Principal Measurement Inaccuracies of Pin-on-Disc Testers and Associated Mitigation Efforts

The Automated Universal Tribotester (AUT) is developed by the Institute of Dynamics and Vibrations (TU Braunschweig) and represents a reduced scale brake dynamometer. The setup is based on the pin-on-disc principle and the down-scaled test specimen are brought to contact to the disc and loaded via the specifically designed load unit. The AUT’s load unit is designed as a combination of parallel and serial leaf springs, resulting in a friction free motion. The stiffnesses in radial and tangential directions are much higher than in normal orientation. For the investigation of wear debris over time, changes in loads (e.g. forces, speeds, temperatures) are applied. Those varying loads result in tilting of the contact surface of the test specimen due to small elastic deformations. A change of the contact area is inevitable, and long time periods are needed to adopt the contact area to the new conditions. This prevents from investigating fast changes in the above mentioned loads. This paper gives an adaptive approach to address this problem. A passive optimization of the springs and the geometrical layout lead to improvements, but dynamic changes cannot be taken into account. This dynamic behavior results from variations of the procedure or the dynamic of the coefficient of friction itself, and their rate of change is obviously different. Therefore, an adaptive influence on tilting the AUT’s load unit is necessary. It is designed to have an additional degree of freedom, with actuators implemented in the modified mounting of the load unit.