Response of dynamically stressed material in sliding

Abstract

Sliding wear has been modelled on the basis of adhesive transfer as well as fatigue. In fatigue wear modelling it is assumed that the repetitive normal and tangential stressing is responsible for crack growth leading to final removal through fracture. The present work is aimed at clarifying the relative role of normal and tangential stresses on the removal process. A mild steel surface was subjected to cyclic compressive stress of 100 cycles s−1 by an electromagnetic exciter system. The compressive loading used was in the range from 22 to 4.5 N in each cycle. The stressing was done with a steel ball, resulting in concentrated contact. The stressing was done in both dry and lubricated conditions. Several spots stressed to different cycles were then subjected to one-pass sliding. Sliding experiments were conducted in dry and lubricated conditions with different normal loads. The fractional force changes with normal load and the removal process could thus be studied over a reasonable range of normal and tangential stresses. The emphasis in the study was on the lubricated contacts. The material removal in one pass and the corresponding stress conditions formed the basis for analysis. The number of stress cycles as well as the tractive stress have a significant influence on the removal process. Removal of material in lubricated sliding was attributed to fracture based on scanning electron microscope observation. Such fracture is a consequence of fatigue damage accumulated in normal cyclic stressing and hence implies that fatigue wear is a clear possibility in sliding. The relevance of this information to normal sliding wear is discussed.