Improving NDE (Non-Destructive Evaluation) Capability through Multiple Inspection with Application to Gas Turbine Engine Disks

摘要

Techniques are not capable of repeatedly producing correct indications when applied to flaws of the same length. As a result, the probability of detection (POD) for all cracks of a given length has been used to define the capability of a particular NDE system in a given environment. Thus the NDE reliability consists of two types of errors. For safety-critical components in airframe structures, Type I error is of major concern. According to the damage tolerant requirement, the inspection limit or the reset crack size should be the crack length associated with a 90% detection probability and 95% confidence level. On the other hand the main criterion used for analysis of the retirement-for-cause of gas turbine engine components is the minimization of the life cycle cost. The objectives of this report are to: (1) formulate and derive mathematically the resulting POD curve for multiple inspection systems; (2) investigate quantitatively the benefit and advantage of multiple inspection procedures; (3) establish the direction in which the NDE capability should be improved under certain mission requirements; (4) establish the strategy and sequence for multiple inspection procedures to reduce either Type I or Type II errors or both; (5) determine the POD curve for a disk from the POD curve of an NDE system; (6)determine the inspection reliability of engine disks; and (7) evaluate the benefit of multiple inspections for engine disks.