Tooth Root Fatigue Fracture: a Comparison Between Pulsator and Running Gear Tests

Critical industries such as aerospace, wind power and automotive pose the industrial demand for gears with increasingly higher performances; hence, improving the power density of gearboxes. Over the years, numerous materials and treatments have been developed to improve the gear strength. This development phase must be supported by appropriate testing activities aiming to quantifies the effect of such treatments. Hence, obtaining data that can be used in a later design phase of the whole geared transmission. In this context, pulsator tests (also known as Single Tooth Bending Fatigue (STBF) tests) are used as endurance tests designed to characterize the bending fatigue strength of the tooth root. These tests are equivalent tests: the tooth root is in fact loaded not by meshing with another gear but, more simply, by applying a pulsating load on the tooth flank via a testing machine. The lack of meshing leads to both statistical and fatigue differences, making the elaboration of the experimental evidence a mandatory step before using it in the design phase. This work focuses on the analysis of the experimental evidence per se and its comparison with the scenario of running gear tests, where gears mesh under load. Firstly, it presents the current state of the art, characterized by a specific historical perspective. Secondly, it shows the current research, in which local approaches, applied to the tooth root, are used to compare the two cases.