- 2015, CISM, Udine. Fiber reinforced composite materials provide a high level of structural safety against failure by tolerating damage (failure at microstructure level) while still sustaining significant loads. Using full load-bearing capacity of composite structures requires, however, reliable analysis of failure at micro and macro levels. The current failure theories, which are for homogenized composites, are unable to meet this requirement. This exposition reviews some of the commonly used theories to examine reasons for this limitation. Physical mechanisms underlying failure in composite materials are then discussed, motivating development of failure analysis with multi-scale approaches. Such approaches can also include effect of defects on failure. A comprehensive scheme is put forward for future development of physically based failure analysis of composite structures.