Stress relaxation response of active fiber composites

The mechanical and physical properties of materials change with time which can be due to the viscoelastic effect and/or due to hostile environmental conditions and electromagnetic fields. An experimental study on active fiber composites (AFCs) having PZT5A fibers dispersed in epoxy shows that the mechanical response of AFC depends on time, temperature, and mechanical loading. We examine the time-dependent response of the AFC, where the polymer constituent undergoes pronounced viscoelastic deformations at different temperatures and mechanical loadings. A micromechanical model is used for predicting effective time-dependent response in active fiber composites with thermal, electrical, and mechanical coupling effects. The micromechanical model is derived based on a simplified unit-cell model in which limited information on the local field variables in the fiber and matrix constituents can be incorporated in predicting overall performance of active composites. We compare the overall stress relaxation response of the active composites determined from the micromechanical model with those from available experimental data. We found that the viscoelastic behavior of the matrix constituent can significantly influence the electro-mechanical coupling response of the AFC and elevated temperatures accelerate the relaxation process of the epoxy matrix and the AFCs.