Analysis of crack propagation in stainless steel by comparing acoustic emissions and infrared thermography data

The aim of this work is to provide, in a non-destructive way, information about the structural integrity of materials subjected to a sinusoidal fatigue loading. In particular, the crack propagation was studied in AISI 430F/1 by using Acoustic Emission (AE) and Infrared Thermography (IT) at the same time. The main advantages of both approaches refer to the possibility to monitor the whole history of the specimen; in fact, differently by ultrasound inspection, no scanning is required and moreover the measurement is simplified by the fact that access from just one side of the specimen is sufficient. For AE technique two sensors were placed on the surface of the specimen in order to detect the elastic waves emitted by the material under stress and due to the activation of inner defects. By analyzing the overall acoustic signals it is possible to correlate a part of them directly to the crack propagation phenomenon. At the same time a thermocamera was placed in front of the specimen to live monitor the variation of surface temperature. Above all, the rise of temperature around the crack tip was observed in order to evaluate the advancing of the crack during the test. Finally a comparison between the two techniques was carried out aiming to assess the capability of each approach in following the evolution of the damage process.