OVERVIEW

Design of safe damage tolerance critical composite structure involves the process of trading different features to produce a balanced result. For example we could be faced with a situation that requires consideration of, damage tolerance, damage resistance, controlled damage growth and detectability. Figure 7.1 presents a partial picture of the design challenge which includes basing the resulting structural properties on a selected inspection method, and Figure 7.2 shows the conditional distributions for residual strength for one choice of regions.

Figure 7.1: Design space.

Figure 7.2: Residual strength distributions.

Figure 7.1 is predicated on the use of damage regions 3 to 6 and the use of a minimum residual strength (allowables-like approach). The approach is described in Figure 7.2.

The situations after the inspection at ? are:

1. The structure is damaged, the damage is not detected and the structural integrity is lost, X _? H _? U _?; Reduce probability of occurring;

2. The structure is damaged, the damage is not detected and the structural integrity is preserved, X _? H _? U _?; Focus on the event of lost integrity at next inspection, X _? H _? U _? U _T, Control safety by controlling damage growth rates in design;

3. The structure is damaged, the damage is found, the structure is repaired, X _? H _? R _?; Focus on impact before next inspection, X _? H _? R _? Y _k U _T; Control safety by controlling damage resistance...