Dynamic Behaviors of Contact Surfaces in the Sliding Friction of a Soft Material

It is known that detachment waves are generated on the surface of a soft material when it is slid on a hard surface under certain conditions. In the present study, the variation in the contact area that arises when a plate of a cross-linked polymer, poly-dimethylsiloxane (PDMS), is slid in contact with a glass hemisphere has been measured every 2 ms using a microscope and high-speed camera. The measurements elucidate that the behavior of the PDMS surface under sliding friction is divided into three modes. In mode I, a detachment wave is generated and it propagates across the contact zone. In mode II, a detachment wave is generated but does not propagate perfectly. In mode III, no detachment waves are generated. The Young modulus and load control the generation of detachment waves, but the contribution of the former is approximately 8 orders of magnitude larger than that of the latter.