Composite Laminates with Negative Through-the-Thickness Poisson's Ratios

A simple analysis using two-dimensional lamination theory combined with the ap propriate three-dimensional anisotropic constitutive equation is presented to show some rather surprising results for the range of values of the through-the-thickness ef fective poisson's ratio v xz for angle-ply laminates. Results for graphite-epoxy show that the through-the-thickness effective poisson's ratio can range from a high of 0.49 for a [90] laminate to a low of -0.21 for a [±25] S laminate. It is shown that negative values of v xz are also possible for other laminates.