Active Thermography for residual stresses identification in gears by using different heating sources

The application of Non-Destructive Techniques (NDTs) in mechanical research is becoming significant since there is a growing demand for non-invasive research methodologies that also consider the environmental impact. An innovative configuration of Thermography, called Active Thermography (AT), meets this demand and is already used in industrial areas to investigate defects within the material. Recent studies have also explored the potentialities of AT in other mechanical fields such as material characterisation or damage investigation, extending its applicability to other industrial research fields. The aim of this work is to expand the application of AT in the field of surface treatment analysis. In particular, an alternative Non-Destructive approach based on AT was proposed for the identification of residual stresses by means of thermal responses, and the thermal results obtained with two different heating sources are presented and compared with classical X‑Ray residual stress measurements. A laser and a lamp were used to generate localised and distributed heating over the surface of the investigated specimens. Dedicated data elaboration procedures and thermal indexes were proposed for the surface treatment identification based on the heating source adopted during the Active Thermography tests. The results are illustrated for samples and gears, made of 20MnCr5 steel, subjected to carburizing and shot peening surface treatments. A detailed analysis of both mechanical and physical properties was also carried out to verify the AT results.