CN-120526905-B - Fatigue life prediction method based on physical failure mechanism in liquid lead bismuth environment

CN120526905BCN 120526905 BCN120526905 BCN 120526905BCN-120526905-B

Abstract

The invention relates to a fatigue life prediction method based on a physical failure mechanism in a liquid lead-bismuth environment, which comprises the following steps of establishing a representative volume unit model, defining units belonging to a slip zone, defining a crystal plasticity constitutive equation, determining parameters in the crystal plasticity constitutive equation, calculating an average shear strain range of the slip zone, carrying out a fracture toughness test to obtain specific fracture energy, establishing a fatigue life prediction model based on the physical failure mechanism, carrying out a low-cycle fatigue test on a metal material in a high-oxygen liquid lead-bismuth environment at a prediction temperature, determining an oxide film thickness, establishing a fatigue life prediction model in a high-oxygen liquid lead-bismuth environment, and predicting the fatigue life of the metal material in the high-oxygen liquid lead-bismuth environment. According to the invention, a low-cycle fatigue test for marking the crystal plasticity constitutive equation parameters in the air at the predicted temperature is carried out, and a fracture toughness test in the air and liquid lead bismuth environment is carried out, so that the fatigue life in the liquid lead bismuth environment can be predicted.

Inventors

SHI SHOUWEN
LI WEIBIN
WU DAN
HUANG WEI
CHEN GANG
LIN QIANG
CHEN XU

Assignees

天津大学

Dates

Publication Date: 20260508
Application Date: 20250520

Claims (5)

