WEAR PROCESSES DURING FRICTIONAL SLIDING OF ROCK - A THEORETICAL AND EXPERIMENTAL-STUDY

An experimental study of frictional wear of rock, conducted with a rot ary apparatus, shows that wear loss, the loss of material from the int erface of two bodies during frictional sliding, is a function of norma l stress and the initial roughness of the sliding surface. Under a giv en normal stress and initial roughness, the wear loss-sliding displace ment relationship indicates that wear rate is initially high and then gradually decreases to a constant value. The wear process results in a n evolution of the surface topography as shown from profilometer measu rements of the surface at different stages of wear. The distribution o f asperity heights shows that the top of the sliding surface is progre ssively truncated with accumulated slip. Based on a model of two rough surfaces in elastic contact, a numerical model for wear can describe wear in two different stages: a transient stage and a steady state sta ge. In the transient stage, the wear mechanism is interpreted as shear ing off of interlocking asperities. The total contribution by this mec hanism is proportional to the overlapping volume of the asperities, V , which is related to the initial roughness as well as the normal stre ss. In the steady state stage, wear is almost linear with displacement and the wear rate is proportional to the real area of contact between the two rough surfaces. Introducing a parameter h, the interlocking d istance between two contacting asperities, provides a better understan ding of the wear process with different surface roughnesses. Below a c ritical value of interlocking distance h(c), the contacting asperities deform elastically and slide over each other. When h > k(c), they ten d to shear off. The model predicts the effects of normal stress and in itial roughness, and its predictions are in good agreement with the ex perimental results.