In Situ Measurement of Contact Area and Pressure Distribution in Machine Elements

In machine element design it is important to know the size and pressure distribution of the contacts between components. Ultrasound will reflect back from the interfaces between these machined parts. This phenomenon has been investigated with a view to determining its suitability for contact measurements. An ultrasonic transducer, which both emits and receives pulses, is scanned across the interface. The reflected pulses are recorded and used to build up a map of the contact. Experiments have been performed to produce these reflection maps for simple point contacts. An analytical model was used to determine the stiffness of the interface from these measurements and a calibration procedure performed to predict contact pressures. The resolution of the method is relatively coarse and this results in some finite blurring of Hertz-type contacts. Numerical deconvolution procedures have been used to improve the accuracy of measured data. Two applications of this technique are presented. Measurements of the contacts within a universal joint demonstrate that for small concentrated contacts it is difficult to obtain more than qualitative information. But, for the large interface between the bush and shaft in an interference fit, measurements of the interfacial pressure are much more feasible.