Experimental Observation of Slip Pulses During Onset of Sliding Friction

摘要

We present the experimental evidence of slip pulses prior to onset of sliding friction in quasistatic shearing of a bimaterial interface in laboratory experiments. Using two-dimensional block and slider configuration, we performed our sliding tests on polyurethane (PU)-poly(methyl methacrylate) (PMMA) material pair. Constant normal load (FN) of 114 N and sliding velocity (v_s) of 0.4 mm/s were chosen to induce stick-slip oscillations during sliding. Interface conditions were monitored using the techniques of photoelasticity and Digital Image Correlation (DIC) simultaneously. Sequence of 900 images before and after onset of sliding were acquired using high-speed photography at 44,000 frames/s. Isochromatic fringes show three distinct wave fronts passing along the interface from leading to trailing edge: (1) longitudinal wave, (2) shear wave, and (3) sub-shear wave. Analysis of grey-scale speckles using DIC, provided information on magnitude and direction of slip. Based on the wave and particle data, we conclude that longitudinal and shear waves produced negligible slip. Upon passage of slow sub-sonic wave front sliding ensued. Velocity of subsonic front was found to be around 30-85 m/s, while instantaneous slip velocities reached maximum values of 0.3 m/s. Our experiments clearly demonstrate the role of characteristic waves along the interface during sliding friction.