Inference of Fatigue Crack Closure Stresses from Ultrasonic Transmission Measurements
The nondestructive determination of stress is usually attempted by measuring stress (or strain) related changes in material properties. Included are direct x-ray measurements of lattice constants and indirect inferences of stress or strain from changes in ultrasonic velocities or magnetic properties. However, in problems in which one wishes to determine localized stresses across an interface between two materials, neither approach is satisfactory. X-rays typically measure surface stresses and do not sample the stress condition near an internal interface. Ultrasonic velocity measurements and magnetic measurements can sense interior conditions, but also average over the properties of the intervening material. Hence, they cannot determine the localized stresses at the interface without sophisticated data reduction techniques such as those employed in holographic reconstructions.
KeywordsFatigue Crack Crack Closure Ultrasonic Velocity Closure Stress Ultrasonic Transmission
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