Unlike homogeneous materials, composites have heterogeneous structure with distinct interfaces. These interfaces may be classified as microscopic surfaces within a lamina and macroscopic surfaces between laminae. An accurate evaluation of the stress distribution in the boundary layer should bring about a better understanding in the failure process of composites. Furthermore, in designing composite laminates, knowledge of the macroscopic interface stress is particularly important, since delamination of macroscopic adhesive surface results in a severe drop in strength.
In this paper, an optimization procedure for the design of angle-ply laminate is offered, considering not only macroscopic behaviour as an in-plane problem but also non-uniformity of interlamina stress.
At the beginning of the design process, in-plane modulus and interlamina stress were approximated as a constraint function and an objective function, respectively. And the ply orientation was optimized by non-linear programming (SUMT method). Consequently, the following results were obtained.
A bidirectional laminate was optimized so as to minimize interlamina stress. As the design variables, the ply angle and the rigid-body rotation of a laminate from the principal axis were taken and they were determined by the optimization procedure. It is concluded that this procedure has wide applicability to various optimum design problems and is quite valuable in engineering.
