Contact pressure evaluation in mechanical structures focusing on instantaneous frequency of ultrasonic pulse.

Abstract

There are many contact interfaces in machines. Some contact interfaces including lubricants exist in engines and gear boxes, and they often are sliding interfaces. Contact pressure on the interfaces strongly affects machine performance. This study proposes a novel evaluation method for the contact pressure by using ultrasonic pulses. Interferences of the ultrasonic pulses which are multiply reflected on the contact interfaces are affected by thickness of gap of the contact interface, which is a thin lubricant layer in this case. The proposed method can inform us that there is spatial unevenness of their thickness on the contact area because observed interference of the pulses is sensitive to the thickness and the contact pressure. We demonstrated this method to evaluate an axial contact pressure of a roller bearing. Comparing experimental results and simulation results at 4 sampling points, it was estimated that the thickness of the lubricant layers and the contact pressure are uneven on the roller bearing. The range between the thickest lubricant layer and the thinnest lubricant layer was about 3 μm.