Plasma deposition of constrained layer damping coatings

Plasma techniques are used to generate constrained layer damping (CLD) coatings on metallic substrates. The process involves the deposition of relatively thick, hard ceramic layers on to soft polymeric damping materials while maintaining the integrity of both layers. Reactive plasma sputter-deposition from an aluminium alloy target is used to deposit alumina layers, with Young's modulus in the range 77-220GPa and thickness up to 335 μ, on top of a silicone film. This methodology is also used to deposit a 40 μ alumina layer on a conventional viscoelastic damping film to produce an integral damping coating. Plasma CLD systems are shown to give at least 50 per cent more damping than equivalent metal-foil-based treatments. Numerical methods for rapid prediction of the performance of such coatings are discussed and validated by comparison with experimental results

The development of a new artificial model of a finger for assessing transmitted vibrations.

Prolonged exposure of the hand to tool-induced vibrations is associated with the occurrence of conditions such as vibration white finger. This study involves the development of a new artificial model that approximates both loading and vibration behaviour of the human finger. The layered system uses polypropylene "bones", encased in a cylinder of low modulus, room-temperature curing silicone gel (to replicate subcutaneous tissues), with an outer layer of latex (to replicate the dermis and epidermis). A protocol for manufacture was developed and dynamic mechanical analysis was carried out on a range of gels in order to choose a range close to the mechanical properties of the human finger. The load-deflection behaviour under quasi-static loading was obtained using an indenter. The indentation measurements were then compared with a set of validation data obtained from human participant testing under the same conditions. A 2-D FE model of the finger was also used to assess vibration responses using existing parameters for a human finger and those obtained from the tested materials. Vibration analysis was conducted under swept sinusoidal excitations ranging from 10 to 400Hz whilst the FE finger model was pressed 6mm toward the handle. Results were found to compare well. This synthetic test-bed and protocol can now be used in future experiments for assessing finger-transmitted vibrations. For instance, it can aid in assessing anti-vibration glove materials without the need for human subjects and provide consistent control of test parameters such as grip force

Modelling of nonlinear dampers under low-amplitude vibration

Particle dampers can suppress structural vibration over a broad range of frequencies, which makes them attractive in comparison to many other passive damping technologies. They constitute a cavity filled with particles. Energy dissipation from particle dampers depends on many parameters including, size of the cavity, diameter of the particles, shape of the damper, filling ratio, material properties of the particles and the volumetric ratio between the cavity and particles. Performance changes with the amplitude of the excitation and, to a lesser extent, the frequency. This study focuses on the energy dissipation in the granular material that fills particle dampers as the damper is subjected to low-amplitude dynamic load. The behaviour of this material is modelled using the Discrete Element Method (DEM) for a specific case: a tube-shaped cavity filled with spherical particles. An equivalent continuum model is proposed for the granular material and the Finite Element Method (FEM) is used to simulate the response of a damper subject to structural vibration. This study shows how the equivalent material model can be used to predict amplitude dependent behaviour in particle dampers under lowamplitude excitation