OVERVIEW

Design of composite structures has damage tolerance as its major challenge, which means that design criteria are location dependent. Modern designs should address the challenge separately for each Principal Structural Element, PSE. The concept of PSE is accepted in aerospace practices and regulations and serves well as a basis for developing different damage scenarios. The term PSE defines a principal structural segment, the failure of which would result in loss of the vehicle. It turns out that the pursuit of damage tolerant designs will involve residual strength, damage growth rates, damage resistance and fail-safety. It will also be shown how damage tolerance becomes the cornerstone of Structural Safety.

Considering that both established practices and regulations require structural integrity with manufacturing flaws, accidental damage and effects of discrete source events (e.g. bird-strikes) present, it is not surprising that damage tolerance becomes the last bulwark of safety. A safe structural design of a PSE must be based on a realistic assessment of practical damage scenarios. Scenarios that involve definition of threat, initial damage, detectability, damage growth and type of inspection must be part of both design process and design criteria. This chapter contains a cavalcade of possibilities and a display of typical and necessary orders of magnitudes.

Damage tolerance (except for the discrete source events) integrity requires that a limit load capability be maintained during the life of the vehicle. Limit load is defined as "the largest load expected in service," and it turns out for composites that damage tolerance requirements...