Parameter identification problem in one-parameter plasticity model for fibrous composites

This investigation is concerned with optimal identification of the parameters in Sun–Chen’s plasticity model. An improved off-axis tensile test scheme involving only two angles is proposed. The model’s feasibility is assessed with a combined mathematical and mechanical analysis. In mathematical identification of a minimum of two angles, explicit derivation of the goodness of a power-law fitting on effective stress–plastic strain curves via least square theory was imperative. In mechanical analysis to identify the optimal angles, coupling between the resolved shear and transverse stresses in the evolutions of plastic deformation is investigated; the angle that generates a maximal plastic flow is calculated. In addition, a sensitivity analysis of identified parameters with the fiber’s nominal angle errors is performed and the result is presented via an insensitivity path. Specimens from carbon/epoxy systems were utilized in the experimental program. Results confirm that the predictions of shear and off-axis nonlinear stress–strain responses based on the improved scheme (15° and 45°) proposed in this investigation demonstrate comparable accuracy to those based on Sun–Chen’s common scheme.