Abstract : Fiber-reinforced polymers (FRPs) composites consisting of a thermoset or thermoplastic polymer matrix reinforced by carbon, glass, or aramid fibers have been used as a substitute for more conventional materials in a wide range of applications, particularly in the aerospace, defense, and automobile industries. FRP strength-to-weight ratio and load-carrying capacity and toughness are superior to those of typical metals. Because of the widespread availability of measurement techniques, experimental testing of composite materials has largely outpaced the computational modeling ability of such complicated materials, forcing design of composite structures to follow a build-test-build cycle. The use of the extended finite-element method (XFEM) has revolutionized the design process: it improves modeling efficiency and allows investigation of failure mechanisms. The research documented in this report clearly demonstrates that the design of composite structures is no longer restricted by the time-consuming and costly build-test-build methodology. Specifically, this research demonstrates the ability of XFEM, combined with cohesive behavior, to model various modes of failure in composite materials simultaneously. These advancements in computational physics-based modeling are changing the manufacture of FRPs: comprehensive modeling techniques can significantly reduce the effort required to build and test future composite structures and will allow previously untested composite arrangements to be properly analyzed prior to any physical testing, vastly reducing cost and time requirements.