Effect of Microcracks on the Thermal Expansion of Composite Laminates

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Abstract
A finite element analysis was used to quantitatively predict the effect of matrix microcracks in the 90° plies of graphite/epoxy composites on the coefficient of ther mal expansion in the 0° direction, α y (perpendicular to the cracks). Results were generated for [0 m/90n]s, [0/±45/90]s and [0/90/±45] s graphite/epoxy laminate con figurations. Analytical predictions were compared with experimental results for the two quasi-isotropic laminate configurations. Both analytical and experimental results showed that microcracks reduced the effective stiffness of the 90° plies, thus causing the laminates, thermal response to be more like that of a [0] laminate. The change in αy was a function of lamina material properties, microcrack density, fiber orientation, and stacking sequence. A combination of classical lamination theory and finite element analysis was used to predict the effect of microcracks in both the 90° and 0° plies. Analytical results showed that the addition of microcracks in the 0° plies do affect αy, but to a lesser extent than those in the 90° plies.