Papers by Keyword: Viscoelastic Material

Abstract: The change about molecular chain of viscoelastic material in salt fog environment was tested by FTIR. The effects of salt fog aging on material and damping capacity of the damping layer in the constrained damping structure were researched by macro-mechanical properties and micro-molecular chain movement. The results showed that salt fog could reduce the mechanical properties of the viscoelastic material, the chemical bonds of molecular which were mainly hydrogen bonds had varying degrees of breaking, the composite loss factor of constrained damping structure decreased over time, and the vibration acceleration level increased gradually. The composite loss factors of the viscoelastic material after 90 days salt fog aging were 0.2047 and respectively, which illustrated that the material still had strong energy dissipation capacity.

Abstract: In order to effectively evaluate the acoustic vibration characteristics of viscoelastic sandwich composite cylindrical shell, based on FEM and BEM method, the vibration acoustic radiation of the viscoelastic sandwich panel and metal shell are calculated, and the results agree well with the experimental results. The dynamic mechanical parameters of viscoelastic core are obtained by dynamic thermodynamic experiments and the equivalent principle of temperature and frequency. The finite element method is used to simulate the coupling of water and shell. Finally, the indirect boundary method is used to calculate the radiated sound field under point excitation and the results show that the average and peak value of the acoustic power of the viscoelastic sandwich composite shell is 21.2dB and 46.4dB lower than that of the steel shell. In the range of low frequency,the radiation sound power is sensitive to the change of the layer angle,which is opposite in the range of high frequency. In the range of high frequency,the shear loss of the viscoelastic core is relatively obvious,which is opposite in the range of low frequency.

Abstract: With the ever-growing demand for further increase in the integration density of semiconductor devices, silicon wafers as the substrates for most devices are required to be extremely flat. In particular, it is strongly required to suppress edge roll-off, which seriously deteriorates the surface flatness near the wafer edge during polishing process in the final stage of the wafer manufacturing. In this study, we investigate the properties of polishing pads required for decreasing edge roll-off and propose the evaluation method of the properties. Polishing experiments with silicon wafers and evaluation tests for polishing pads reveal that the proposed method can estimate the obtained edge surface flatness.

Abstract: Microgrooves with a pitch at wave length level are increasingly needed in the optical system. Conventional, the microgroove forming accuracy is low due to the incomplete filling of the material in the cavity of microgroove mold, and surface flaws occur easily due to the adhesion of the resin material to the mold surface. In this research, the response behavior of resin material subjected to alternating stress is resolved based on Generalized Maxwell model. Finite Element Method (FEM) simulation is carried out to test the microgroove forming effects under the pressing condition without and with ultrasonic vibration. An ultrasonic assisted pressing machine is developed and used to fabricate microgrooves on methacrylic resin surface. Form accuracy and surface quality of microgrooves are confirmed to be improved by comparing the ultrasonic assisted pressing with the conventional forming.

Abstract: The influence of foaming agent on the properties of steel-reinforced beams made of recycled plastic material is studied in the paper. The foaming agent creates a porous core in the recycled plastic elements. This core must be reflected when deriving the beam effective properties to be used in macroscopic simulations. To that end, standard image analysis combined with nanoindentation and the Mori-Tanaka micromechanical model is adopted to identify elastic material properties of the plastic material both inside and outside of the core. These are expected to enter an independent macroscopic analysis of the steel-reinforced beams.

Abstract: The ecological structures of some organisms that could resist environmental vibration naturally (such as dragonfly, woodpecker and legs of cursorial animals) uncovered by biologists inspire people a new approach to overcome the above problem. In this paper, a new shock isolation system consisting of a pedestal, a rubber layer, an air spring and a shearing viscoelastic damper is designed, fabricated, and characterized to avoid the performance deterioration and physical damage of mechanical manufacturing devices from external mechanical excitations. The nonlinear dynamics model of the platform is developed and the dynamic characteristics are analyzed using numerical analysis. The displacement and velocity response are obtained. The results demonstrate that the stiffness and damping characteristic of the platform change with excitation frequency. The vibration isolation effectiveness will be greatly enhanced.

Abstract: This paper presents the analysis of the contact surfaces between a rigid cylinder and a soft plate for viscoelastic material. The contact pressure and deformation of the plate in contact region were determined using finite element technique. Moreover, the characteristics of two surfaces of cylindrical roller and plate under elastohydrodynamic lubrication with nonNewtonian fluid were examined using finite difference technique with full adaptive multigrid method . In this study the simulation of viscoelastic material in contact was under taken to determine the effects of material behaviors on the deformation of plate compared to the elastic materials. The results indicated that the deformation shapes were nonlinearly dependent with the applied loads. Furthermore, the deformation of elastic material would reach a certain value in a period of time whereas the deformation of viscoelastic material was increased inconsistently with time. The film pressure and film thickness profiles in the contact regime were investigated at various loads. The minimum film thickness occurs near the trailing edge of contact region and becomes very small under heavy loads.

Abstract: In this paper, dynamic instability behavior of a linear viscoelastic panel in supersonic flow is investigated. The quasi-steady piston theory of supersonic flow is employed for the aerodynamic pressure. The partial differential governing equation of isotropic flat panel is derived by introducing viscoelastic structural damping based on Kelvins model. The panel governing equation is transformed into a set of ordinary differential equations via the Galerkin approach. First-order state equations are afterwards obtained and solved by means of a standard eigenvalue calculation. The dynamic instability of viscoelstic panels is predicted by the feature of characteristic roots. The phenomena of coupled-mode flutter without structural damping and single-mode flutter with structural damping induced by the supersonic flow are observed for the different dynamic pressure values. Results indicate that structural damping plays an important role for the stability of panels flutter. Flutter threshold keeps decreasing as viscoelastic structural damping is increased.

Abstract: A measurement method for loss factor of viscoelastic material was researched. When acoustic wave incident to the surface of submerged elastic plate coated with viscoelastic damping layers, according to boundary conditions of interfaces relationship between reflection acoustic wave in water and loss factor of viscoelastic material was derived. The change of loss factor as frequency goes was also simulated. Loss factor is related to frequency and other parameters of viscoelastic material.

Abstract: Applied damping material (ADM) is today widely used to reduce vibrations and sound radiations by damping out the resonant peaks of structures. The efficient use of ADM becomes more and more important from an optimization design view. In this paper, the potential of using topology optimization as a design tool to optimize the distribution of ADM on a vibrating plate to minimize its sound radiation is investigated. A solid isotropic material with penalization model is described based on a special interface finite element modeling for viscoelastic layer. Numerical analysis has been applied to demonstrate the validation of the proposed approach and shows that significant reductions of the sound radiation powers over a broadband frequency range are achieved by the optimized results.