Friction measurement method and modeling of a metallic rod sliding through a flexible polymer tube

A new tribometer has been developed for the measurement of sliding friction between a stationary flexible polymeric sleeve and a rigid metallic rod that moves longitudinally within the sleeve. The tribometer enables both the normal and pull forces to be controlled and measured to high accuracy. The pull force was provided by an adaptation of a tensile testing machine which imparts a precisely controlled linear motion to the sliding tribopartner. Direct measurement of the normal force at the interface between the tribopartners is not necessary since it can be determined to very high accuracy by the innovative use of numerical simulation. Prior to its application to a specific physical situation, numerous replicate experiments were performed which demonstrated virtually perfect reproducibility. The tribometer was applied to determine the relationship between the extent of plasma processing of the bore of a flexible polymeric tube and the coefficient of friction between the tube and a stainless steel rod sliding within the silicone tube. This situation frequently arises in connection with therapeutic biomedical devices. The coefficients of friction determined from the experiments displayed a monotonic decrease as the extent of processing increased.