness is calculated from the calculation expression. This invention overcomes the shortcomings of existing methods and achieves in-situ, accurate, and non-destructive testing of the fracture toughness of martensitic heat-resistant steel.
[0005] The technical concept of this invention is as follows: The GTN microscopic damage model is introduced into the finite element simulation analysis of martensitic heat-resistant steel, considering the microscopic damage evolution of martensitic heat-resistant steel during micron-level indentation and compact stretching processes, and the second-phase particles M of the martensitic heat-resistant steel are included. 23 The relationship between the volume fraction of C6 and Laves phases and the degree of damage was established, leading to a method for in-situ, accurate, and non-destructive testing of the fracture toughness of martensitic heat-resistant steel with a clear microscopic damage mechanism. The GTN (Gurson-Tvergaard-Needleman) microscopic damage model is a classic constitutive model in microscopic damage mechanics used to describe the damage and fracture behavior of ductile metallic materials. Its core idea is a continuous medium damage model based on micropore evolution, linking the nucleation, growth, and aggregation processes of micropores within the material with macroscopic mechanical responses. By coupling porosity evolution with a modified plastic yield criterion, it can effectively describe the entire process from damage initiation to final fracture in ductile metals.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] An instrumental indentation test method for fracture toughness of martensitic heat-resistant steel integrating a microscopic damage model includes the following steps:
[0008] The first step is to use an instrumented micron-sized indenter with a spherical indenter to perform an indentation test on the martensitic heat-resistant steel to obtain the indentation load-depth curve.
[0009] The second step is to determine the yield strength and hardening index by using the plastic parameter indentation inversion calculation expression based on the indentation load-depth curve.
[0010] The third step involves using a portable electrochemical workstation to conduct electrochemical tests on the indentation test area, measuring the M particles (second phase particles) in the martensitic heat-resistant steel. 23 Volume fractions of C6 and Laves phases;
[0011] Step 4: The yield strength, hardening index, and M... 23 Substituting the volume fractions of C6 and Laves phase into the fracture toughness calculation expression, the fracture toughness is calculated.
[0012] Beneficial effects:
[0013] This invention eliminates the need for destructive material cutting and sample preparation. Fracture toughness can be directly determined by in-situ instrumented indentation tests and electrochemical measurements on in-service equipment and structures made of martensitic heat-resistant steel. Compared to traditional fracture toughness testing methods, this invention enables in-situ, non-destructive testing. Compared to other indentation testing methods, this invention measures the M2 phase particles in martensitic heat-resistant steel. 23 The volume fractions of C6 and Laves phases take into account the influence of microscopic damage evolution in martensitic heat-resistant steel, thus providing a clearer physical mechanism and higher accuracy and universality for detecting the fracture toughness of martensitic heat-resistant steel under different aging conditions. Attached Figure Description
[0014] Figure 1 This is a flowchart of an instrumented indentation test method for fracture toughness of martensitic heat-resistant steel that integrates a microscopic damage model, according to the present invention. Detailed Implementation
[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0016] like Figure 1 As shown, the instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model of the present invention includes the following steps:
[0017] The first step is to use an instrumented micron-sized indenter with an assembled spherical indenter to conduct an instrumented indentation test on the martensitic heat-resistant steel structure / material under test and obtain the indentation load-depth curve.
[0018] The second step involves using the indentation load-depth curve obtained in the first step, and employing the indentation inversion calculation expression for plastic parameters proposed in this invention for martensitic heat-resistant steel, to determine two plastic parameters: yield strength. and hardening index .
[0019] The third step involves using a portable electrochemical workstation to perform electrochemical tests on the instrumented indentation test area, measuring the second-phase particles M in the martensitic heat-resistant steel. 23 C6 volume fraction Volume fraction of Laves phase .
[0020] Step 4: The yield strength measured in step 2 and hardening index And the second-phase particle M measured in the third step 23 C6 volume fraction Volume fraction of Laves phase Substituting the fracture toughness calculation expression proposed in this invention, the fracture toughness is determined. .
[0021] Furthermore, in the first step, there are strict requirements for the indentation depth of the instrumented indentation test: the maximum indentation depth is 0.3 times the radius of the spherical indenter used.
[0022] Furthermore, in the second step, the indentation inversion calculation expression for the plasticity parameters of martensitic heat-resistant steel is shown in equation (1):
[0023] (1)
[0024] In the formula, The indentation load work (which can be obtained by integrating the indentation load-depth curve of the loading segment). The Meyer coefficient (can be obtained by double log-linear fitting of the indentation load-ideal contact radius curve of the loaded section). The indentation elastic modulus (which can be calculated from the indentation load-depth curve of the unloading section using the Oliver-Pharr method); Where is the plastic radius, For the ideal contact radius, calculate using equation (2):
[0025] (2)
[0026] In the formula, The radius of the spherical indenter used in the experiment. For maximum indentation depth, This refers to the indentation depth.
[0027] Furthermore, in the third step, the electrochemical test employs a three-electrode system, using the Hg / HgO electrode as the reference electrode, a platinum sheet as the counter electrode, and the martensitic heat-resistant steel sample under test as the working electrode. By integrating the current-time curves of each dissolution peak obtained from the test, the second-phase particles M are obtained. 23 C6 Dissolved charge density per unit area The dissolved charge density per unit area corresponding to Laves The second-phase particle M is calculated using equation (3). 23 C6 volume fraction Volume fraction of Laves phase .
