1635. The Impact of Accomodating Defects on the Efficiency of Aircraft Design

Paper

Abstract

The design of aircraft metallic structure has become highly refined in recent years based on detailed structural modeling and the science of fracture mechanics. A similar understanding and prediction of damage accumulation in composites lags that of metals by many years. Yet we find ourselves rapidly entering the next design era, where composite material will comprise perhaps half of an aircraft’s structural weight. The industry stands, once again, at ‘compromise-crossroad’ – trading off inherent damage tolerance of materials and structural forms versus NDE limitations. Attempts are now being made by users to specify ‘design-to’ defects for composite structures. Cost-effective NDE techniques with suitable inspection speed and resolution for both initial fabrication and field checks are needed to avoid arbitrarily stringent design specifications which would result in conservative design practices. The requirements for NDE, however, must be balanced against advancements in damage tolerant materials and design to achieve maximum progress in the full utilization of composite capabilities.
A history of the evolution of damage tolerance criteria for metals as related to the B-58, F-111, and B-58 programs is presented followed by a discussion of the yet-to-be resolved damage tolerance issues for composite structure.