Finite Element Analysis of Plasticity- Induced Fatigue Crack Closure with Singular Element

Developing a new method is presented to compute crack opening values in planar geometries using the crack surface nodal force distribution under minimum loading as determined from finite element analyses (FEM). In this technique, two-dimensional elastic-perfectly plastic finite element analyses of middle-crack tension (MT) geometry is conducted to study fatigue crack closure and to calculate the crack opening values under plane-strain and plane-stress conditions. Triangle singular elements are used to model the head of crack tip, because singular elements would better capture the head of crack tip stress and strain gradients. Mesh refinement studies is performed on geometry with various element sizes. Next, effect of a highly refined mesh on crack opening values is noted and significantly lower crack opening values than those reported in literature were found. The calculated crack opening values are compared with values obtained using finite element analysis and more conventional crack opening assessment methodologies. It is shown that the proposed method is independent of loading increment, integration method and crack opening assessment location. The compared opening values are exposed in good agreement with strip-yield models and results of other methods.