Abstract:

ESDU 96036 introduces a computer program, ESDUpac A9636, to determine a set of orthotropic layer thicknesses to withstand given in-plane loads and bending moments effectively. It assumes perfect bonding between the layers and applies to lay-ups symmetrical about the plate mid-plane. The layers are of composite material with continuous fibre reinforcement at 0, 90, +45 or -45 degrees to the plate edges and may have different material properties but the +45 and -45 degree layers, which occur as adjacent pairs, must have the same properties. There can be up to 20 different layer types and up to 100 plies in the laminate. A stacking sequence is initially specified and a design procedure determines layer thicknesses for that lay-up. The procedure thickens or thins layers according to certain heuristic rules based on the way they reinforce each other until a layer (or layers) is just on the point of failure. An initial set of thicknesses is found using the in-plane loads with the 45 degree layers assumed to carry the shear, and the direct loads carried by layers with fibres in the respective directions taking account of different fibre strengths in tension or compression. The sequence of lay-ups is immaterial at that stage. When the moments are applied, account has to be taken of the distance of a layer from the neutral plane and an iterative solution is required using laminated plate theory. The program will provide alternative lay-ups for comparison with the specified lay-up and also results that take into account practical ply thicknesses where the thickness of each layer type is rounded up or down to a specified standard ply thickness. Up to 20 loading systems can be considered in parallel so that reserve factors for all load cases are treated together. The input to and output from the program are illustrated by three worked examples and input data checks are explained with warning messages provided. The output includes individual layer reserve factors, stresses and strains.