Thermographic approach for a rapid fatigue limit estimation of gears

Gear resistance is an important mechanical aspect to ensure the proper functioning of power transmission systems. It is well known that one of the most dangerous failures in gears refers to tooth root fillet cracks, generally caused by bending fatigue. Standards help engineers in the gear design phase by providing material resistance data arranged on the basis of chemical composition, manufacturing process and surface treatment. The execution of experimental campaigns involving bending fatigue tests can be approached through two classical methodologies: meshing gears (MG) and Single Tooth Bending Fatigue (STBF) test approaches. However, it is important to note that both approaches necessitate a significant amount of time and effort. In this work, the STBF approach was adopted in combination with a Thermographic monitoring. This way, a full superficial acquisition of the tooth root thermal emission was performed during the fatigue test at different loads. So, the fatigue limit was estimated by an iterative analysis of thermal parameters evolution (Two Curves Method, TCM). The proposed Thermographic approach (TCM), already well-established in the literature for classical samples, allowed in this work to obtain fatigue limit data in the specific case of gears. Gears made of C45 and 20MnCr5 with surface treatments as induction hardening and case hardening respectively were tested. The obtained results in terms of bending fatigue limit values were compared with those evaluated by using consolidated approaches as the Staircase Method and with the indications available in ISO 6336 Standard for that material.