Design of composite laminates for strength, weight, and manufacturability

A procedure is presented for determining the layups of unidirectional fiber reinforced composite plates (with or without cutouts) subjected to multiple in-plane and out-of-plane loadsets, such that the plate satisfies the Tsai-Wu Quadratic Strength Failure criterion, is of low weight, and has a layup which is easy to manufacture. Additionally, the desired cure cycle is generated for thermosetting matrix composite plates such that during cure the maximum allowed temperature is not exceeded, after cure the plate is fully cured and fully compacted, and the cure is achieved in the shortest time. The design of the layup for strength and weight (utilizing a finite element method for the stress analysis) is based on the Hybrid Algorithm for Laminate Optimization, modified to result in plates in which preassigned regions are of uniform thickness. The design of the layup for ease of manufacture is based on rules. The cure cycle is determined by simulating the cure process of the thermosetting matrix with a deterministic model "controlled" interactively by an expert system. A computer code SMARTOPT was developed which combines all the above features of the design process and, for specified geometry, material properties, and applied loadsets, provides the desired layup and cure cycle. Results for sample problems were generated which demonstrate the usefulness of the computer code for designing composite plates. The results also show that with proper design, plates made of composite materials can be made lighter than plates made of metals.