Effects of preloading on brittle solids

A general theory that addresses the preloading effects on the strength of b rittle solids as a consequence of the progressive cracking is developed wit hin the framework of continuum damage mechanics theories. To accommodate th e effects of rotation of the loading paths in the stress-strain behavior of the material, an effective damage parameter is defined. The rate of the da mage parameter is obtained from the consistency condition of the loading (d amage) surface. Based on the directionality of the loading paths, damage is stored in appropriate directions through the components of material compli ance. The compliance and inelastic strain tensors are separated into tensil e and compressive components to address the material behavior in damage mod es I and II, respectively. Due to the lack of experimental data that assess the effects of orthogonal preloading, the model is compared with failure s imulations published by the University of Colorado. Stiffness recovery upon load reversal, an important feature of brittle solids, is modeled by intro ducing an effective compliance tensor in mode I. Finally, to demonstrate th e model's ability to replicate both proportional and nonproportional stress paths, it is compared against the experimental data.