Three-Dimensional Finite Element Analysis of Free Edge Stresses and Delamination of Composite Laminates

Abstract

A 24-node, 64-degree-of-freedom, solid hexahedronal finite element is used to analyze the interlaminar free edge stresses and delamination of composite laminated plates. The difficulty due to the requirement of large storage space which is frequently encountered in the modeling of contoured delamination problems is resolved by using the preconditioned conjugate gradient method. One of the advantages of this method is that there is no need to store the fill-in elements in the stiffness matrix decomposition process, which leads to a significant reduction in storage space required, thereby making the numerical analysis of the complicated contoured delamination problem feasible as well as effective. To evaluate the accurateness of the present formulation, numerical algorithm and computer program, free edge stress analyses are performed for a [0/901 cross-ply and a [+ 45], angle-ply laminated plate. Both plates are subjected to an axial tensile strain loading. The present three-dimensional results are found to be in good agreement with those obtained using an alternative quasi-three-dimensional methods. To further demonstrate the applicability of the present development, the strain energy release rate of a [+25/90], graphite-epoxy rectangular laminated plate subjected to tensile strain is studied. Two initial delaminations are assumed to be located in the midspan of the two opposite free edges and also at the middle of the thickness. The delamination contour is assumed to be a straight line segment joined by two circular arcs. The strain energy release rates along the delamination front are calculated using the modified crack closure method. As a step beyond the solution using quasi-3D assumption, the present results show the non-uniform distribution of mode I strain energy release rate G1 along the boundary of the delamination front which fluctuates to a maximum value when approaching both ends at the free edge of the laminate.