Inductance-based sensing of surface roughness, with application to wear sensing

This paper reports a new nondestructive noncontact method of sensing surface roughness, particularly the surface undulation produced in the plowing stage of wear. This method involves inductance measurement. It is fast, provides global information and is suitable for real-time monitoring, but it is limited to electrical conductors. This amounts to structural self-sensing. Ultramild abrasive wear primarily in the plowing regime, with areal weight loss ≤ 0.075 g/cm² and ≤ 0.040 g/cm² for steel and aluminum, respectively (i.e., thickness loss ≤ 0.30 mm and ≤ 0.48 mm for steel and aluminum, respectively), is effectively sensed by this method. The inductance measurement involves two electrical contacts (clips) and an LCR meter (2 kHz). The inductance increases monotonically with increasing degree of wear primarily in the plowing regime, beyond which it does not increase further. This is due to the sensitivity of the inductance to the surface undulation, as expected from Faraday’s law. Longitudinal wear (wear performed in the inductance measurement direction, i.e., direction along the metal bar length) and transverse wear (wear performed along the direction perpendicular to the inductance measurement direction) give similar weight loss. However, the fractional increase in inductance due to wear is greater for transverse wear than longitudinal wear, as expected from Faraday’s law. Hence, the inductance method can discern the surface undulation direction, i.e., the wear direction, but the weight loss method cannot. The fractional increase in inductance due to wear is greater for steel (magnetic) than aluminum (not magnetic). However, magnetic character is not required for the sensing.