THE EFFECT OF FIBER ALIGNMENT ON COMPOSITE STRENGTH .2. THE STRENGTH OF ANGLE-PLY LAMINATES

Experiments have been carried out on relatively wide angle-ply laminat e samples with very short gauge lengths. These proved to be very much stronger than samples tested in earlier work, and which form the basis for our present design with these materials. It is highly likely that the early results for strength were more indicative of edge effects t han true laminate strength. This is confirmed by data from tests on pr essurized tubes. A review of the literature on this shows that such te sts produced results which can be an order of magnitude higher than th e early laminate tests. Thus our design calculations could well be sev erely underestimating the potential strength of angle-ply laminates. T his may be having serious consequences for the aerospace industry, thr ough the use of design criteria for strength which may be too conserva tive. Single-fibre experiments may pave the way for more realistic est imates of angle-ply laminate strengths. These indicate that a simple o ne-third power rule can be used to estimate the potential strength. Ho wever, this is purely ad hoc at present, and needs to be put on a firm er footing through both theoretical and experimental studies. Furtherm ore, if this approach is adopted, edge effects will still have to be a llowed for, and estimated on the basis of the aspect ratio of the part . (C) 1997 Elsevier Science Limited.