Fatigue life estimation under variable amplitude bending using the non-local damage parameter and multisurface plasticity model

The paper presents a non-local damage parameter successfully applied to fatigue life assessment of the smooth specimens subjected to variable amplitude bending. The parameter is based on averaging the stresses over the critical plane in the material using weight function in the exponential form. Parameter of the considered weight function is identified using fatigue lives of specimens subjected to sinusoidal plane bending. The stress fields in specimens are computed taking into account non-linear kinematic hardening of the material implemented in Matlab-based algorithm. It is shown that the kinematic hardening of the material has considerable influence on the histograms of stress amplitudes under the analyzed variable loading. The stress field on the critical plane is reduced to effective stress (the non-local damage parameter) for every time variable t by the weighted averaging process. The computed history of effective stress is used by the well known damage accumulation algorithm along with two damage accumulation hypotheses (Palmgren–Miner and Serensen–Kogayev) to estimate fatigue lives. For comparison purposes, the local concept is also applied for which the calculated fatigue lives are underestimated.