Residual stress and stress fields change around fatigue crack tip: Neutron diffraction measurement and finite element modeling

Abstract

The variation of residual stress and stress field induced by the irreversible deformation at the fatigue crack tip of compact tension (CT) specimen subjected to different loads are studied by finite element method (FEM) and neutron diffraction measurement (NDM). The finite element method adopts a fatigue damage model considering material hardening effect. The stress field induced by one static load after the cyclic loads and the corresponding residual stress field at fatigue crack tip are found to match the experimental measurement. The influence of the static load on the residual stress is discussed by investigating the three principal stresses, that is the longitudinal, the transverse and the normal stresses. The results show that the residual stress at crack tip is closely correlated to the static load magnitude when this magnitude is greater than the maximum fatigue load (Pmax), while this correlation does not exist for the load smaller than Pmax. Different from the residual stress, the stress field at the crack tip increases with the increase of static load. Especially when the load is less than 1 Pmax, the stress field at the crack tip mainly appears a compressive stress state. Meanwhile, the compressive residual stress ahead of the crack tip is generated after the release of the static load. Regardless of the loading history, this residual stress is dependent only on the loading magnitude.