Feasibility study on the use of tangled metal wire particles as the adjustable elements in tuned mass dampers

Tangled metal wire particles are a recent innovation that could provide an alternative to traditional damping materials. As they have low mass and are relatively insensitive to temperature, they are suitable for use in harsh environments. The present contribution demonstrates that these particles can be used as working elements for an adjustable Tuned Mass Damper. It is shown that the dynamic properties of a collection of tangled metal wire particles can be characterised with a reasonable accuracy, to provide the basis for a practical adjustable damper. The effectiveness of the new damper is demonstrated on two different vibration modes of a typical engineering structure. Finally, the new damper is shown to be much lighter than an equivalent tuned mass damper that was constructed more traditionally using polymeric O-rings

Damping of metallic wool with embedded rigid body motion amplifiers

The use of entangled metallic wires as vibrational dampers and shock isolators is of interest in a variety of applications. By taking advantage of the frictional contact between the contiguous wires, it has been shown that significant amounts of energy dissipation can be achieved. The amount of energy dissipation is highly dependent on many factors with one in particular being the excitation amplitude. When the excitation amplitude is low, a combination of the number of contact points, in which have relative motion, and the contact pressure are lessened often leading to a sacrifice in energy dissipation. In this paper, spherical metallic rigid bodies are embedded within metallic wool. These rigid bodies act as motion amplifiers in which, locally within the metallic wool, amplify the excitation amplitude leading to an increase in vibrational damping. Presented are experimental modal results from various metallic wool/embedded rigid body arrangements within a prismatic hollow aluminium tube. It is found that the incorporation of the embedded rigid bodies into the steel wool significantly improves the damping within the system. It is demonstrated that an increase in damping by 2328% has been achieved at only a 3.8% penalty in mass. It is found that the level of damping from the embedded rigid bodies depends not only on the excitation amplitude but their quantity and the accompanying steel wool configuration. A finite element procedure coupled with an analytical model is proposed which accounts for the strain energy produced within the steel wool to estimate the damping effect that this filler material has on the behaviour of the overall structure. The model treats the metallic wool/rigid sphere combination as a homogeneous equivalent solid with amplitude dependent damping properties, thereby reducing the complexities of the physics-based model while still providing an estimate of the vibrational damping while in the frequency domain

Mathematical and numerical evaluation of the damping behaviour for a multi-strand bar

Multi-strand systems include, but are not limited to, electrical wire conductors, structural cables, and some composite reinforcements. These systems (apart from composite reinforcements) are generally metallic for a variety of reasons. One often overlooked advantage is that dry friction between metal contacts can provide damping over significantly wider temperature ranges than is typical for common damping materials such as viscoelastic polymers. This paper, proposes a mathematical model that describes the hysteretic vibrational behaviour of a frictionally constrained multi-strand bar constructed from strands that have a circular cross-section. The mathematical model analytically predicts the frictional system stiffness under simply supported boundary conditions. The assembled strands are numerically simulated using finite elements and hysteresis behaviour is compared to that obtained from the mathematical model. This shows that the mathematical model is capable of predicting the stiffness and the force-displacement hysteresis response of the system for a variety of conditions

Characterisation of creep behaviour using the power law model in copper alloy

This paper presents a numerical strategy for the characterisation of the creep behaviour model of the copper alloy, which is widely used in aircraft applications under creep conditions. The high possibility of the material failing, while operating under load at an elevated temperature, has led to the important study of the creep lifetime prediction analysis, by presenting the Norton’s rule based on the Power-law model to describe the secondary creep behaviour of the material. In order to demonstrate the nature of the creep formulation, the SOL 400 modules from MSC Nastran 2014 are implemented in order to conduct the uniaxial tensile test in 2000 N of applied load and 473 K of temperature condition. As a result, the exponential curve is formed from the relationship of the creep strain rate and stress, with a 5.1% error based on the value of the stress exponent, n, between the simulation and experimental results and this was still be acceptable because it was relatively small due to the formulation in the simulation. Consequently, a relation of the creep rate curve can then be plotted with respect to the load steps and the variation patterns due to the stress factor also being discussed. Therefore, the results show a good agreement, which indicates the capability of this model to give an accurate and precise estimation of the secondary creep behaviour of the materials

Experimental investigation and modeling of dynamic performance of wave springs

This paper investigates vibration suppression potentials for a novel frictional system - a wave spring. Two different types of wave springs, crest-to-crest and nested ones, were used in this work. Compared with nested wave springs, crest-to-crest wave springs have lower damping and a larger range for the linear stiffness due to a reduced level of contact. Dynamic compressive tests, subject to different static compression levels, are carried out to investigate the force-displacement hysteresis of individual wave springs. The stiffness is shown to increase up to 800% when the static compression is at 40%. The crest-to-crest wave spring is shown to provide loss factors up to 0.12 while nested ones as high as 0.80. Testing also showed that performance did not degrade between room temperature and 100°C. The effect of different spring materials, inner diameter and flat spring width are also evaluated

Effect of section thickness on fatigue performance of laser sintered nylon 12

Laser Sintering offers manufacturers freedom of design, which enables creating parts with complex geometries. However, very little investigation has been made into the effects of geometry on mechanical properties of the parts. In the present study, Laser Sintered Nylon 12 parts with different section thickness are subjected to displacement controlled tension-tension and force-controlled fully reversed fatigue loading to investigate the effect of geometry on their fatigue behavior. Section thickness of the parts is shown to have no significant influence on the fatigue behavior under tension only loading. However, fatigue life of parts under fully reversed loading is shown to increase with section thickness

Motional phase maps for estimating the effectiveness of granular dampers

This paper evaluates simple but general links between the operating dynamic motional phases and the non-linear energy dissipation characteristics of granular dampers. The Discrete Element Method is used to simulate a typical granular medium consisting of spherical particles in a cylindrical enclosure subjected to harmonic vibrations aligned both parallel and perpendicular with gravity. A set of equivalent experiments is conducted to verify the numerical model. A wide range of excitation frequency and amplitude are considered, to obtain many different motional phases, along with particle size and volume fill ratio. Granular motional phase maps are produced over amplitude-frequency plane that defines where the various motion phases are present providing rich information for the effectiveness of granular dampers. Findings show that high granular damping effectiveness is found in two distinct zones: where collective collisions with the enclosure are optimised and where fluidisation without convection is maximised. The most significant factors affecting these high effectiveness zones are identified and can be used to provide guidance for those seeking to design granular dampers to reduce vibrations in structures

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

Mechanical behaviour of tangled metal wire devices

Tangled metal wire (TMW) devices can be used as damping elements in extreme environments where traditional materials such as viscoelastic polymers deteriorate or become ineffective. Dynamic properties of TMW devices are highly nonlinear because the microstructure consists of coiled metal wires that are compressed together. This paper examines the sensitivity of their dynamic stiffness and damping to loading conditions, in particular, pre-compression, dynamic amplitude and frequency of excitation. Using displacement-controlled experiments, it is shown that properties depend strongly on pre-compression and dynamic amplitude as would be expected in a structure comprising many frictional contact points. Frequency dependence is shown to be negligible over a broad frequency range that encompasses the region of interest for typical machine applications. This work identifies slow dynamic effects, with timescales of the order of around 10 s, which show that quasi-static testing, which is sometimes used for these materials, will not provide accurate estimates of dynamic properties