On the relevance of a microslip contact model for under-platform dampers

A crucial part of building reliable models for the design of under-platform dampers for turbine blades resides in the appropriate description of the contact conditions, both in the normal and in the tangential direction. The aim of this paper is to determine to what extent microslip due to the combined non-linearities along the normal and the tangent of non-conforming contact surfaces influence the damper behaviour. The ultimate goal is to determine whether introducing these features in the contact model would improve the performance of numerical routines used at the blade-damper design stage. In order to explore this problem, a purposely developed contact model is tuned on a single-contact test and then included in the numerical model of a curved-flat damper to simulate its cylindrical interface. The damper numerical routine is then validated against the results from an experimental device purposely developed to test the dynamics of a damper loaded between moving platforms. It is shown that the validated numerical routine featuring the newly introduced contact model predicts, in comparison with the standard contact model (where partial slip and normal approach non-linearity are not considered), a lower dissipated energy by an amount that would not be justifiable to neglect.