Wear debris of friction materials for linear standing-wave ultrasonic motors: Theory and experiments

Abstract

This study focuses on the wear debris of different friction materials for linear standing-wave ultrasonic motors (SWUMs). Wear debris with different morphology and sizes derive from wear mechanisms and has a critical influence on the contact state. The generation mechanisms of the wear debris are analyzed by using the elastic-plastic indentation mechanics and the typical morphography of the wear debris are discussed by considering of the energy balance. Oxide ceramics with high strength and fracture toughness were used as the friction materials of the driving tips, which are in contact with the carbon steel and oxide ceramic sliders. The wear tests were conducted using a homemade reciprocating apparatus. The worn surfaces and debris of different couples were investigated by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The statistical results of the debris size analysis were consistent with the results of the theoretical analysis of the indentation fracture mechanics. The wear debris was characterized with regard to size parameters, roundness factor, aspect ratio, and fractal dimension using image processing, and the relationships of the parameters and the wear modes are discussed. The generation mechanisms of the wear debris differ for the different friction couples due to the complex states and the differences in the mechanical properties. The plastic factor (E/H) and brittleness factor (H/KIC) are critical to the maximum dimension of the wear debris for given friction couples.