3-DIMENSIONAL FINITE-ELEMENT ANALYSIS OF FREE-EDGE STRESSES AND DELAMINATION OF COMPOSITE LAMINATES

A 24-node, 64-degree-of-freedom, solid hexahedronal finite element is used to analyze the interlaminar free edge stresses and delamination o f composite laminated plates. The difficulty due to the requirement of large storage space which is frequently encountered in the modeling o f contoured delamination problems is resolved by using the preconditio ned 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 i n Storage space required, thereby making the numerical analysis of the complicated contoured delamination problem feasible as well as effect ive. To evaluate the accurateness of the present formulation, numerica l algorithm and computer program, free edge stress analyses are perfor med for a [0/90], cross-ply and a [+/-45], angle-ply laminated plate. Both plates are subjected to an axial tensile strain loading. The pres ent three-dimensional results are found to be in good agreement with t hose 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 rectangula r laminated plate subjected to tensile strain is studied. Two initial delaminations are assumed to be located in the midspan of the two oppo site free edges and also at the middle of the thickness. The delaminat ion contour is assumed to be a straight line segment joined by two cir cular arcs. The strain energy release rates along the delamination fro nt are calculated using the modified crack closure method. As a step b eyond the solution using quasi-3D assumption, the present results show the non-uniform distribution of mode I strain energy release rate G(I ) along the boundary of the delamination front which fluctuates to a m aximum value when approaching both ends at the free edge of the lamina te.