The demands made on structural composite materials in modern design are increasingly stringent. Greater performance, lower costs, increased reliability and safety all require that the design engineer knows more and more of the material systems available. Bringing together new knowledge contained in constitutive models of continuum design and empirical information from a girth of experience is proving to be difficult because the number of service and process variables required for sophisticated, optimal design is becoming increasingly larger. Understanding Structural Integrity (SI) provides the key to the successful design, certification, and safety of large composite structures and engineering composite materials. This is because SI analysis treats simultaneously the design, the materials used, figures out how best components and parts are joined, and takes service duty into account. But predicting precisely where a crack will develop in a material under stress and exactly when in time catastrophic failure of the structure will occur remains an unsolved mystery.