THE EFFECT OF WIDTH ON THE MECHANICAL-PROPERTIES OF ANGLE-PLY LAMINATES

It has recently been shown that wide specimens of angle-ply laminates are much stronger than expected on the basis of the Tsai-Hill theory o r the maximum-stress theory. This paper extends the work to investigat e the effect of test specimen width on the strength of +/- 45 degrees balanced angle-ply laminates. In addition, the relative stiffness has been estimated from the crosshead movement, and the previous results f or stiffness of wide test specimens are re-examined. It is shown that specimen strength increases monotonically with specimen width. The sti ffness, on the other hand, is approximately constant up to a width of 30mm, and then increases. With respect to the strength, these results confirm that the earlier theories were relevant only to edge effects, and not to most real structures. The earlier stiffness results, togeth er with the present result, suggest that laminate theory for elastic c onstants may also be influenced by edge effects. It is shown that the earlier results fit the standard laminate equations only if the shear modulus of the laminae are IO GPa for glass-fibre and 30GPa for carbon -fibre laminates. If these results are verified, the way is open for m uch greater use of angle-ply laminates. They may be an order of magnit ude stiffer and stronger than expected. Results with filament-wound tu bes lend strong independent support to the work. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.