Analytical modeling of the interaction of an ultrasonic wave with a rough bone-implant interface

Experimental investigation on ball plate contact using ultrasonic reflectometry: From static to dynamic

Machine elements such as rolling element bearings are widely used in engineering and transportation areas. The life of a bearing is closely related to the stress state in the constituent components. Determining the stress state experimentally is difficult since the contact region is hidden inside the contacting bodies, making it difficult to characterize without altering the contact itself. This paper presents an experimental study to monitor static and dynamic ball-on-flat contacts, by using an ultrasonic reflectometry measuring technique, to demonstrate the concept of monitoring operating ball-bearing conditions in a non-invasive manner. By using an ultrasonic focusing probe and a 64-element ultrasonic array, contacts between a nitrile ball and a Perspex plate as well as contact between a steel ball and a grooved steel plate were characterised under both static and dynamic conditions. Both contact size and distribution of contact stress can be visualized in 2-dimensional plots. In this paper, the capability of ultrasonic reflectometry for non-invasive characterisation of contact conditions are demonstrated, and more importantly the development of multiple measuring mechanisms to realize real-time contact monitoring from static to dynamic conditions is illustrated. The proposed technique in the study is expected to characterise dynamic contacts of bearings in various scenarios from small mechanical systems (e.g., micro motors) to large civil infrastructures (e.g., wind turbines).

Acoustic Scattering Models from Rough Surfaces: A Brief Review and Recent Advances

This paper proposes a brief review of acoustic wave scattering models from rough surfaces. This review is intended to provide an up-to-date survey of the analytical approximate or semi-analytical methods that are encountered in acoustic scattering from random rough surfaces. Thus, this review focuses only on the scattering of acoustic waves and does not deal with the transmission through a rough interface of waves within a solid material. The main used approximations are classified here into two types: the two historical approximations (Kirchhoff approximation and the perturbation theory) and some sound propagation models more suitable for grazing observation angles on rough surfaces, such as the small slope approximation, the integral equation method and the parabolic equation. The use of the existing approximations in the scientific literature and their validity are highlighted. Rough surfaces with Gaussian height distribution are usually considered in the models hypotheses. Rather few comparisons between models and measurements have been found in the literature. Some new criteria have been recently determined for the validity of the Kirchhoff approximation, which is one of the most used models, owing to its implementation simplicity.