WEAR AND WEAR TRANSITION MODELING OF CERAMICS

Wear and wear transitions are the major concerns regarding the tribolo gical application of ceramic materials. The objective of this study is to understand wear and wear transition mechanisms of ceramics with em phasis on wear and wear transition prediction. There are four new find ings from this research. First, the critical external damage stress (s igma(D)) from a fracture mechanics model was modified to predict wear transitions for ceramics and was able to account for the effects of gr ain size and internal residual stresses on wear transitions. Then, the tensile stress at the rear edge of the contact was found as the predo minant stress which causes the ceramics to crack and leads to the subs equent wear transitions. The ratio of the maximum tensile stress (sigm a(max)) and the critical external damage stress (sigma(D)) was found t o be the critical parameter controlling wear transitions. Thirdly, a t echnique of ball sliding on inclined plane was developed for the appro ximation of the critical external damage stress for ceramics. Finally, a predictive wear model was developed. The correlation of the model w ith the experimental data of alumina and silicon nitride shows encoura ging agreement. The distinctive features of this simplistic model are its ability to predict the wear transitions as well as estimate the we ar of the brittle materials.