Energetic approach based on IRT to assess plastic behaviour in CT specimens

In this work, the Thermographic technique (IRT) was used to characterize the fracture mechanics behaviour of stainless steels. In particular, IRT is proposed for evaluating the dissipated energy and the plastic area around the crack tip in order to study the fatigue crack growth. Experimental approaches used for the measure of dissipated energy require an accurate equipment and suitable techniques that may restrict the applications just to laboratory tests. The proposed approach is based on thermal signal investigation in the frequency domain in order to separate the two heat sources related to the material behaviour during fracture mechanics test: thermoelastic sources and intrinsic dissipations. These latter are directly related to the plastic phenomena around the crack tip and occur at the twice of the loading frequency. Both amplitude and phase signals at the twice of the loading frequency can be used for evaluating the crack growth rate. In particular, the first index through an estimation of the heat dissipated while the second due to the effects occurring at the crack tip. It was also demonstrated as the proposed approach is capable of monitoring the crack growth over time and in automatic way by means of such the contactless and full field technique.