Transition from Small to Large Interlaminar Cracks in Fiber-Reinforced Laminated Composites.

Abstract

The boundary element method was used to determine the elastic stress distribution near the tip of a delamination crack in fiber-reinforced plastics(FRP). FRP composites were modeled by a two-dimensional laminated structure composed of isotropic matrix and orthotropic fiber. A straight crack parallel to the fiber direction is placed in the matrix and is subjected to mode I or II loading. The stress intensity factor and the energy release rate were calculated as a function of the crack length for the above inhomogeneous model, and compared with those for a homogeneous model. For large cracks, the energy release rate for the inhomogeneous model is equal to that obtained for the homogeneous model for both mode I and II loadings. For small cracks, the energy release rate is larger for the inhomogeneous model than for the homogeneous model. The transition condition from small to large cracks was defined for the cases of mode I and II. The characteristics of the elastic matrix stress distribution ahead of the crack tip for the inhomogeneous model were discussed in comparison with the solution for the homogeneous model.