finite element analyses of plasticity-induced fatigue crack closure with singular element

In this paper, a new methodology is presented to calculate crack opening values in planar geometries using the crack surface nodal force distribution under minimum loading as determined from finite element analyses (FEM). Finite element analyses are frequently used to model growing fatigue cracks and the associated plasticity-induced crack closure. Two-dimensional, elastic-perfectly plastic finite element analyses of middle-crack tension (MT) geometry were conducted to study fatigue crack closure and to calculate the crack opening values under plane-strain and plane-stress conditions. Mesh refinement studies were performed on geometry with various element types. Next, effect of a highly refined mesh on crack opening values was 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 new method is independent of loading increment, integration method and crack opening assessment location. The compared opening values is exposed in good agreement with strip-yield models.

Keywords:

Fatigue , Crack closure , Plasticity , Strip-yield models , FEM