Transverse cracking and elastic properties reduction in hygrothermal aged cross-ply laminates

The changes in the mechanical properties as a result of multiple transverse cracking in the hygrothermal aged cross-ply laminates are examined theoretically. Most authors have studied transverse matrix cracking in cross-ply lay-ups and used the longitudinal Young's modulus as an indicator of the extent of damage development. Reductions of typically only a few percent have been found at saturation crack spacing. Some authors have studied the effect of matrix cracking on Poisson's ratio. The results show large reductions at saturation transverse cracking. In this work the degradation of the longitudinal and the transverse properties of the hygrothermal aged cross-ply laminates due to transverse matrix cracking under longitudinal tension was studied. First, the material properties of the composite are affected by the variation of temperature and moisture, and are based on a micro-mechanical model of laminates. Consequently, the hygrothermal conditions degrade the stiffness of the laminate. This degradation is taken into account to assess the changes in Poisson's ratio and longitudinal modulus due to transverse cracking.