An experimental study has been conducted to study stiffness changes in laminates containing inclined (off-axis) plies. The class of laminates studied is glass-epoxy (0, ±θ4, 01/2)s with θ = 25, 40, 55 and 70. It is found that for θ > 40 multiple cracks occur in the θ-plies while for θ < 40 no cracks are found. However, for all θ angles the laminate moduli change. A continuum damage mechanics approach is used to calculate stiffness changes due to cracks. In the absence of cracks the shear modulus reduction in the θ-plies, determined from independent tests on a (±45)s laminate, is found to provide good prediction of the observed stiffness changes.

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