<title>Defect-selective imaging of aerospace structures with elastic-wave-activated thermography</title>

Abstract

Aerospace structures are subjected to variable loads over long periods with rapid changes of conditions (e.g. humidity, temperature). Therefore the materials and components made out of them may suffer from aging and deterioration, especially since the weight of such structures is an important quantity. On the other hand, any failure of a component may cause costs that exceed by many orders of magnitude the cost of the component itself. On this background it is important to identify defects reliably and early enough during production or maintenance inspections in order to avoid catastrophic failure. This is the general and important task of nondestructive evaluation. We present a method where thermal effects are selectively activated in defects so that defects reveal themselves selectively even in the presence of complicated intact features. The mechanism involved is local friction or hysteresis which turns a variably loaded defect into a heat source which is identified by thermography. Loading is achieved by an elastic wave or oscillation with a suitable time dependence. The method is presented together with results obtained on aerospace structures.