Phenomenological constitutive modeling of the non-linear loading-unloading response of UD fiber-reinforced polymers

Abstract

The matrix-dominated mechanical response of a unidirectional carbon/epoxy system is studied through experiments and constitutive modeling. Experiments were performed on off-axis specimens to characterize the main factors controlling material’s diverse response under different loading conditions, and to measure the irreversible deformations occurring along the potential yield plane. Assuming that shear bands are precursors of ply cracks, and keeping in mind the physical characteristics of the material, a simple constitutive relation is offered to describe the plastic strain evolution and appearance of hysteresis behavior during loading and unloading. The latter is done by introducing a third component of strain, which was found to have a correlation with the level of plastic deformations the material has experienced. The proposed framework is able to reproduce the nonlinear monotonic and loading–unloading response of fiber-reinforced polymers under tension and compression, while taking into account the effects of multiaxial loading and different shear behaviors in longitudinal and transverse directions. This paper presents a broad perspective on the main factors controlling the material nonlinearity within a simple constitutive model, nevertheless, the model predictions show good agreement with experimental data.