A Modified Kinematic-Hardening Viscoplasticity Model for Off-Axis Creep Behavior of Unidirectional CFRPs at High Temperature

Abstract

A macromechanics constitutive model to describe the anisotropic creep behavior of unidirectional composites under off-axis loading conditions is developed with a particular emphasis on accurate prediction of temporal creep softening due to stress variation. A viscoplasticity model that takes account of a combined isotropic and kinematic hardening is adopted as a base for this formulation, and the evolution equation of the kinematic hardening variable is elaborated to enhance the accuracy of prediction of the transient creep softening due to stress variation. Validity of the modified kinematic-hardening viscoplasticity model is evaluated by comparing with the experimental results on unidirectional T800H/3631 carbon/epoxy composites. It is demonstrated that the proposed model can adequately describe the off-axis creep behavior of the unidirectional CFRP laminate under constant and variable stress conditions.