Fatigue damage propagation in AISI 430 F/1: A monitoring approach based on acoustic emission and infrared thermography

This paper presents a review of the results obtained by studying crack propagation in AISI 430F/1 by using Acoustic Emission (AE) and Infrared Thermography (IT) at the same time. Both the techniques share the capability to allow continuous monitoring during the entire life of the specimen; in fact, differently by other non-destructive techniques (i.e., ultrasound), the acquisition does not require scanning. To implement AE technique two sensors were placed on the surface of the specimen to detect the elastic waves generated by the activation of the defects inside the material subjected to stress. Several features of the recorded acoustic signal were analyzed in order to correlate their variation with the crack propagation process. Data were analyzed also applying different kinds of post-processing filters in order to isolate, for example, only events occurring near the slots of the sample or characterized by a given level of amplitude. Appropriate filtering of the cumulative graph of the hits was observed to display a behavior that can be correlated with different stages of propagation of the crack. Interestingly the amplitude analysis of the emitted signal shows the presence of the principal bands of amplitude. Furthermore a thermocamera was set-up to get information connected with temperature variation of the specimen under test. Local rise in the temperature about the crack tip was used to follow crack evolution during the test. Finally, a comparison between the two techniques was carried out aiming to assess differences between the two approaches in following the damage evolution.