Deformation and Strain Fields in Pin Specimens in Sliding Contact by Laser Speckle and Metallographic Techniques

Abstract

This paper describes the application of laser speckle photography to the measurement of deformations associated with sliding wear. The deformations and the associated strains are those which occur on the “side” of a rectangular-sectioned pin which is in sliding contact against a counterface disc. The side of the pin is exposed to a pulsed ruby laser beam, and a double exposure specklegram is made to record deformations which occur between laser pulses. Strain fields are obtained from displacement data by use of the Lagrangian description, and neglecting out-of-plane displacement gradients. By appropriately sequencing pulses, deformation histories can be obtained, in situ. And since the exposed side of the thin pin specimen represents the “cover” layer under which subsurface sections lie, the deformation history observable through the laser speckle method reflects the deformation behavior which is occurring on subsurface planes. By post-test metallography on planes close to this side face, the degree of correspondence between surface and subsurface deformation fields is demonstrated. The paper discusses the materials, apparatus and experimental techniques employed, and presents results obtained with several metallic specimens. Of particular interest is the extent of the plastically deformed subsurface zone, and its development as a function of time.