research project : Initiation and fatigue crack groth in elastic-plastic materials with deformation-induced anisotropy

Metallic components are often subject to arbitrary ‘mixed-mode stresses’ in terms of time and direction. Depending on the stress history, the material can harden in a directional manner. This project investigates how the rotational and formative hardening behaviour can be determined based on the laws of elastoplasticity and how the associated fatigue crack growth can then be determined using the phase field method.

Project name Increasing the fatigue strength of additive manufactured high-pressure components
Project partner
Grantor DFG
Duration from 1.8.2022 to 30.11.2025

Research field
 M+M

(E+E > Energy + Environment
I+I > Information + Intelligence
M+M > Matter + Materials)
Project content The aim of the project is to simulate fatigue crack growth using the phase field method and to investigate the influence of work hardening on crack initiation and propagation in metallic materials. The theoretical objectives include the thermodynamically consistent formulation of an elastoplasticity model coupled with damage rules. The model should take into account isotropic, kinematic, rotational and formative work hardening. Damage is modelled using a scalar variable and its gradient, which corresponds to the approaches of phase field theory. Non-standard thermodynamics is assumed to be a suitable thermodynamic framework. The central points of this part are the modelling of anisotropy in the flow rule and the formulation and investigation of the approaches for the phase field, as well as the generalisation of the model to large deformations. The experimental objectives include tests on the materials hardening behaviour and the fatigue behaviour with different specimen geometries. The focus here is on the experimental acquisition of the rotation of flow curves. The numerical objectives include the integration of material and field equations using the finite element method and the development of an extrapolation method for calculating large numbers of cycles. The special features of this part lie in the integration of elastoplasticity equations with dependence on the damage gradient.