Estimation of damping capacity of rubber vibration isolators under harmonic excitation (original) (raw)
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19th International Scientific Conference Engineering for Rural Development Proceedings
Rubber and rubber-like materials (elastomers) are widely used for anti-vibration mounts and shock absorbers for vehicles, machinery, building structures due to their specific properties: ability to absorb vibration and shock loads, low elastic modulus, high mechanical strength, high elongation at brake, reversible elastic deformation. Rubber is a material that is capable of recovering from large deformations quickly and forcibly, which is suitable for work under cyclic loading. During deformation elastomeric materials absorb in an irreversible way part of the energy, causing this deformation. The energy absorbed during each cycle heats the deformed rubber element and dissipates in media. Heat generation in rubber causes additional stresses and deformations which are poorly known, and they are a subject of our study. In the presented paper the work of a rubber anti-vibration mount in the form of a straight circular cylinder under action of cyclic loading is studied. Poisson's ratio of the rubber material is μ = 0.5, the weight of the mount is not taken into account. Temperature field is assumed known based on the previous work (it depends on the frequency and amplitude of vibration, heat conductivity and heat capacity of the material, etc.). The stress-strain state analysis was carried out based on the Reissner variational principle. Analytical dependences for temperature additions to stresses and displacements are derived that allows estimating stiffness of the anti-vibration mount and its increase as a result of self-heating. Obtained results may be useful for proper design of anti-vibration mounts allowing changing geometrical dimensions in order to reach the required temperature field.
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The vibration dampers, shock absorbers, seismic isolation, bearing seals, compensation devices are widely applied in civil engineering, machine manufacturing and shipbuilding, aviation and aerospace engineering. For these details fabrication elastomeric materials are used. Rubber and rubber-like materials (elastomers) have the capability of absorbing input energy much better than other engineering materials. Elastomeric materials give many engineering advantages due to their high elasticity, good dynamic properties, low volume compressibility, a linear relationship between stress and strain at small and middle deformation, resistance to aggressive environmental factors. The disadvantage of elastomeric materials is ageing, i.e. changing their mechanical properties over time and lowering their operational capability. In given paper the influence of ageing of elastomeric materials on the damping properties of shock absorbers is considered based on the mechanical models of elastomers-Maxwell and Burgers modes.
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2004
Rubber vibration isolators are used for vibration isolation of engines at high frequencies. To make a good prediction regarding the characteristics of a vibration isolator in the design process, numerical models can be used. However, for a reliable prediction of the dynamic behavior of the isolator, the rubber material parameters have to be known. In practice the material parameters have to be determined with help of experiments. Normally a Dynamic Mechanical Analyzer (DMA) is used to measure the dynamic material properties of test samples of the rubber. However, test samples of the rubber part of the mount are often not available. For this reason a procedure is developed to determine the parameters that describe the material behavior of an isolator with the help of measurements of the entire isolator. Two measurements are used: a static force-displacement and a dynamic transfer stiffness measurement. A finite element model (ABAQUS) of the mount is made and the material parameters a...
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This work presents the results of a study carried out to characterize the mechanical response of a high damping rubber to be used in designing and constructing energy dissipating devices and base isolators for controling strong vibrations in civil engineering structures. A new parametric model of the elastomer is proposed to be employed in the design procedure and structural analysis of passive controlled structures. The parameters of the model are calibrated using experimental data obtained from tests on rubber specimens under different loading paths. The main dissipating energy mechanisms of the rubber are identified. The proposed model is able to reproduce those main mechanisms as well as geometric second order effects such as tension stiffening due to the effect of axial strains in the response. The response predicted by the proposed model is compared with that obtained from experimental tests and from the Kelvin and plasticity models.
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This paper presents experiments and numerical simulations of a nonlinear rubber isolator subjected to both harmonic and broadband random excitations. Harmonic and broadband random excitations are performed experimentally in order to show the softening effect of the rubber isolator for high amplitudes of displacement and to show the temperature dependency of its mechanical properties. Firstly, the rubber isolator is modeled as a one degree-of-freedom system, whose stiffness and damping depend only on the amplitude of the relative displacement of the joint. The relationship between the stiffness and the damping versus the amplitude of the relative displacement of the rubber isolator is updated via experiments. Secondly, the Harmonic Balance Method (HBM) and the shooting method are presented and extended to take into account both harmonic and random excitations. A modification of the nonlinear methods is necessary in order to recover the information concerning the displacement amplitude. Moreover, for random excitations, a periodogram strategy is used to ensure a good estimate of the resulting Power Spectral Density (PSD). Finally, comparisons between experiments and simulations are undertaken. Good correlations are observed for harmonic and broadband random excitations, thus validating the modeling of the rubber isolator and the proposed nonlinear methodology.
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The pneumatic tyre is excited by the road unevenness at a frequency close to its first radial mode for the speeds of 50-60 km•h-1. The first resonance of the belt of a radial-type pneumatic tyre has a frequency about 100 Hz. These oscillations are associated with amplitudes of displacement less than 1 mm. The vibrations at the resonance frequency go through the suspension elements and reach the vehicle body without noticeably reducing their amplitude. These high frequency vibrations have a major role in the vibro-acoustic comfort in the passenger compartment of a vehicle. The telescopic shock absorber is one of the suspension components. In the frequency range up to 20 Hz, it has a fundamental role in damping the oscillations generated by the road unevenness. In the frequency range of the natural modes of both sprung and unsprung masses (0.9-12 Hz), the displacements between both ends of a shock absorber are over 5 mm. High-frequency vibrations with an amplitude less than 1 mm do not activate the shock absorber damping properties. The amplitudes are not big enough to create the necessary pressure drop between the two chambers above and under the piston and to provide viscous damping. Other elements that have an influence on damping vibrations with frequencies above 50 Hz are the rubber mounts of the shock absorber. The work explores the behaviour of a telescopic shock absorber and its rubber mounts in the frequency domain determined by the resonances of the pneumatic tyre belt. A method for obtaining the damping coefficient of the rubber mounts for the shock absorberis presented. The purpose of the work is to determine the influence of the damping properties of the shock absorber and its rubber mounts on the vibrational behaviour of the suspension in the frequency range 50-150 Hz. The results of the work can be used to select a proper shock absorber and its rubber mounts, in order to improve the vibro-acoustic comfort of the passenger compartment.
In this work the results of a study carried out to characterize the mechanical response of a high damping rubber to be used to design and construct energy dissipating devices and base isolators for controlling strong vibrations in civil engineering structures is presented. A new parametric model of the rubber is proposed to be employed in the design procedure and structural analysis of passive controlled structures. The parameters of the model are calibrated using experimental results obtained from tests on rubber specimens subjected to different loading paths. The response predicted by the proposed model is compared with these obtained from experimental tests.