A STUDY OF THE BENDING MECHANICS OF ELASTIC MEMORY COMPOSITES

Elastic Memory Composite (EMC) materials are fully cured, fiber-reinforced composites with a thermoset shape-memory-polymer matrix. The unique properties of the matrix enable EMC materials to achieve high packaging strains without damage. At temperatures above the glass transition temperature of the resin, Tg, the material exhibits a dramatically reduced compression stiffness due to significant softening of the resin and poor lateral stabilization (and microbuckling) of the fibers. Conversely, the material’s tensile stiffness remains relatively unchanged at temperatures above Tg. Thus under bending, there is a dramatic variance in material stiffness through the laminate’s thickness, which gives rise to a nonlinear bending response. The present paper describes a study to analytically predict this nonlinear bending behavior. Specifically, the paper presents: 1) an analytical solution for the nonlinear bending response of an EMC component resulting from bilinear constitutive behavior due to fiber microbuckling, 2) an analytical solution for the strain at which microbuckling is initiated, 3) verification of the analytical solution with results from a finite element analysis that incorporates a user defined subroutine for the material’s bilinear constitutive behavior, and 4) a correlation of the analytical results with experimental data. The main conclusion of the present work is that a relatively simple bilinear constitutive law leads to predictions of nonlinear bending response that are similar to the behavior seen in bending experiments on EMC laminates.