Influence of roughness-dependent interface contact behavior on vibration characteristics of blade with under platform dampers

This study investigated the nonlinear vibration of blades with under-platform dampers (UPDs), explicitly incorporating the effect of contact interface roughness. A novel dynamic analysis method was developed, where the rough interface is represented by a statistical ensemble of asperities following a Gaussian distribution. Based on this representation, the nonlinear normal contact force was derived from probabilistic contact mechanics, and the tangential force was modeled using Coulomb friction. These forces were integrated into a few-degree-of-freedom blade model formulated via the Assumed Mode Method (AMM), with the blade simplified as a lumped-mass beam. The model was validated through frequency-sweep tests on a dedicated rig, which also serve to identify the structural damping ratio. A parametric study quantitatively evaluated the influence of preload, excitation force, contact angle, and surface roughness on UPD performance. Key findings indicate that optimal damping requires higher preload at increased excitation levels, and that smaller contact angles promote vibration suppression by maintaining a friction-dominated regime. Crucially, neglecting surface roughness is shown to lead to a significant overestimation of damping performance. Therefore, the design of both blades and UPDs must comprehensively account for surface treatment (roughness), the preload-excitation interplay, and contact angle.