Defining the Envelope for Sonic IR: Detection Limits and Damage Limits

摘要

Work is presented which begins to define the envelope of applicability for the sonic IR NDE technique. Detection limits define the faintest flaw signal that can be perceived, which is a function of flaw size and depth, excitation strength and duration, and the detector limits (spatial, temporal, thermal). A unique contribution of the present work is the development of a model to predict the dynamic frictional heating of a crack, and this is combined with a transient heat transfer analysis to define the detection limits. Damage limits consider the risk of damage to a part from the application of the dynamic excitation. Experience has shown that the dynamic excitation can damage parts, notably for brittle materials such as ceramics with existing flaws. Since sonic IR is intended to be nondestructive it is important to test parts in a manner consistent with preserving the part integrity. The evaluation of damage limits assumes that additional part damage during testing is a fatigue process that propagates existing cracks. Paris' law for fatigue damage is employed to provide an estimate of fatigue crack propagation during the dynamic forcing. Both detection limits and damage limits are combined to create an envelope of applicability for sonic IR.