Wear of ceramics due to thermal stress: a thermal severity parameter

Wear of ceramics under dry sliding conditions is, besides mechanical overlo ad, often governed by frictional heating. On the basis of this study a new thermal severity parameter is introduced and applied to an existing wear ma p as a function of mechanical and thermal loading introduced by Adachi et a l. [Wear 203/204 (1997) 291]. The new map is valid for a wide range of mate rial properties and operating conditions. In this paper, a method is presen ted to predict the boundary between the mild wear regime and the severe wea r regime due to frictional heating. To obtain this, the work of Bos [Fricti onal heating of tribological contacts, Ph.D. Tbesis, University of Twente, Enschede, The Netherlands, 1995] was used to calculate contact temperatures . This model is essentially a fit on numerical calculations, making it poss ible to include heat partitioning between dissimilar materials while retain ing closed form expressions, The stress resulting from the contact temperat ure can be compared with material properties to obtain the thermal severity of a contact. A new dimensionless thermal severity number, TS, is introduc ed to determine the thermal severity of a contact. The model has been exper imentally justified using measurements of pins of different materials slidi ng against two types of tetragonal zirconia polycrystal discs. In these exp eriments it was observed that if the specific wear rate exceeds the value o f 3 x 10(-6) mm(3)/N m, the sliding surfaces were rough and the wear was re garded as, severe. This criterion is closely related to the criterion based on the ratio of process surface roughness over mean grain size Adachi et a l. [Wear 203/204 (1997) 291]. (C) 2001 Elsevier Science B.V. All rights res erved.