Damage tolerant design
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A structure which has been constructed with Damage tolerant design is able to retain its integrity in the presence of damage due to causes such as fatigue, corrosion, manufacturing flaws, or impact. The goal of damage tolerant design is to provide adequate residual strength to allow safe operation until the damage can be detected and the component can be replaced or repaired. The application of fracture mechanics allows the scheduling of inspections based upon the initial size of a flaw, the probability of detection, and the rate of growth under operating loads.
The term is generally applied to structures rather than systems (in contrast to fault-tolerant, which more usually applies to systems)
Damage tolerance is a fundamental consideration in structural engineering. For instance, in the design of a safety-critical dockside crane, all the components in the primary load path are designed with a significant factor of safety in structural stress, over the most extreme load cases expected in combination, and with the material in the worst condition it is likely to experience over the design life.
Another example is the construction of a building in an earthquake prone area. The structure should be designed so that should damage occur, the structure will fail in a progressive way. Rather than the structure remaining undamaged up to a threshold, and suddenly collapsing completely and catastrophically, the structure will begin to fail as the threshold is exceeded, but will retain some integrity and possibly provide some protection to its inhabitants
Considerations in damage tolerant design: Generous factors of safety; Multiple load-paths; Progressive failure modes (rather than sudden failure); Comprehensive load case consideration: Allowances made for corrosion, material condition, previous damage.