1. A fatigue life prediction method based on a physical failure mechanism in a liquid lead bismuth environment is characterized by comprising the following steps: Step 1, a representative volume unit model is established, random orientation is given, and units belonging to a sliding band are defined; Step 2, defining a crystal plasticity constitutive equation: Defining a crystal plasticity constitutive equation of the material in a uniaxial symmetry cycle low-cycle fatigue test through a user subroutine UMAT, so as to describe the stress-strain relationship of the representative volume unit model in the step 1 under the uniaxial symmetry cycle load; Step 3, determining parameters in a crystal plasticity constitutive equation through a cyclic stress amplitude curve or a fatigue hysteresis loop of a test: carrying out a low cycle fatigue test of symmetrical cycle on the metal material in an air environment at a predicted temperature to obtain a cyclic stress amplitude curve or a fatigue hysteresis loop of the test; Determining parameters in the crystal plastic constitutive equation by a parameter test method, and comparing the cyclic stress amplitude curve or the fatigue hysteresis loop obtained by finite element calculation under the air environment with a curve obtained by a test under the air environment until the fitting degree of the cyclic stress amplitude curve or the fatigue hysteresis loop obtained by finite element calculation and the cyclic stress amplitude curve or the fatigue hysteresis loop obtained by the test converges; step 4, calculating the average shear strain range of the slip zone according to the unit of the slip zone defined in the step 1: According to the representative volume unit model in the step 1 and the crystal plasticity constitutive equation parameters determined in the step 3, calculating the shear strain range of units contained in the sliding band, averaging to obtain the shear strain range of the sliding band, sequencing the shear strain ranges of all the sliding bands, and taking the maximum value of the shear strain ranges for subsequent fatigue life prediction; Step 5, carrying out fracture toughness tests of corresponding environments to obtain specific fracture energy; Step 6, a fatigue life prediction model based on a physical failure mechanism is established, fatigue life prediction is carried out according to the established model and the data of the steps 4 and 5, and the fatigue life of the metal material in the air and low-oxygen liquid lead bismuth environment is predicted; Step 7, carrying out a low cycle fatigue test of symmetrical cycle on the metal material in a predicted temperature high-oxygen liquid lead bismuth environment to determine the thickness of the oxide film; Step 8, a fatigue life prediction model under the high-oxygen-concentration liquid lead bismuth environment is established, and the fatigue life of the metal material under the high-oxygen-concentration liquid lead bismuth environment is predicted according to the established model and the data of the steps 4 to 7: , Height of extrusion at the surface of metallic material When the thickness of the oxide film is equal to that of the oxide film in the step 7, the oxide film of the metal material is considered to be destroyed, and the extrusion height of the metal material on the circularly loaded lower surface is as follows: , Wherein, the Is the fatigue life of the high oxygen concentration liquid lead bismuth environment, In the form of a poisson's ratio, In order to be specific to the energy of the fracture, In order to achieve a shear modulus, the polymer is, Is one-half of the grain size of the crystal grains, For the slip system to be in the shear strain range, For the thickness of the oxide film, In order to be an irreversible slip coefficient, Is a general constant of 2.78, The value range of the composite index is 0.5 to 1 according to the randomness degree of the sliding process in the sliding band; To cycle the extrusion height of the metallic material surface during loading, For the number of cyclic loads.
2. The method of claim 1, wherein the step 1 creates a two-dimensional representative volume unit model containing a plurality of grains, each grain being given a random crystal orientation, using ABAQUS finite element software, and describes microstructure information of the metal material, rotates the grains by rotating the matrix, defines an intersection line of the rotated sliding surface and a plane of the finite element model as a sliding band, considers only the sliding band passing through a centroid of the grains, and calculates a distance from a center of each unit in the grains to the intersection line, and if the distance is equal to or smaller than a size of one unit, determines the unit as a unit belonging to the sliding band.
3. The method for predicting fatigue life based on physical failure mechanism in liquid lead bismuth environment according to claim 1, wherein the crystal plasticity constitutive equation adopted in the step 2 is: , , , , , , , , , Wherein, the Is the first The plastic slip ratio of the slip system is set, For the purpose of the reference strain rate, Is the first The breaking shear stress of the sliding system is calculated, Is the first The back stress of the slip system is calculated, Is the first The critical decomposition shear stress of the sliding system, As a parameter of sensitivity to strain rate, As a function of the stress tensor, And Respectively the first Slip direction vector and slip plane normal vector of the slip system, In order to be able to harden the parameters directly, In order for the coefficient of dynamic recovery to be, To control A monotonic term evolving under a monotonic deformation, In order to cycle through the softening point of the product, For the modulus of latent hardening the composition, Is the first The plastic slip ratio of the slip system is set, Is the latent hardening coefficient, representing the latent hardening modulus And self-hardening modulus Ratio of (1), parameter , And The initial hardening modulus, the initial critical decomposition shear stress and the saturation stress, For the total cumulative shear strain of all slip trains, For saturation softening, i.e. the maximum reduction in critical decomposition shear stress caused by cyclic softening effect, And In order to cycle the softening parameter in-between, Plastic strain is accumulated for cycling.
4. The method for predicting fatigue life based on physical failure mechanism in liquid lead bismuth environment according to claim 1, wherein in step 5, fracture toughness test of the metal material in air and low oxygen concentration liquid lead bismuth environment at the predicted temperature is performed to obtain fracture toughness of the metal material in the corresponding environment, and then specific fracture energy is obtained according to the relationship that the specific fracture energy is one half of the fracture toughness, wherein the specific fracture energy is obtained from the fracture toughness test, and the specific fracture energy value is one half of the fracture toughness value.
5. The fatigue life prediction method based on the physical failure mechanism in the liquid lead bismuth environment according to claim 1, wherein in the step 6, a fatigue life prediction model in the air and low oxygen concentration liquid lead bismuth environment is established based on a Tanaka-Mura model: , in the formula, Is the fatigue life of air or low-oxygen concentration liquid lead bismuth environment, In the form of a poisson's ratio, In order to be specific to the energy of the fracture, In order to achieve a shear modulus, the polymer is, Is one-half of the grain size of the crystal grains, Is a shear strain range of a slip system, wherein the Poisson's ratio Shear modulus One half of the grain size Is determined according to the inherent property of the metal material, and the shear strain range of the sliding system According to the determination in step 4, specific breaking energy According to the determination in the step 5, the law of the fatigue life of the metal in the low-oxygen concentration liquid lead bismuth and the air environment is kept consistent, and the fatigue life of the metal in the low-oxygen concentration liquid lead bismuth and the air environment can pass through the fatigue life prediction model Predicting fatigue life; Calibrating the crystal plasticity constitutive equation parameters through a symmetrical low cycle fatigue test in the air environment in the step 3, and calibrating the shearing strain range of a sliding system in a sliding zone in the step 4 And step 5, determining the specific fracture energy of corresponding environments through fracture toughness tests in air and low-oxygen concentration liquid lead bismuth Determining poisson's ratio by combining inherent properties of metal material Shear modulus And one half of the grain size Substituting fatigue life prediction model The low cycle fatigue life of metallic materials in air and low oxygen concentration liquid lead bismuth environments was predicted.

