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Elastic Response (elastic + response)
Terms modified by Elastic Response Selected AbstractsA New Micromechanically Based Approach for the Elastic Response of Rubber,like Materials at Large StrainsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Serdar Göktepe M. Sc. The approach models the elasticity of a rubber,like materials based on micro,structure that can be symbolized by a micro,sphere. The proposed model incorporates both non,a.ne deformation of unconstrained chains and superimposed constraint e.ects of tube,like topological formations in a consistent manner. Framework of the constitutive modeling and numerical examples illustrating the excellent predictive capacity of the model are presented. [source] Seismic performance of a 3D full-scale high-ductility steel,concrete composite moment-resisting structure,Part I: Design and testing procedureEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2008A. Braconi Abstract A multi-level pseudo-dynamic (PSD) seismic test programme was performed on a full-scale three-bay two-storey steel,concrete composite moment-resisting frame built with partially encased composite columns and partial-strength connections. The system was designed to provide strength and ductility for earthquake resistance with energy dissipation located in ductile components of beam-to-column joints including flexural yielding of beam end-plates and shear yielding of the column web panel zone. In addition, the response of the frame depending on the column base yielding was analysed. Firstly, the design of the test structure is presented in the paper, with particular emphasis on the ductile detailing of beam-to-column joints. Details of the construction of the test structure and the test set-up are also given. The paper then provides a description of the non-linear static and dynamic analytical studies that were carried out to preliminary assess the seismic performance of the test structure and establish a comprehensive multi-level PSD seismic test programme. The resulting test protocol included the application of a spectrum-compatible earthquake ground motion scaled to four different peak ground acceleration levels to reproduce an elastic response as well as serviceability, ultimate, and collapse limit state conditions, respectively. Severe damage to the building was finally induced by a cyclic test with stepwise increasing displacement amplitudes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Carbon Nanotubes: High Electromechanical Response of Ionic Polymer Actuators with Controlled-Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Mater. Abstract Recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter-VA-CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA-CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA-CNTs to further enhanced performance. [source] High Electromechanical Response of Ionic Polymer Actuators with Controlled-Morphology Aligned Carbon Nanotube/Nafion Nanocomposite ElectrodesADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Sheng Liu Abstract Recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter-VA-CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA-CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA-CNTs to further enhanced performance. [source] The effect of particle shape and grain-scale properties of shale: A micromechanics approachINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2010J. A. Ortega Abstract Traditional approaches for modeling the anisotropic elasticity response of the highly heterogeneous clay fabric in shale have mainly resorted to geometric factors such as definitions of particles shapes and orientations. However, predictive models based on these approaches have been mostly validated using macroscopic elasticity data. The recent implementation of instrumented indentation aimed at probing nano-scale mechanical behaviors has provided a new context for characterizing and modeling the anisotropy of the porous clay in shale. Nanoindentation experimental data revealed the significant contribution of the intrinsic anisotropy of the solid clay to the measured elastic response. In this investigation, we evaluate both the effects of geometric factors and of the intrinsic anisotropic elasticity of the solid clay phase on the observed anisotropy of shale at multiple length scales through the development of a comprehensive theoretical micromechanics approach. It was found that among various combinations of these sources of anisotropy, the elastic response of the clay fabric represented as a granular ensemble of aligned effective clay particles with spherical morphology and anisotropic elasticity compares satisfactorily to nanoindentation and ultrasonic pulse velocity measurements at nano- and macroscopic length scales, respectively. Other combinations of sources of anisotropy could yield comparable predictions, particularly at macroscopic scales, at the expense of requiring additional experimental data to characterize the morphology and orientations of particles. Copyright © 2009 John Wiley & Sons, Ltd. [source] SANISAND: Simple anisotropic sand plasticity modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2008Mahdi Taiebat Abstract SANISAND is the name used for a family of simple anisotropic sand constitutive models