Coupled numerical simulation of low-cycle fatigue damage in metal components

Abstract

A coupled cyclic plasticity-damage model is implemented for simulating low-cycle fatigue in metal components. Constitutive relations account for J2-flow theory with nonlinear kinematic/isotropic hardening, coupled with isotropic continuum damage mechanics. The damage potential is written in a general form, allowing for implementing different damage models. An implicit numerical integration scheme is developed and the incremental update of the internal variables is achieved through the solution of a single scalar equation. Consistent linearisation of the integration algorithm is provided explicitly to guarantee robustness of the proposed algorithm. The algorithm is implemented in a user subroutine and is inserted into a commercial finite element software. Its accuracy and computational efficiency are demonstrated through numerical simulation of large-scale experiments on metal piping components that failed under low-cycle fatigue loading. The numerical analyses are conducted using finite element models of different mesh density, implementing an appropriate simulation methodology. A simple and efficient damage evolution function is employed, regularised with respect to the element’s size, so that the numerical results present negligible mesh dependency. Excellent comparison is observed between experimental and numerical results in terms of global structural response, local strains and the number of cycles for developing through-thickness crack, indicating that the present formulation can be used as an efficient numerical tool for simulating inelastic damage and low-cycle fatigue in large-scale metal structural components.