Combined experimental methods to assess the fatigue limit

Purpose of this paper is to perform an energetic analysis on metal specimens under fatigue testing using the simultaneous application of different non-destructive techniques: thermography (TH), acoustic emission (AE) and digital image correlation (DIC). They assure the better evaluation, being contactless methods, usable in real time and, even if TH and DIC are related to the specimen surface, representative of the inside state of the materials. In particular, the cascade of hits and the acoustic energy were recorded to assess the parameters linked to the fracture of the materials. At the same time, the surface temperature, detected by a thermocamera, and the displacements induced on the specimen, using the DIC on the free zone of the specimens, were recorded. The DIC analysis allows the evaluation of the correct displacement by a pattern realized on the opposite face respect to TH. AE data and hysteresis curves (derived by DIC) were compared with the measures acquired by TH and reveal a reliable correlation between them in terms of fatigue limit.