Papers by Keyword: Viscoelasticity

Abstract: The work reported in this paper describes the behavior and prediction of damping properties of the 3D composite laminated engine mount shell structure. The shell structure has a shape of box with four vertical and two horizontal plates with the thickness of 15mm and 20mm respectively. For more accurate prediction of the structural behavior, many researchers have incorporated the time dependent property of the material into their field of studies. In this article the finite element approach utilizes the concept of viscoelastic damping, which is carried out by direct integration. This paper describes the potential application of composite material as a damper device because of its damping, high stiffness and low weight properties, which favor the use as engine mount in submarine and ships where weight is the highest priority.

Abstract: The purpose of this work was to investigate the effects of pre-load static load and dynamic load on the visco-elastic in polycarbonate. In the paper, static-dynamic sweep experiment of polycarbonate was performed on EPLEXOR 500N, which was manufactured by GABO of Germany. The variation laws of storage modulus, loss modulus and loss tangent as changing dynamic load in a large range were systematically analyzed and the spectral characteristics of dynamic-viscoelastic under static-dynamic loads were obtained. The experiment results on dynamic visco-elastic under the high load shows that the load effects on dynamic visco-elasticity of polycarbonate performing on the changing of the dynamic visco-elastic parameters, storage modulus become lager with the increasing of static load and decreasing with the increasing of dynamic load, while loss tangent decreases with the increasing of dynamic load and varies in a more complicated pattern as the increasing of static load.

Abstract: Although blade coating materials dissipate vibratory energy while acting as thermal barrier coatings or protecting the substrate against corrosion or erosion, the inherent nonlinearity of these materials complicates the determination of the necessary material parameters. While plasma-sprayed ceramics alone do not appear to provide the desired levels of dissipation, notable increases in damping have been found to result from the inclusion of small amounts of viscoelastic materials. With proper selection of the added component, the resulting coating may be tailored for high damping in a specific temperature range. Vacuum infiltration of polymeric components into plasma-sprayed ceramics raise the dissipation to desired levels for temperatures of 93-135 oC; co-spraying mixtures of ceramics and glass frits leads to extremely high damping in the transition range of the glass, typically 550-800 oC.

Abstract: The present paper surveys briefly the parameter identification methods widely used in case of generalized Maxwell-model. Beside those basing on dynamical-mechanical thermal analysis (DMTA) and stress relaxation measurement authors have presented a technique using simple tensile tests. The latter can be effectively used by combining it with the genetic algorithm of Matlab for parameter identification in a limited frequency/time domain. The proposed method can be generalized easily for example for shear and compression tests too. After comparing it with other existing methods author make a proposal for the strain rate of the uniaxial tensile test.

Abstract: In recent years, the achievement of further high flatness of workpiece edge shape is strongly required in mirror finishing. Especially, the edge roll off of silicon wafers as the substrates of semiconductor devices is demanded to decrease in the polishing process for raising the yield of IC chips. Many theoretical and experimental analyses for the edge roll off generation have been already done to meet the demand. The analyses, however, cannot fully account for the obtained edge shape in actual polishing. Concretely, the influence of the polishing pressure as one of the key polishing conditions on the edge roll off has not been clarified. In this study, the influence of the polishing pressure on the edge shape was investigated by the polishing experiments and the edge roll off generation analyses using the model based on the viscoelasticity of the polishing pad, which was proposed in the previous study. And it was revealed that an appropriate polishing pressure is needed to be set for achieving high flatness of workpiece edge shape with the consideration of the properties of applied polishing pads.

Abstract: Nanoparticles have been used with polymer to make composites having remarkable properties. An attempt was made in this direction, in order to enhance the mechanical and tribological properties of nanocomposites. In the paper, the polytetrafluroethylene (PTFE) polymer-based nanocomposites filled with serpentine (SPT) and reinforced with different nanoparticles such as nano-β-carborundum whisker (β-SiCw), nano-copper and nano-TiO2 were prepared by using cold briquetting and hot-press sintering technologies. Also, the mechanical performances of these nanocomposites were studied. The quasi-static tensile experiments and dynamic mechanical thermal analysis (DTMA) were carried out. The results obtained showed that the mechanical properties of these nanocomposites stronger depend on the variety of nanoparticle. Stress-displacement and stress relaxation curves indicate that theses composites are typical viscoelastic materials. These research findings are believed to be helpful for providing practical guide in applications.

Abstract: A viscoelastic model is developed to describe the mechanical response of fiber-reinforced elastomeric composites at large deformation. A continuum approach is used to model the macroscopic mechanical behavior of elastomeric materials reinforced with unidirectional fibers, in which the resin and fibers are regarded as a single homogenized anisotropic material. The anisotropic viscoelastic constitutive model is developed considering transient reversible network theory. An efficient computational algorithm based on micromechanical modeling is proposed to relate the material parameters of constitutive model to the mechanical properties of composite constituents at finite strain. The microstructure is identified by a representative volume element (RVE) and it is subjected to large deformation with considering the conformity of opposite boundaries. The material parameters of the viscoelastic constitutive law are determined based on the response of heterogeneous microstructure which is examined under different loading conditions.

Abstract: Dye-coupled polyhedral oligomeric silsesquioxane (POSS) were prepared and the coloured POSS particles were ultrasonically solution dispersed in poly(styrene-b-butadiene-b-styrene) (SBS). POSS molecules contained either isobutyl or phenyl groups to provide selective compatibility with either the soft (butadiene) or hard (styrene) phase within the block copolymer. The composition and thermal stability were characterised using thermogravimetry. Colour coordinates were measured. Tensile mechanical properties, creep and recovery were determined. Creep was modeled using the 4-element model of Maxwell and Kelvin-Voigt, while recovery correlated with the stretched-exponential function of Kohlrausch, Williams and Watts.

Abstract: Based on the nonlinear finite element analysis method, FEA models which describe the viscoelastic friction contact state of the polyurethane foam preloaded structures are created. In the simulations, the general Maxwell viscoelastic constitutive relation is introduced and a seven-parameter general Maxwell viscoelastic model is used to fit the experimental stress relaxation curve of polyurethane foam. During the nonlinear contact analysis, coulomb friction law is adopted, and the effects of the coulomb friction coefficient on the reaction force in the axial direction are analyzed. The FE results show that the change tendencies of relation curves of the structures are similar to which of the polyurethane foams. In the end, the influences of stiffness ratio of polyurethane foam to the outer component on the structural relaxed force are discussed, and the FE results indicate that the stiffness ratios affect the stress (force) relaxation degree remarkably. That is to say a good structure design could optimize the mechanical performance of the complicated structures greatly.

Abstract: The viscoelastic flow and swell behaviors of polymer melts in the profile extrusion process can significantly influence the performance and dimension of the final products. In the study, the viscoelastic flow pattern of a commercial low density polyethylene (LDPE) extruded through out of the hollow profiled extrusion die is investigated by means of finite element simulation. The mathematical model of three-dimensional viscoelastic flow and swell of polymer melts is established with a differential Phan-Thien and Tanner (PTT) constitutive model. A penalty method is employed to solve the non-linear problem with a decoupled algorithm. The computation stability is improved by using the discrete elastic-viscous split stress (DEVSS) algorithm with the inconsistent streamline-upwind (SU) scheme. A streamface-streamline method is introduced to adjust the swelling free surface of the extrudate. The essential viscoelastic flow characteristics of LDPE flowing through out of the hollow profile extrusion die is investigated based on the proposed numerical scheme. Both the redistribution of flow velocity and the release of stress are found to be the reasons for the swell phenomenon.