HR: 0830h
AN: NG41B-0058    [PDF]
TI: A Dynamic Model of Scratch Tests by a Conical Indenter and its Implication for Velocity-dependent Adhesive Friction --- An Interpretation of the Direct Effect of Dieterich-Ruina's Friction law ---
AU: * Yoshioka, N
EM: yoshi@yokohama-cu.ac.jp
AF: Yokohama City University, Seto 22-2, Kanazawaku, Yokohama, 236-0027 Japan
AB: It is a well known phenomenon in wear study that an indenter is in down-and-up motion at the beginning of a scratch process. A dynamic model was constructed to explain the motion of the indenter. The model assumes that a flow stress of indented material acts perpendicularly to the indenter surface and an adhesive friction also acts tangentially when the indenter is in motion. The movement of the indenter produces a groove on the indented material and a pile (ridges on both sides and a prow in front) is created around the indenter, the effect of which is taken into account in the model. We performed a series of scratch tests by a conical diamond indenter on aluminum, copper and brass surfaces with a constant horizontal velocity ranging from 0.1 to 1000 $\mu$m/s. The experimental result shows that the bulk friction force is proportional to the logarithm of the horizontal velocity. The comparison of the experimental results with the simulation by the model requires introducing a dynamic flow pressure $P_d$ for the indenter in motion. $P_d$ is estimated to be 1.2 - 1.3 times larger than the static flow pressure $P_s$ (which is obtained by a static indentation). It was found that the ratio $P_d/P_s$ plays an important role in scratch tests: the ratio determines the initial sinking angle and hence the overall locus of the indenter. Further we found that the velocity-dependent friction observed in the experiments must be attributed to the coefficient of adhesive friction $\mu$, which increases with velocity in a logarithmic manner. This fact suggests that the direct effect in the Dieterich-Ruina's constitutive friction law should be attributed to the velocity-dependent adhesive friction.
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 5194 Instruments and techniques
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting