# US 2020/0394347 A1 · Method for assessing fatigue damage and fatigue life based on abaqus

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- Number: US 2020/0394347 A1
- Document ID: US20200394347A1
- Status: Published application
- Kind: A1
- Application number: 15/931,608
- Filed: 2020-05-14
- Published: 2020-12-17
- Earliest claimed: 2019-06-12
- Assignees: Sichuan University
- Applicants: Sichuan University
- Inventors: Qingyuan WANG; Hong ZHANG; Yongjie LIU; Chong WANG; Lang LI; Chao HE
- Web page: https://patentgrep.com/patent/US20200394347A1

## CPC

- G06F 30/23: using finite element methods [FEM] or finite difference methods [FDM]
- G06F 30/10: Geometric CAD
- G06F 2111/10: Numerical modelling
- G06F 2119/02: Reliability analysis or reliability optimisation; Failure analysis, e.g. worst case scenario performance, failure mode and effects analysis [FMEA]
- G06Q 50/08: Construction
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- G06Q: INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR

## Abstract

A method for assessing fatigue damage and fatigue life based on Abaqus is provided. The micro-macroscopic scale coupled model is based on the macroscopic representative area and the microstructure characterization of the material, and the microscopic sub-model is established by the Voronoi algorithm. The algorithm has good cross-platform compatibility and portability, fundamentally solves the technical problem of micro-macroscopic multi-scale coupling and establishes and applies the multi-scale coupled model to the fatigue damage and life assessment. The micro-macroscopic multi-scale coupled fatigue damage and life assessment model and algorithm of the material is capable of both considering the fatigue damage evolution on a microscopic scale and assessing the fatigue life, as well as calculating and assessing the two physical parameters on a macroscopic scale, so as to predict the fatigue damage and life of the whole workpiece.

## Claims

### Claim 1

A method for assessing fatigue damage and a fatigue life based on Abaqus, comprising the following steps:
S1, establishing a fatigue damage and life assessment model of a material at a coupled micro-macroscopic scale; and
S2, assessing, by the fatigue damage and life assessment model, the fatigue damage and the fatigue life of the material at the coupled micro-macroscopic scale.

### Claim 2 (depends on 1)

The method for assessing the fatigue damage and the fatigue life based on the Abaqus according to claim 1, wherein, the step S1 specifically comprises the following steps:
S11, establishing, based on an actual engineering problem, a macroscopic geometric model;
S12, selecting, based on a microstructure characterization of the material, a representative area to establish a microscopic sub-model by a Voronoi algorithm;
S13, establishing, based on the macroscopic geometric model and the microscopic sub-model, a homogeneous elastic-plastic model and a crystal plasticity-based elastic-plastic constitutive model, respectively; wherein the homogeneous elastic-plastic model is based on the macroscopic geometric model, and the microstructure characterization of the material is considered in the crystal plasticity-based elastic-plastic constitutive model;
S14, calculating a microscopic damage increment of the representative area by the crystal plasticity-based elastic-plastic constitutive model, and calculating a macroscopic damage increment of the homogeneous elastic-plastic model by accumulating damage variable values;
S15, determining, by the microscopic damage increment and the macroscopic damage increment, whether the microscopic sub-model and the macroscopic geometric model are failed; when the microscopic sub-model and the macroscopic geometric model are failed, proceeding to step S16; when the microscopic sub-model and the macroscopic geometric model are not failed, proceeding to step S17;
S16, establishing the fatigue damage and life assessment model with considering the microscopic damage increment and the macroscopic damage increment; and
S17, establishing a life assessment model without considering the fatigue damage.

### Claim 3 (depends on 2)

The method for assessing the fatigue damage and the fatigue life based on the Abaqus according to claim 2, wherein, the microscopic damage increment in the step S14 is calculated by the following formula:
d

D
micro
=
1
(
1
-
D
micro
)
β


(
λ
)
m

d

t
,
where, Dmicro represents the microscopic damage increment, λ represents a crack initiation length ratio, represents an average stress, β and m represent a microscale material coefficient and a microscale stress sensitivity parameter of the material, respectively, and t represents time; and
the macroscopic damage increment is calculated by the following formula:
d

D
m

a

c

r

o
=
∑
1
N

d

D
micro
/
N
,
N
=
1
,
2
,
3


…
,
where, Dmacro represents the macroscopic damage increment, and N represents a number of crystal grains.

### Claim 4 (depends on 2)

The method for assessing the fatigue damage and the fatigue life based on the Abaqus according to claim 2, wherein, the fatigue damage and life assessment model in the step S16 is expressed by the following formula:
N
f
=
N
micro
+
N
macro
=
2


πE


γ
s
-
4

σ
2

a

(
1
-
v
2
)
π


Eft
m

(
Δ

τ
/
2
)

(
Δγ
/
2
)
+
m
β
(
1
-
α
)

(
1
+
β
)

[
σ
a

(
1
+
E
E
0
)
(
1
-
n

σ
m
)
]
-
β
,
where, Nf represents the fatigue life; Nmicro represents a microscopic crack initiation and propagation life; Nmacro represents a macroscopic steady state crack propagation life; γs represents surface free energy of the material; Δγp represents a plastic shear strain increment; Δτ represents a shear stress increment; tm represents a width of a maximum persistent slip band (PSB); f represents an energy efficiency coefficient; n, α, β and m represent a macroscale stress concentration coefficient, a macroscale stress sensitivity parameter of the material, a microscale material coefficient and a microscale stress sensitivity parameter of the material, respectively; σα and σm represent a stress amplitude and an average stress, respectively; E and E0 respectively represent an elastic modulus after being damaged and an elastic modulus before being damaged; σ represents a stress; and ν represents a crack propagation speed.

### Claim 5 (depends on 1)

The method for assessing the fatigue damage and the fatigue life based on the Abaqus according to claim 1, wherein, the step S2 specifically comprises:
S21, determining, according to a lattice type of a metal material, a number n of solution variables of the fatigue damage and life assessment model;
S22, selecting an iterative variable and a convergence and precision control parameter, and obtaining an iterative initial value of a crystal plasticity-based elastic-plastic constitutive model based on a linear algorithm;
S23, calculating the iterative variable in an nth iteration of the crystal plasticity-based elastic-plastic constitutive model based on a non-linear algorithm or a fast Fourier transform (FFT) algorithm, and obtaining the iterative variable in an (n+1)th iteration of the crystal plasticity-based elastic-plastic constitutive model and a consistent tangent stiffness matrix by an Euler integral; and
S24, assessing the fatigue damage and the fatigue life at the coupled micro-macroscopic scale based on the iterative variable in the (n+1)th iteration of the crystal plasticity-based elastic-plastic constitutive model and the consistent tangent stiffness matrix.

### Claim 6 (depends on 5)

The method for assessing the fatigue damage and the fatigue life based on the Abaqus according to claim 5, wherein, the lattice type in the step S21 comprises a face-centered cubic metal material, a body-centered cubic metal material, and a close-packed cubic metal material; a number of solution variables of the face-centered cubic metal material is 12; a number of solution variables of the body-centered cubic metal material is 48; and a number of solution variables of the close-packed cubic metal material is 6.