An elasto-plastic damage accumulation model for predicting the fatigue
life of ductile materials at the yield stress
Abstract
From the massive fatigue test data analysis, we find there is a big
mismatch between the fatigue life predictions done by the stress-based
method (SN) and those by the strain-based method (εN) at the material’s
yield stress, namely the moderate-cycle fatigue. As derived from the
test data, the SN and εN methods are most widely used in engineering
applications. Thus, it is necessary to address this discrepancy between
the SN and the εN at material’s yield stress. For ductile metals, the
moderate-cycle fatigue is a damage accumulation process in which the
elastic strain and plastic strain are comparable. Yield stress is a
critical point where the elastic deformation transits to the plastic
deformation. Based on a normalized damage concept, we propose a
data-driven approach, an elasto-plastic damage accumulation model, to
address the fatigue life prediction at the yield stress. By
differentiating the damages caused by the elastic and plastic behaviors,
the fatigue damage of each loading cycle is formulated as a function of
both stress and strain amplitudes. With introducing the strain energy
density-based weighting factor for the elastic and plastic behaviors,
the proposed model can accord well with the classical methods from
low-cycle fatigue to high-cycle fatigue. When it comes to the material’s
yield stress, the fatigue life predicted by the proposed model compares
favorably with the test data of two different alloys. Therefore, beyond
clarifying the mismatch between the classical approaches at the yield
stress, the proposed model is expected to find extensive applications in
fatigue design and damage evaluation of structures and materials at the
yield stress.