Off-Axis Inelastic Behavior of Unidirectional AS4/PEEK at High Temperature and Its Micromechanical Analysis.

Abstract

Nonlinear stress-strain behavior of a unidirectional carbon fiber-reinforced composite AS4/PEEK under various off-axis loading conditions at high temperature was examined with particular emphases on the rate and loading-mode dependence of the response. Monotonic tensile stress-strain curves at high temperature accompanied marked nonlinearity for all off-axis angles except θ=0○.Permanent strains were clearly observed for all kinds of off-axis specimens after unloading. The off-axis permanent strain remaining after unloading became larger as the applied maximum stress increased. The strain and stress rates have appreciable influences on the flow stress of the off-axis nonlinear stress-strain relationships. These observations indicate that the off-axis nonlinear deformation of this composite involved an irrecoverable inelastic part and it was characterized by a viscoplastic deformation mechanism. In view of these experimental results, a simple micromechanics model for predicting the off-axis rate-dependent nonlinear stress-strain behavior of unidirectional AS4/PEEK was developed using the Aboudi's cell method for homogenizing composite behavior and the Chaboche's viscoplastic constitutive model for describing the rate-dependent inelastic behavior of the matrix material. The primitive calculations using the micromechanics model developed favorably reproduced the off-axis rate-dependent nonlinear behavior for the unidirectional AS4/PEEK at high temperature.