Rheological Measurements and Adhesion

Abstract

THE work described by Dr. E. W. J. Mardles¹ may be considered in relation to our results on yield stresses in lubricating greases², which were determined under conditions of simple tangential shear. We presented evidence to show that at shearing stresses above a certain value (termed the 'first yield stress') flow of grease takes place by slip on a thin film of oil at the grease–solid interface. Flow as a result of breakdown of the bulk grease structure occurs only above a certain higher stress, which is the yield value commonly measured and is called by us the 'second yield stress'.