Description

Fatigue life prediction method based on physical failure mechanism in liquid lead bismuth environment Technical Field The invention relates to the technical field of metal material fatigue life prediction in a liquid lead bismuth environment, in particular to a fatigue life prediction method based on a physical failure mechanism in the liquid lead bismuth environment. Background The lead-cooled fast reactor of one of the fourth generation nuclear energy system reactor types adopts closed fuel circulation, has excellent nuclear waste transmutation and nuclear fuel proliferation capability, and has the advantages of excellent neutron and thermal characteristics, no reaction with water and air and the like as a liquid lead-bismuth eutectic (LBE) of a coolant. Therefore, the lead cold fast reactor can well meet the target requirement of the fourth generation nuclear energy system, and is internationally recognized as an important option for realizing the development of nuclear energy. However, incompatibility between the structural material and liquid lead bismuth can lead to embrittlement of the liquid metal, which presents a significant challenge for the development of lead cooled fast stacks. Temperature changes and pressure fluctuations in operation of a nuclear power plant during operation can subject components to cyclic loads, resulting in low cycle fatigue failure. The fatigue life of the structural material is obviously reduced in a liquid lead bismuth environment. Therefore, in order to ensure safety and economy, it is important to accurately predict the fatigue life of the material in a liquid lead bismuth environment. The current method for evaluating the metal fatigue life in the liquid lead bismuth environment is not more, is based on an empirical model, and needs to be fitted on the basis of a series of test data. However, the fatigue life prediction model based on the physical failure mechanism does not describe the embrittlement phenomenon of the liquid metal, and may not be suitable for the liquid lead bismuth environment. In addition, the influence of an oxide film generated on the surface of a metal material in a high-oxygen-concentration liquid environment on the fatigue life is not described in a model at present. Aiming at the technical problems, the invention provides a fatigue life prediction method based on a physical failure mechanism in a liquid lead bismuth environment. Disclosure of Invention The invention aims to overcome the defects of the prior art, and provides a fatigue life prediction method based on a physical failure mechanism in a liquid lead bismuth environment, which can predict the fatigue life of air and a low-oxygen concentration liquid lead bismuth environment by only carrying out a low-cycle fatigue test for marking crystal plasticity constitutive equation parameters in prediction temperature air and a fracture toughness test in the air and the liquid lead bismuth environment, and can predict the fatigue life of an oxide film by determining the thickness of a small amount of low-cycle fatigue tests in the high-oxygen concentration liquid lead bismuth environment. The invention solves the technical problems by the following technical proposal: A fatigue life prediction method based on a physical failure mechanism in a liquid lead bismuth environment comprises the following steps: Step 1, a representative volume unit model is established, random orientation is given, and units belonging to a sliding band are defined; Step 2, defining a crystal plasticity constitutive equation: Defining a crystal plasticity constitutive equation of the material in a uniaxial symmetry cycle low-cycle fatigue test through a user subroutine UMAT, so as to describe the stress-strain relationship of the representative volume unit model in the step 1 under the uniaxial symmetry cycle load; Step 3, determining parameters in a crystal plasticity constitutive equation through a cyclic stress amplitude curve or a fatigue hysteresis loop of a test: carrying out a low cycle fatigue test of symmetrical cycle on the metal material in an air environment at a predicted temperature to obtain a cyclic stress amplitude curve or a fatigue hysteresis loop of the test; Determining parameters in the crystal plastic constitutive equation by a parameter test method, and comparing the cyclic stress amplitude curve or the fatigue hysteresis loop obtained by finite element calculation under the air environment with a curve obtained by a test under the air environment until the fitting degree of the cyclic stress amplitude curve or the fatigue hysteresis loop obtained by finite element calculation and the cyclic stress amplitude curve or the fatigue hysteresis loop obtained by the test converges; step 4, calculating the average shear strain range of the slip zone according to the unit of the slip zone defined in the step 1: According to the representative volume unit model in the step 1 and the crystal plasticity