PUNCH CRUSH OF UNIDIRECTIONAL COMPOSITES AT SUB-MILLIMETER LENGTH SCALE: EXPERIMENTS AND SIMULATIONS

Abstract

An experimental methodology has been developed to fabricate unidirectional (UD) S-2 glass/epoxy composite films at sub-millimeter length scale, and to study the micromechanical punch crush damage mechanisms of UD ribbons of width 1mm (machined from sub-millimeter UD composite films) under transverse compression loading. Quasi-static micro-mechanical crush damage mechanisms includes: (i) fiber-matrix debonding, (ii) non-linear large-deformation of matrix resins, (iii) punch-shear of fibers, (iv) crush of fibers under diametric compression and (v) crush of matrix resins. Modeling these micro-mechanical damage mechanisms are challenging. Finite element (FE) models of UD composite ribbons of sub-millimeter thickness have been developed by modeling individual fibers through the thickness, fiber-matrix interface debonding with zero-thickness rate-dependent cohesive elements, transverse fibers fracture with stochastic zero-thickness cohesive elements, and fiber crush is modeled by erosion of elements. Micro punch crush experiments on UD S-2 glass composites show formation of a sheared plug which undergo through-thickness crush damage yielding about 1.4 GPa crush strength. Micromechanical 3D FE model can predict this crush damage mode at a matrix erosion strain of 0.99.