The study of fatigue crack closure is very important for the prediction of fatigue crack growth. The closure behavior of fatigue cracks has been investigated mainly from experiments. However, when experimental methods cannot be applied, an analytical or numerical simulation method may be used as an alternative. In particular, the finite element (FE) numerical method has long been used for the analysis of crack closure behavior.
Useful FE analysis results have been obtained for crack closure behavior under plane stress state. However, there are few results for plane strain state and some researchers have found that crack opening stress, Sop, obtained by FE analysis under plane strain state are much lower than under plane stress state.
Park et al. have reported that the ratio of the element size to the plastic zone size, Aa/wp, is used as a criterion to determine the most appropriate mesh size to provide good numerical results. It has been shown that the mesh size has to be changed continuously as the maximum stress intensity factor, Ko,,, increases, both under plane stress state and under plane strain state.
In this thesis, an elastic-plastic finite element analysis is preformed using ABAQUS to examine crack closure behavior under plane strain state and the numerical results are compared with experimental results. Several FORTRAN and UNIX shell programs are written to perform fatigue crack growth analysis with 4-node iso-parametric element using ABAQUS.
As the crack opening stress is very low under plane strain state, the smaller mesh size is used to increase the crack opening stress under plane strain state. However, even if the mesh size is extremely fine, the opening stress is not increased so much.
The reason why the crack opening stress is very low under plane strain state is that the plastic zone size under plane strain state is very small. Because of a small plastic zone size, the residual plastic deformation under plane strain state becomes small and the crack closure will not fully occur.
It is found that the conventional FE model used to analyze the crack closure behavior under plane stress state cannot be applied for plane strain state.
