Deformation Features and Models of [±45]2s Cross-Ply Fiber-Reinforced Plastics in Tension

Series of experiments on [+/- 45](2s) cross-ply carbon-fiber-reinforced plastic specimens were carried out in tension with various loading programs. In analyzing stress-strains relations, the material was considered homogeneous. The total axial strain is presented as the sum of instantaneous residual (irreversible), nonlinear reversible, irreversible creep, and reversible creep strains. To separate the last two components, the hypothesis that their rates at different instants of time are different is used. Together with a generalized Kachanov hypothesis, this allowed us first to obtain equations for increments of only the viscoelastic strain. Further, equations in which only the viscoplastic strain is unknown are written, and only then the secant elastic modulus is determined. Questions of the choice of relations for describing strain components and the problem on identification of parameters of the relations are considered. Experimental data and results of their processing are presented, and they testify to the acceptability of the assumptions used and the efficiency of the approaches proposed.