Guidelines to use input contact parameters for nonlinear dynamic analysis of jointed structures: Results of a round robin test

Turbomachinery and other jointed structures are carefully designed to optimise their dynamic response and prevent unwanted high-cycle fatigue failures due to vibration. Advanced numerical models are employed to predict the often nonlinear dynamic responses, but their reliability is partially limited by the lack of understanding of the friction mechanisms between the vibrating contact interfaces. Although several high-frequency friction rigs have been developed at different institutions to measure contact parameters such as friction coefficient and contact stiffness, a lack of direct comparisons prevents a throughout understanding. To address this issue, a comparison of these contact parameters has been performed by employing the high-frequency friction rigs of Imperial College London and Politecnico di Torino. A test plan was designed to cover a wide experimental space by testing the friction rigs to their limits and measuring hysteresis loops under a range of normal loads and displacement amplitudes at room temperature. Measurements from the two very different experimental setups are compared, showing a good level of agreement for the friction coefficient, but also highlighting some differences, especially for the contact stiffness. New insights are provided into the physics of these contact parameters and specific guidelines are given to improve contact models used for nonlinear dynamic analysis.