An elastic-plastic finite element analysis using ANSYS is performed to examine the closure behaviour of fatigue cracks under constant amplitude loading and the numerical results are then compared with experimental results. APDL (ansys parametric design language) is used to perform the fatigue crack growth analysis with plane strain 4-node iso-parametric element.
The ratio of element size to the plastic zone size, $\Delta a/ \omega_{p}$, is used as a criterion to determine the most appropriate mesh size to provide good numerical results. It is shown that the mesh size over 0.01 mm has to be changed continously as the maximum stress intensity factor the $K_{max}$ increases.
Also a new method so-called fixed crack length method, where the applied load is changed to increase $K_{max}$ while the crack length is held constant, is introduced. The value of $\Delta a/ \omega_{p}$ is a function of $K_{max}$ in the load constant method, but it is constant in the fixed crack length method.
