Advancing the Techniques of Thermoleastic Fracture Mechanics of Composite Materials

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CMS 9713356 PI: John A. Nairn University of Utah New techniques for solving fracture problems in composites that treat the residual stresses commonly arising in composite materials by using thermoelastic fracture mechanics formulations are developed using a four-pronged approach: the derivation of new exact thermoelastic fracture analyses specific for composites; the development of approximate techniques including variational fracture mechanics, the analysis of observed finite fracture events, and experimental verification. The exact techniques provide new tools for analysis of composite fracture and are used in place of stress intensity factor techniques, which are powerful for isotropic and homogeneous materials, but are much less useful for composites. The approximate techniques are aimed at finding general tools for accurately determining the quantities appearing in the exact analyses. These techniques will be based on new variational theorems that will make it possible to derive useful upper and lower bounds for energy release rate. The term "finite fracture events" refers to the observation that composites often fail by a series of discrete fracture events (e.g., fiber fracture, ply cracking, or debonding) rather than by continuous crack growth. The present work develops fracture mechanics tools for dealing with such discrete fracture events. All analysis methods are verified by application to real and relevant failure processes in composite materials.