Inelastic behavior of an AS4/PEEK composite under combined transverse compression and shear. Part II: Modeling

micromechanical model is presented for simulating the nonlinearities exhibited by AS4/PEEK composites in shear and transverse compression, their interaction, and their rate dependence at room temperature. The fibers are assumed to be transversely isotropic and to be distributed in a hexagonal pattern in the matrix. The PEEK matrix is modeled as an elastic-powerlaw viscoplastic, isotropic solid through two related models. Model I is the simple J(2)-type viscoplasticity; Model II is a rate dependent version of the non-associative Drucker-Prager model. Both models are calibrated so that they reproduce the shear response of the composite. Model II is also calibrated to its transverse compression response. Both models capture the rate dependence of the composite well. Model I is significantly less stiff in transverse compression than the experimental data. However, it does a reasonable job of predicting other aspects of the biaxial experiments and captures the important trends of behavior observed. Model II does better in transverse compression, but shearing in the presence of transverse compression is found to be stiffer than the measured responses. The unit cell model allows us to examine the stresses in the composite, providing an explanation for the lack of interaction between the constant stress and the increasing stress observed experimentally for certain loading paths. (C) 1999 Elsevier Science Ltd. All rights reserved.