4. Stress Concentration Evaluation of a Plate with Symmetrical U-Notches Under Tensile Load Using TSA and a Lepton IR Camera

It has already been showed that Thermoelastic Stress Analysis (TSA) may be employed as an extremely useful technique in structural integrity assessment applications. Recent developments in the microbolometer technology made possible the commercial offer of very low-cost infrared cameras, one of these being the FLIR Lepton 3.5. Use of such low-cost cameras associated with commercially available software or in-house developed algorithms makes possible to localize anomalies and to determine quantitative results on the stress distribution acting on nominal and hot-spot locations in loaded structures. A further step will widely disseminate IR temperature and TSA measurements and consequent analyses into a powerful low-cost health monitoring tool. The aim of the present work is to demonstrate the use of this experimental technique in the evaluation of the stress concentration caused by a U-notch in a plate under tension load using TSA and a Lepton camera. A MATLAB in-house algorithm was developed for post-processing the measured IR signal. The achieved stress-distribution and stress-concentration results are also compared with those generated by measurement systems that integrate a commercially available software coupled to the FLIR Lepton 3.5 and to a median-cost FLIR A655sc IR camera. Moreover, the paper shows that the low-cost camera can be used in the monitoring of fatigue crack growth as well as in the determination of stress intensity factors for cracks initiated and propagated from the U-notch.