Experimental Study of a Creeping Polymer Sphere in Contact With a Rigid Flat

The creep of a polymer sphere contacting a rigid flat under a constant normal load is investigated experimentally. An optical technique is used to observe in situ the evolution of the contact area while the increase of contact interference is measured simultaneously. The experimental results obtained with PTFE spheres of different diameters pressed against a sapphire flat under different normal loads are presented and the effect of sphere diameter and normal load on the creep of the contact parameters is discussed. The present experimental study validate recently published theoretical results of a contact model for a creeping sphere and a rigid flat showing that a universal similarity solution exists for the dimensionless creep interference and dimensionless creep contact area as functions of the dimensionless time.