Micromechanics models for the elastic constants and failure strengths of plain weave composites

Various types of matrix dominated failures in polymer matrix composites (PMC) are reviewed. Current methods to evaluate the modulus degradation of PMC materials are discussed including viscoelastic/plastic and continuum damage models. It is pointed out that in each case the approach is based upon developing an analytical constitutive relation for the material in order to represent a measured stress-strain response. The suggestion is made that care must be used in the measurement of stress-strain behavior such that the modeling represents the true material behavior. New digital imaging methods are suggested as a means to determine in situ properties at a local scale commensurate with the continuum modeling procedure. A little used method to model viscoelastic/plastic (linear and non-linear) effects is discussed and modified to obtain a simple and easy to use time dependent failure law. Also, a little used energy based time dependent failure criterion is presented which can be combined with a non-linear viscoelastic integral approach to provide a prediction method for the time for creep rupture under simple stress states. Each is validated with experimental data for simple stress states but their generality is such that they could be used for complex (3-D) stress states. Advantages and limitations of both are addressed. Finally, a discussion of possible fruitful research areas are presented with the view of providing engineers in industry with an easy to use accelerated life prediction procedure.