Analysis of contact pressure using ultrasonic reflection

This paper describes a study of the possibility of using ultrasound to measure the pressure between two surfaces in contact. Engineering surfaces are rough, and when they are pressed together, intimate contact is made at the tips of the asperities. The higher the contact pressure the closer the conformity between the surfaces. Lf a wave of ultrasound is incident at an interface, it will pass through the contact regions and be reflected back at the air gaps. The proportion reflected is found to be related to the stiffness of the interface via a 'spring model'. The measurement of reflection has been used to study the nature of the contact between aluminium rough surfaces pressed together. A numerical model of elastic rough surface contact has been used to interpret stiffness data and to determine a reflection/contact pressure calibration. The model gives good qualitative agreement and a reasonable quantitative agreement given the assumptions inherent in its formulation. At this moment in time, the authors have shown that ultrasound may be reliably used to determine the geometrical extent of a contact region, and can give useful qualitative information about the distribution of pressure across an interface.