Low cost infrared thermography for automated crack monitoring in fatigue testing

The potential of using infrared thermography in the assessment of crack-tip parameters is described. The use of microbolometers is studied specifically to establish their suitability for use in thermoelastic stress analysis (TSA) for establishing the crack-tip parameters and for automatically monitoring crack growth using temperature measurement. To compare the behaviour of the two types of infrared cameras a camera model is devised, which is used to predict the thermoelastic response. A new automatic crack growth monitoring approach is developed based on the temperature measurement from the raw thermal data collected using the microbolometer. The thermoelastic response model and the crack monitoring procedure are demonstrated on 316L stainless steel single edge notch tension (SENT) specimens. Cracks were established in the specimens, grown and monitored using both types of infrared detector. The procedure is validated using measurements from the photon detector and it is shown that accurate stress intensity factors (SIFs) can be obtained from growing cracks using directly the live readings from the microbolometer. The procedure provides a new means for non-contact measurements in fatigue testing, establishing crack growth rate and the SIFs with the potential for actuator control