ON FRICTION-INDUCED TEMPERATURES OF RUBBING METALLIC PAIRS WITH TEMPERATURE-DEPENDENT THERMAL-PROPERTIES

This paper investigates the temperature rises for dry sliding systems when the variation in the thermal conductivity with temperature is tak en into account. For the purpose of the analysis, it has been assumed that the thermal conductivity of the rubbing materials vary linearly w ith temperature. Accordingly, materials are classified into three cate gories based on that variation: materials for which the conductivity d rop with temperature elevation (class a); materials for which the cond uctivity increases with temperature elevation (class b); and materials for which the conductivity-temperature curve has an inflation point ( class c). The variable conductivity temperatures are obtained by apply ing the so called 'Kirchoff transformation' to the fundamental solutio n of the heat equation. The results indicate that the behavior of the conductivity with temperature is significantly influential to the magn itude of the temperatures reached by the rubbing pair. For a variety o f sliding pairs analyzed in this work, significant variation between t he constant and the variable conductivity predictions were found. For example, the temperature rise for a mild steel (AISI 1020) rubbing pai r, sliding at 6 m/s and 30 N nominal load, predicted by the variable c onductivity solution is about 30% higher than that predicted using a c onstant conductivity solution. It is also shown that the estimates of the heat conducted through the surface may be in error (by about 30-40 %) if based on a constant conductivity solution. Such behavior has dir ect effects on the thickness of the thermally affected subsurface laye r (the so-called thermal skin), and the thermal distortion of the cont act interface. The error introduced in the estimates of the temperatur e rises for class c materials is shown to be proportional to the ratio between the inflation to the melting temperatures of the moving solid . (C) 1998 Elsevier Science S.A. All rights reserved.