Damage Tolerance Analysis
In ensuring the continued safe operation of the damage tolerant structure, inspection schedules are devised. This schedule is based on many criteria, including:
- assumed initial damaged condition of the structure
- stresses in the structure (both fatigue and operational maximum stresses) that cause crack growth from the damaged condition
- geometry of the material which intensifies or reduces the stresses on the crack tip
- ability of the material to withstand cracking due to stresses in the expected environment
- largest crack size that the structure can endure before catastrophic failure
- likelihood that a particular inspection method will reveal a crack
- acceptable level of risk that a certain structure will be completely failed
- expected duration after manufacture until a detectable crack will form
- assumption of failure in adjacent components which may have the effect of changing stresses in the structure of interest
These factors affect how long the structure may operate normally in the damaged condition before one or more inspection intervals has the opportunity to discover the damaged state and effect a repair. The interval between inspections must be selected with a certain minimum safety, and also must balance the expense of the inspections, the weight penalty of lowering fatigue stresses, and the opportunity costs associated with a structure being out of service for maintenance.
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