[0028] (3)
[0029] Furthermore, in the fourth step, the fracture toughness proposed in this invention... The calculation expression is shown in equation (4):
[0030] (4)
[0031] Furthermore, Equation (4) is obtained by introducing the GTN micro-damage model into the finite element simulation to simulate the process of crack propagation caused by the failure of the crack tip element and fitting a large number of finite element simulation results of martensitic heat-resistant steel compact tension.
[0032] Example:
[0033] P92 steel pipes that have not been in service, P92 steel pipes that have been in service for 80,000 hours, and P92 steel pipes that have been in service for 120,000 hours were selected as the test objects. The fracture toughness values determined by the standard compact tensile method were used as reference values (the results are shown in Table 1). This is used to verify the effectiveness and accuracy of the fracture toughness indentation test method proposed in this invention.
[0034] The first step involved using an instrumented micron-sized indenter with a tungsten carbide spherical indenter with an assembly radius of 500 μm to conduct instrumented indentation tests on non-service P92 steel samples, P92 steel samples with 80,000 hours of service, and P92 steel samples with 120,000 hours of service (with the maximum indentation depth set to 150 μm) and obtain the indentation load-depth curves.
[0035] The second step involves obtaining the indentation load-depth curves of unused P92 steel samples, P92 steel samples with 80,000 hours of service, and P92 steel samples with 120,000 hours of service from the first step. This data is then processed through integration and fitting to obtain the indentation loading energy. Meyer coefficient Indentation modulus Plastic radius Ideal contact radius Then, substitute these parameters into equation (1) to calculate the yield strength. and hardening index The calculation results are shown in Table 1.
[0036] The third step involved using a portable electrochemical workstation to conduct electrochemical tests on the instrumented indentation test areas of unused P92 steel samples, P92 steel samples with 80,000 hours of service, and P92 steel samples with 120,000 hours of service. By integrating the current-time curves of each dissolution peak obtained from the tests, the second-phase particle M was obtained. 23 C6 Dissolved charge density per unit area The dissolved charge density per unit area corresponding to Laves Then, the second phase particle M is calculated using equation (3). 23 C6 volume fraction Volume fraction of Laves phase The calculation results are shown in Table 1.
[0037] The fourth step involves testing the yield strength of the non-service P92 steel specimens, the P92 steel specimens with 80,000 hours of service, and the P92 steel specimens with 120,000 hours of service, as determined in the second step. and hardening index And the second-phase particle M measured in the third step 23 C6 volume fraction Volume fraction of Laves phase Substitute into equation (4) to calculate the fracture toughness. The calculation results are shown in Table 1. The test results of P92 steel samples under three different aging conditions show that the relative error is controlled within ±13%, indicating that this invention can accurately detect the fracture toughness of martensitic heat-resistant steel.
[0038] Table 1
[0039]
[0040] The embodiments described in this specification are merely examples of implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms stated in the embodiments. The scope of protection of this invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.
Claims
1. An instrumental indentation test method for fracture toughness of martensitic heat-resistant steel integrating a microscopic damage model, characterized in that, Includes the following steps: The first step is to use an instrumented micron-sized indenter with a spherical indenter to perform an indentation test on the martensitic heat-resistant steel to obtain the indentation load-depth curve. The second step is to determine the yield strength and hardening index by using the plastic parameter indentation inversion calculation expression based on the indentation load-depth curve. The third step involves using a portable electrochemical workstation to conduct electrochemical tests on the indentation test area, measuring the M particles (second phase particles) in the martensitic heat-resistant steel. 23 Volume fraction of C6 and volume fraction of Laves phase; Step 4: The yield strength, hardening index, and M... 23 Substituting the volume fractions of C6 and Laves phase into the fracture toughness calculation expression, the fracture toughness is calculated.
2. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 1, characterized in that, The maximum indentation depth for the indentation test is 0.3 times the radius of the spherical indenter used.
3. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 1, characterized in that, The formula for calculating fracture toughness is: （4） in, For fracture toughness, For yield strength, The hardening index, This represents the volume fraction of the second-phase particles M23C6. This represents the volume fraction of the Laves phase.
4. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 1, characterized in that, In the second step, the expression for inversion using plastic parameters proposed for martensitic heat-resistant steel is as follows: （1） In the formula, To apply the applied work, This is the Meyer coefficient. To inflate the elastic modulus, Where is the plastic radius, For the ideal contact radius, For yield strength, This is the hardening index.
5. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 4, characterized in that, The Meyer coefficient is obtained by performing a double log-linear fit on the indentation load-ideal contact radius curve of the loaded section.
6. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 4, characterized in that, Indented elastic modulus The load-depth curve of the unloading section was calculated using the Oliver-Pharr method.
7. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 1, characterized in that, The electrochemical test uses a three-electrode system, with the Hg / HgO electrode as the reference electrode, the platinum sheet as the counter electrode, and the martensitic heat-resistant steel sample under test as the working electrode.
8. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model as described in claim 1, characterized in that, M obtained by electrochemical testing 23 Integrating the current-time curves of the dissolution peaks of C6 and Laves phases, the dissolution charge density per unit area was obtained, and M was calculated accordingly. 23 Volume fractions of C6 and Laves phases.
9. The instrumented indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model according to claim 1, characterized in that, The expression for calculating fracture toughness is obtained by introducing the GTN micro-damage model into the finite element simulation, simulating the process of crack propagation caused by the failure of the crack tip element, and fitting the results of a large number of compact tensile finite element simulations of martensitic heat-resistant steel.
10. An instrumental indentation test method for fracture toughness of martensitic heat-resistant steel based on a microscopic damage model according to any one of claims 1 to 9, characterized in that, Used for in-situ, non-destructive testing of in-service martensitic heat-resistant steel equipment or structures.