Study of guided wave propagation on a plate between two solid bodies with imperfect contact conditions

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).

Modeling and numerical study of the influence of imperfect interface properties on the reflection coefficient for isotropic multilayered structures

The microelectronics industry is expressing an increased demand for the development of non-destructive tools and methods for health control and diagnostics in multilayered structures. The purpose of these tools is to detect problems such as delaminations, inclusions and microcracks. The aim of this paper is to study the effect of imperfect interfaces on the wave propagation in multilayered structures. This type of structure represents the typical architecture of many microelectronic components. This study will be based on the calculation of the reflection coefficient and the guided waves dispersion curves. The investigated structure is an isotropic trilayer where two metallic layers are bonded together by an adhesive layer made of an epoxy resin. Comparisons were performed in order to evaluate numerically the influence of several properties of the adhesive layer on the guided waves behavior. In addition, an imperfect viscoelastic interface layer model [1] has been implemented in order to simulate different adherence qualities between the metallic layers.

Quantification of Bolt Tension by Surface Acoustic Waves: An Experimentally Verified Simulation Study

Quantifying bolt tension and ensuring that bolts are appropriately tightened for large-scale civil infrastructures are crucial. This study investigated the feasibility of employing the surface acoustic wave (SAW) for quantifying the bolt tension via finite element modeling. The central hypothesis is that the real area of contact in a bolted joint increases as the tension or preload is increased, causing an acoustical signature change. The experimentally verified 3-D simulations were carried out in two steps: A preload was first applied to the bolt body to simulate the realistic behavior of bolted joint; and the SAW propagation was then excited on the top surface of the plate to reflect from the bolted joint. The bolt tension value was varied between 4 and 24 kN (properly tightened bolt) in the steps of 4 kN to study the effect of the bolt tension. The results indicate an increased reflected wave amplitude and a gradual phase shift, up to 0.5 µs, as the bolt tension increased. Furthermore, the result shows that the distance between the first reflected wave and the source becomes shorter as the preload increases, as hypothesized. A 1.9 mm difference in the distance between the maximum and minimum preload was observed. As part of this study, the simulation results were also compared with the experimental results, and a good agreement between the simulation and experiments was demonstrated.