The Effect of Stacking Sequence on Thickness Scaling of Tests on Open Hole Tensile Composite Specimens

The effect of ply stacking sequence on the open hole tensile strength of composite laminates has been investigated both numerically and experimentally. A finite element technique has been developed which includes the sub-critical damage within and between the plies. It is thus able to capture in some detail the effects of variation in stacking sequence. All possible permutations of 0, 90 and ± 45 ° plies in a quasi-isotropic layup have been analysed. Variations in strength have been observed and explained in terms of sub-critical damage development. Two stacking sequences of interest were chosen for scaling in the thickness direction by increasing the ply thickness. The first showed a significant decrease in strength and a change in failure mode from fibre dominated to delamination dominated failure with increasing thickness. The second showed no such decrease in strength or change of failure mode. Both of these stacking sequences were tested experimentally at both thicknesses and excellent agreement with the numerical models was obtained, both in terms of damage mode and failure stress.

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