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

Vibration transmissibility measurement of glove materials under different grip forces

The transmission of vibration from tools, through work gloves and into the hands, is affected by many factors such as glove material properties, tool vibration conditions, temperature, and grip force. This study investigated how glove material properties affect tool vibration transmission into the index finger. Three samples of material (two taken from differently designed anti-vibration gloves and another for comparison that was designed for mounting vibration-sensitive equipment) were assessed using stepped sinusoidal vertical vibration excitations covering a range of a one-third octave band (from 20 to 400 Hz). Twelve human subjects were used for the testing. For all samples and subjects, measurements were obtained for: (I) dynamic mechanical analysis (DMA) of the samples; (II) the transmissibility of vibration to the index finger at a grip force of 30 N, across the range of frequencies; and (III) transmissibility of vibration to the index finger at a frequency of 125 Hz for finger grip forces of 15, 30, and 45 N. No significant vibration attenuation was provided at frequencies below 150 Hz. The two materials taken from the gloves that passed the ISO 10819:1996 test showed resonance at frequencies of 150 and 160 Hz a, but the material that did not pass the ISO test showed resonance at 250 Hz. The attenuation for all three materials was occurred at 400 Hz. There was no significant change of transmissibility across the range of finger grip forces for any of the material samples. The level of transmissibility was found to vary between samples and subjects

An evaluation of shoe tread parameters using FEM

Within this paper, a three-dimensional finite element (FE) model of a uniformly loaded, single rubber block, is described and run using loading conditions replicative of a standard slip resistant footwear test. The FE model considers rubber hyperelastic and viscoelastic material properties, obtained using dynamic mechanical analysis. The performance of the FE model was evaluated through analytical compression analysis and experimental contact area testing. The effect of tread grooves was investigated with relation to slip-resistance during walking. Analysis and discussion are provided of the tread model's sliding contact areas, contact pressure, stress, and front edge mechanics

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

Retro-fit particle dampers for panels in space structures

The presented paper explores the use of discrete particle dampers (PDs) as a retro-fit solution for vibration control of structural panels in space structures. The damper enables the user to change the structures overall dynamical characteristics thanks to their inherent many tuning parameters such as particle volume fraction, individual particle size, and overall mass. damper can provide broadband control and can operate at a range of amplitudes and within a range of severe environments. Random and sine vibrations of varying amplitudes, up to 1kHz, are applied to investigate the change in resonant and damping behaviour from the PDs for both bending and torsion modes. A finite element model (FEM) was then used to determine the estimated damping through a first order Modal Kinetic Energy method. The experimental and FEM results were found to satisfactorily agree with each other. It was found that optimised PDs can contribute high levels of energy dissipation with damping ratios up to 10%. At the same time, providing an acceptable mass contribution making them not only an acceptable candidate for space structures, but also a retrofittable option with minimal re-qualification by test