Rate-dependent microplane triad model for high strain rate behavior of woven composites

A strain rate-dependent microplane triad model (MTM) is presented here for the high strain rate behavior of woven composites. The previously developed MTM is enhanced with formulations for various strain rate-dependent phenomena, formulated at the constituent level. These include matrix visco-elasto-plasticity and the rate-dependent strength, failure strain, and dynamic fracture energy of the fibers and the matrix. Two alternate rate scaling formulations are incorporated to capture the range of experimentally observed behaviors: (i) type I scaling, in which strength, strain at peak, and fracture energy increase with strain rate, and (ii) type II scaling, in which strength increases while strain at peak and fracture energy decrease. By introducing rate effects at the constituent level, the model gains a more mechanistic and physically consistent basis. The anisotropic strain-rate dependence observed at both the representative unit cell (RUC) and coupon scales emerges naturally through micromechanical homogenization within the microplane triad framework. The various model parameters for quasi-static and dynamic behavior are systematically identified at the RUC (material point) scale using reverse calibration from experimental data. The constituent-level structure of the formulation enables a streamlined, sequential calibration process, in which parameters are uniquely identifiable without ad-hoc tuning. The calibrated model is then applied to simulate coupon-level responses under tension and shear for plain and twill weave composites. Results demonstrate excellent agreement with experiments across loading modes and strain rates. The simulations capture both classes of rate-dependent behavior, including increases in peak stress and hardening, as well as either an increase or decrease in strain-to-failure. The model further captures the rate-dependent evolution of biaxial strength envelopes, including the changing interaction between normal and shear stress components. The rate-dependent changes in failure patterns and degree of damage localization are also captured well. These findings demonstrate the predictive capability of the microplane triad approach across scales and loading conditions. The constituent-based rate formulation makes the approach readily adaptable to other classes of textile composites.