Evaluation of standard life assessment procedures and life extension methodologies for fracture-critical components

Endeavors to maximize the safe service lives of aeroengine components have led to a variety of life assessment methodologies. The following are reviewed in the paper: Life-to-first-crack, Databank Lifing, Damage Tolerance and Damage Mechanism based procedures. Their service implementation involves a variety of aspects of which the following are briefly discussed: stress analysis, defects and component life extension methods. Building on several of the concepts discussed, a lifing methodology based on risk regulation of inspection is then introduced. By varying the inspection intervals over time, the number of inspections can be minimized while ensuring that the risk of a failure does not exceed an acceptable level. Given inspection, it is shown that the actual safe service life of a component can be more strongly determined by the probability of crack detection than by the minimum detectable crack size.