The need for online microstructural image acquisition for tribological charecterisation in rolling/sliding contacts

Considering their tribological advantage, rolling/sliding contacts like gears, cams and rollers have adopted polymer-metal pairs in several engineering and domestic applications (copy machine, toys, pumps, etc.). The tribological behaviour of these applications is generally studied using real components or by standardized tribotests (ASTM). Although closer to the real application, investigations using real components are less effective because of the dynamicity involved in transfer layer, wear process, micro and macro slip characteristics and also due to the complexity in the contact geometry. In the current research, a twin-disc model representing the Hertzian line contact replicates the micro-slip whereas the macro-slip of the tribological system is achieved using different slip ratios. Efforts are made for microstructural characteristic through online imaging of contact surface to explore interaction between the mating surface and the dynamic behavior from transfer layer deposition. A computer vision system was developed for acquiring online micrographs of contact surface where a high-speed camera in concurrence with a microscope is used. Wear tests were conducted using polymer-metal pairs for offline and online investigations. Micrographs of the composite contact surface were acquired online at 7000 fps U+2013 35000 fps. Transition of wear mechanisms observed during the course of wear elucidates the interaction level at different stages of wear. From the view point of wear mechanism a clear distinction between run-in (ploughing) and steady state (adhesion and plastic deformation) was observed. The online micrograph of contact surface at different intervals validates the back transfer of polymer to the parent material. The unsteady stage is dominated by abrasion on the other hand, as the wear proceeds a transition to adhesion occurs. The initially unfilled (rough) steel surface without transfer layers gains advantage from the asperity geometry to plough the polymer surface. However, after gaining transfer layer in the steel surface, adhesion becomes the dominant mechanism. Finally, a combination of adhesion and abrasion is evident due to the dynamic behavior of transfer layer. Thus online computer vision is an effective tool to characterize the stages of wear process and to understand the mechanism underneath. Understanding the mechanism in a parametric way gives a chance to make necessary alterations for effective design of tribological system. However, the adhesion coefficient between transfer layer and the polymer-steel pairs has to be validated.

ISBN:9789036534536

Publication year:2013

Accessibility:Closed