Ž . Wear 225–229 1999 1222–1237 Novel experimental techniques for investigating time resolved high speed friction S. Rajagopalan, M.A. Irfan, V. Prakash ) Department of Mechanical and Aerospace Engineering, Case Western ReserÕe UniÕersity, CleÕeland, OH 44106-7222, USA Abstract The paper presents some recent advances in experimental methods to investigate the phenomenon of high speed friction. In particular, Ž. Ž. two novel experimental methods are employed in the present study: a the plate impact pressure–shear friction experiment, and b the torsional Kolsky bar friction experiment. Using these experimental configurations, dynamic frictional characteristics of Carpentor Hampden tool-steelrTi6Al4V and Carpenter Hampden tool-steelr7075-T6 Al are investigated under conditions of high interfacial normal Ž . Ž . pressures 100 MPa to 2 GPa , high slip speeds 1 to 60 mrs and elevated temperatures. The results of these experiments provide some new insights into the role of the applied normal pressure, interfacial slip speeds, interfacial temperature, and the surface roughness in controlling the tribology of dry sliding interfaces. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Applied normal pressure; High speed friction; Interfacial slip speeds; Interfacial temperature 1. Introduction The nature of dynamic friction forces between two bodies in contact is a complex process and is affected by a long list of factors. Most experimental apparatus used to investigate dynamic friction lack the reproducibility of friction data. The results of these experiments are multi- branched friction versus slip velocity curves, which even for the same material and the same experimental apparatus depend not only on the properties of the frictional interface but also on the dynamic parameters of the apparatus such w x as mass, stiffness, and damping 1–4 . The present paper presents some recent advances in the experimental methods to investigate the phenomenon of dynamic friction. In particular, the present study is aimed towards understanding the dynamic frictional character- istics of sliding interfaces under relatively high interfacial Ž . Ž normal pressures 100 MPa to 2 GPa , high slip speeds 1 . to 60 mrs and elevated temperatures. Under these interfa- cial conditions the constitution of the material interface is essentially stable and all plastic deformation is confined to a very thin layer at the frictional interface. As a result, the frictional forces developed are expected to depend primar- ily on the applied normal pressures, slipping velocity, slip ) Corresponding author. Fax: q 1-216-3683007; E-mail: vxp18@po.cwru.edu distance, interfacial temperatures, and the surface rough- ness. This category of dynamic friction measurement en- compasses the area of interfacial friction commonly ob- served at the toolrdie work-piece interface in several conventional and non-conventional material removal andror material forming operations. Two novel experimental configurations are employed in Ž. the present investigation. These configurations are: a the Ž. plate impact pressure–shear friction experiment, and b the torsional Kolsky bar friction experiment, which is a modification of the conventional torsional Kolsky bar ap- paratus used for investigating the high strain rate behavior of engineering materials. These experimental configura- tions represent a significant improvement over the conven- tional dynamic friction experimental configurations by al- lowing the control of the interfacial tractions through the use of combined pressure–shear loading instead of manip- ulating actuator motion. Moreover, the use of pressure shear loading allows critical friction parameters such as the interfacial tractions, slip speed, and interfacial tempera- tures to be interpreted by measurements of stress and particle velocity at positions remote from the frictional interface. The interfacial conditions obtained in these experiments are schematically illustrated in Fig. 1. For the plate-impact pressure–shear friction experiment the normal pressures range from 0.5 to 2 GPa and slip speeds range from 1 to 0043-1648r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0043-1648 99 00071-X