Strength critical composite structures are often designed with excessively large safety reserves. One key reason is due to the lack of a reliable failure theory; or more precisely, a consistent failure analysis methodology. This happens despite of the fact that advanced composites have been widely used in aerospace and other strength critical structures for nearly half a century.

    There are many contributing factors for the lack of a good failure theory because the internal constitutions of composites are complex, endowed with micron-scale entities materially and geometrically. But one uncanny factor is that the prevailing failure theories are mostly derived from a conceptual basis that is not consistently supported by physical evidences.

    In this short talk, the author will briefly outline the historical conceptual missteps taken and the resulting failure theories. A corrective measure is then suggested, along with some preliminary results. The latter seem to circumvent most of the short-comes inherent in the previous theories.

    The story being told in this talk could serve as a lesson learned, as new materials with nano-scale structures are being developed today. Indeed, a rational failure theory that span across dimensional scales in such materials will almost certainly be as elusive.