A progressive quadratic failure criterion for a laminate

The application of failure criteria to laminated composites is a critical step in the determination of the strength and safety of a point in a structure under combined loading conditions. Non-homogeneous stresses within a structure may induce a complicated failure scenario whereby one ply at a point can initiate failure and affect other plies at the same point or the same ply at a neighboring point. After the first-ply failure, the stiffness of the ply is reduced by either matrix or fiber failures. The strength of the laminate at the same point is evaluated again to see if the laminate can carry an additional load. This ply-by-ply analysis progresses until the ultimate strength of the laminate is reached. The process can be extended to structures subjected to non-homogeneous stresses where both ply-by-ply and point-to-point strength analyses are progressively applied. (C) 1998 Elsevier Science Ltd. All rights reserved.