A continuum based macroscopic unified low-and high cycle fatigue model

Abstract

In this work, an extension of a previously developed continuum based high-cycle fatigue model is enhanced to also capture the low-cycle fatigue regime, where significant plastic deformation of the bulk material takes place. Coupling of the LCF-and HCF-models is due to the damage evolution equation. The high-cycle part of the model is based on the concepts of a moving endurance surface in the stress space with an associated evolving isotropic damage variable. Damage evolution in the low-cycle part is determined via plastic deformations and endurance function. For the plastic behaviour a non-linear isotropic and kinematic hardening J2-plasticity model is adopted. Within this unified approach, there is no need for heuristic cycle-counting approaches since the model is formulated by means of evolution equations, i.e. incremental relations, and not changes per cycle. Moreover, the model is inherently multiaxial and treats the uniaxial and multiaxial stress histories in the same manner. Calibration of the model parameters is discussed and results from some test cases are shown. *

Continuous-time, high-cycle fatigue model: Validity range and computational acceleration for cyclic stress

“…Furthermore, Holopainen and co-workers [11,12] formulated a CTF model for transversely isotropic materials, as well as a CTF model for anisotropic materials where the damage is modeled as a tensor field [13]. An extension to include low-cycle fatigue has also been proposed [14]. Brighenti et al [15] suggested a more general expression for the endurance surface, and demonstrated fair agreement between modeled fatigue life and experimentally observed fatigue life for a range of steel alloys subjected to nonproportional stress.…”