Optical and ultrasound local contact measurements of dry friction interface under vibration

Abstract

Friction joints are widely used in machine design to allow an easy assembly of different components. The joints have the added benefit of providing damping to the structure due to frictional energy dissipation at the interface, which can reduce vibration amplitude and hence improve performance and life of the machine. The nonlinear nature of a friction joint can introduce a significant challenge when predicting the dynamic response of the system and the lifetime of the parts. The prediction of the global dynamic response is relatively accurate today due to the development of different contact models and advance nonlinear solvers, but predicting and measuring the local contact condition inside the joints accurately still represents a major challenge. The latter is of highest importance when trying to accurately represent a joint for accurate nonlinear dynamic predictions, and when trying to predict wear inside the interface.

The main aim of this PhD project is to develop approaches that allow the monitoring of the contact interface of friction joints during a vibration cycle and improve the understanding of the contact mechanics at the interface. Initially a comparison of full-field optical measurements and ultrasound measurements on transparent PMMA specimens is used to obtain understanding of the link between the contact mechanics at the interface and the ultrasound signal. A clear link between the optically measured real area of contact and the sliding conditions could be established, which is then linked to the ultrasound signal. This understanding is then used for the interpretation of the ultrasound signal of steel specimens. The ultrasound technique shows the capability to identify sticking, microslip and gross slip stages in one sliding cycle in a steel to steel contact, providing for the first time high quality validation of the local contact condition for explicit nonlinear dynamic models.