Finite-element simulation of multi-axial fatigue loading in metals based on a novel experimentally-validated microplastic hysteresis-tracking method

Abstract

We propose a new approach to the prediction of multiaxial fatigue with proportional and non-proportional loading based on a recently developed three-dimensional small-strain microplasticity-based constitutive theory. The core idea of the theory is to incorporate pre-full-yield microplastic deformations in a computationally efficient way. Fatigue life is then correlated to the accumulated (micro)plastic work, which is obtained from the total plastic dissipation. The constitutive parameters required are calibrated using just a monotonic stress-strain curve determined from a simple compression test experiment together with a low cycle uniaxial fatigue experiment. The resulting three-dimensional constitutive model has also been implemented into the Abaqus/Explicit finite element program through a vectorized user-material subroutine interface with a fully-implicit, unconditionally-stable and robust time integration scheme. Using the suitably-calibrated constitutive model, a series of uniaxial and multiaxial stress- and strain-based, constant-amplitude fatigue finite element simulations have been conducted to compare with the physical experiment data from the literature. It is shown that the developed theory and its finite-element implementation (which have fewer parameters than cycle counting based methods) are able to better predict the experimental fatigue life under multiaxial proportional or non-proportional loading conditions.