A technique to measure surface asperities plastic deformation and wear in rolling contact

Wear measurement of rolling contact during running-in is challenging because the mass loss is minor and the wear track change is almost undetectable. To overcome this limitation, wear is monitored by measuring the nano-scale deformation of the surface asperities of the roller in a rolling contact using the infinite focus microscope (IFM). An accurate surface image repositioning method is achieved between the initial profile and the subsequent profiles for each complete cycle. The image-processing technique for measuring the area and volume difference from the asperity profile is developed. Based on the constant volume principle, the volume attributed to the plastic flow is identified as the volume accumulated in the valley, and the wear volume is the difference between the volume of asperities removed and the volume of material accumulated in the valley. The wear volume measured using this technique can be as small as 514 µm3, which is equivalent to 4 nanograms of mass loss for stainless steel material. The plastic volume ratio is measured and the trend is in good agreement with the plasticity index, proving that this technique can be used to explain the plastic deformation and wear mechanism during the running-in phase of the rolling contact.