Optimal through-thickness temperature gradients for control of interlaminar stresses in composites

Abstract

Analytical solutions are sought for optimal temperature distributions to control the interlaminar stresses near the free edges of composite laminates subjected to uniaxial loading. Optimal through-thickness temperature gradients are obtained by minimizing appropriate performance indices that are functions of the far-field properties, with respect to the through-thickness temperature differences. Through the application of these temperatures, effects of local mismatches as well as global mismatches in two of the elastic properties, the Poisson's ratio and coefficient of mutual influence, are minimized. Numerical examples are given for several lay-ups made of graphite epoxy. It is shown that for a cross-or angle-ply laminate a uniform temperature rise or drop can completely eliminate all of the interlaminar stresses, whereas for other laminates nonuniform temperature distributions must be applied to minimize the stresses.

The Development of Thermal Stresses in Polyimide Matrix Composite Materials as a consequence of Three-dimensional Thermal Gradients – Analysis and Experiment

“…For example, in a cross-ply laminate, where the coefficients of thermal expansion depend also on ply orientation [8][9][10], the thermal stresses are estimated to be as high as the transverse strength [5,11], producing a reduction of strain to failure and developing transverse microcracks and delaminations [12][13][14][15]. Through-thickness thermal stresses affect material performance by influencing the fracture energy for delamination [16], fatigue life [15], in-plane and interlaminar shear properties [17][18][19][20] and peel stresses [21,22].…”