Dynamic strain measurements in a sliding microstructured contact

Abstract

A novel experiment is described which measures the tangential strain developmentacross the contact between a PDMS (polydimethylsiloxane) block and a glasssurface during the initial stages of sliding. The surface of the PDMS block hasbeen microfabricated to take the form of a regular array of pyramidal tips at20 µm separation. Tangential strain is measured by means of light scattering from the interfacebetween the block and surface. Three phases are observed in all experiments: initial sheardeformation of the whole PDMS block, a pre-sliding tangential compression of the tip arraywith stepwise increase of the compressive strain, and sliding in stick–slip movements asrevealed by periodic variation of the strain. The stick–slip sliding between the regular tiparray and the randomly rough counter surface always takes on the periodicity of the tiparray. The fast slip can cause either a sudden increase or a sudden decrease in compressivestrain.