Thermography Applied to the Study of Fatigue Crack Propagation in Polycarbonate

Abstract

Thermography was used to study the propagation of fatigue cracks during cyclic loading of pre-cracked SAE keyhole polycarbonate specimens. A micro-bolometer infrared camera (FLIR A655sc) and a commercially available software program (DeltaTherm2) were employed. The stress intensity factors were determined using a hybrid thermoelastic stress analysis (TSA) technique. The crack growth rate was determined via thermography using two different approaches. The first approach used the output of the crack-tip position from the developed TSA algorithm and the number of cycles between data sets. The second approach used temperature measurement as a new way to determine da/dN (crack growth rate) directly. As a result, da/dN vs ΔK (stress intensity factor range) graphs were plotted and fitted using Paris’ law. A comparison between the resultant da/dN vs ΔK curves and results found in the literature, as well as curves from the finite element method (FEM) simulations showed good agreement. The conclusion was that thermography is a very powerful tool that can detect, measure and monitor fatigue cracks in polycarbonate.