Stiffness and Strength Predictions of Discontinuous Fiber Composites

Abstract

The overall goal of this study is to develop a numerical modeling approach that will ultimately lead to the certification of discontinuous fiber composites based on analysis and modest experimental verification. A discontinuous fiber composite (DFC) material system called HexMC is considered in this study. A stochastic (Monte Carlo-type) finite-element modeling approach called the Stochastic Laminate Analogy has been developed. During a typical analysis the DFC structure of interest is divided into regions called Random Laminate Volume Elements (RLVEs). A unique randomly-generated and non-symmetric stacking sequence is assigned to each RLVE. Experimentally-observed variations in the stiffness of a DFC part are then simulated by performing many FE analyses, where a new random stacking sequence is generated for each RLVE during each analysis. Fracture predictions are obtained through a damage accumulation model called the ply discount scheme. Final structural failure of the part is declared when all plies within a single element have failed. Other definitions of final structural failure are also explored in this study. A typical analysis predicts that ply failures (i.e., “damage”) will evolve in a distributed manner throughout a typical DFC structure, even in the presence of stress risers. This damage pattern is in qualitative agreement with experimental observation. Analyses of un-notched and notched tension coupon specimens are discussed in this paper, and predicted B-basis and B-Max measures of modulus and strengths are presented.