developed over the past few years within the framework of critical state soil mechanics and bounding surface plasticity. The existing SANISAND models use a narrow open cone-type yield surface with apex at the origin obeying rotational hardening, which implies that only changes of the stress ratio can cause plastic deformations, while constant stress-ratio loading induces only elastic response. In order to circumvent this limitation, the present member of the SANISAND family introduces a modified eight-curve equation as the analytical description of a narrow but closed cone-type yield surface that obeys rotational and isotropic hardening. This modification enables the prediction of plastic strains during any type of constant stress-ratio loading, a feature lacking from the previous SANISAND models, without losing their well-established predictive capability for all other loading conditions including the cyclic. In the process the plausible assumption is made that the plastic strain rate decomposes in two parts, one due to the change of stress ratio and a second due to loading under constant stress ratio, with isotropic hardening depending on the volumetric component of the latter part only. The model formulation is presented firstly in the triaxial stress space and subsequently its multiaxial generalization is developed following systematically the steps of the triaxial one. A detailed calibration procedure for the model constants is presented, while successful simulation of both drained and undrained behavior of sands under constant and variable stress-ratio loadings at various densities and confining pressures is obtained by the model. Copyright © 2007 John Wiley & Sons, Ltd. [source] Tourism demand response by residents of Latin American countriesINTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 1 2009Manuel Vanegas Sr Abstract A general-to-specific methodology was used to build international tourism demand models by residents from Argentina, Brazil, Colombia and Venezuela to Aruba. We seek to evaluate demand parameters, especially elasticity values, which were disaggregated on a country-to-country basis. We also aim to learn more about the structure and important variables and investigate the process of adjustment. The study has provided new and compelling evidence that, in the short run, residents in developing countries respond rationally and substantially to economic stimulus. The short-run income elasticity ranges from the low of 1.52 for Venezuela to the high of 2.34 for Argentina. These results indicate that Aruba will benefit differently from income increases in these four Latin American countries. The coefficients of the price variable had the expected negative signs, inelastic in the short-run for all countries but significant at the 5% level for Venezuela only. Any deliberate effort to expand tourist arrivals will require a much larger decline in prices than would be the case in the presence of short-run elastic response. The adjustment elasticity, being less than one, suggests that a period of more than one year is required for Latin American residents to fully adjust their tourism decisions in response to demand shocks. This study would seem to provide some useful information about international tourism demand from developing to developing countries that could form a very good and solid basis for analyses and policy action. Copyright © 2008 John Wiley & Sons, Ltd. [source] Changes in Apple Liquid Phase Concentration throughout Equilibrium in Osmotic DehydrationJOURNAL OF FOOD SCIENCE, Issue 2 2007J.M. Barat ABSTRACT:, Previous results on apple tissue equilibration during osmotic dehydration showed that, at very long processing times, the solute concentrations of the fruit liquid phase and the osmotic solution were the same. In the present study, changes in apple liquid phase composition throughout equilibrium in osmotic dehydration were analyzed and modeled. Results showed that, by the time osmosed samples reached the maximum weight and volume loss, solute concentration of the fruit liquid phase was higher than that of the osmotic solution. The reported overconcentration could be explained in terms of the apple structure shrinkage that occurred during the osmotic dehydration with highly concentrated osmotic solutions due to the elastic response of the food structure to the loss of water and intake of solutes. The fruit liquid phase overconcentration rate was observed to depend on the concentration of the osmotic solution, the processing temperature, the sample size, and shape of the cellular tissue. [source] Error propagation in multiscale approaches to the elasticity of polycrystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008Martin Friák Abstract The error propagation properties of the Voigt, Reuss, Voigt,Reuss,Hill,Gilvarry, and Hershey schemes for the determination of the integral elastic response of texture free polycrystalline aggregates with cubic structure were studied. The sensitivity of the homogenized polycrystalline shear modulus was tested (i) analytically on the partial derivatives of the shear modulus with respect to the individual elastic constants within extremal Voigt and Reuss schemes, and (ii) numerically for all four methods. The sensitivity of the Hershey shear modulus on the input parameters, the single crystalline elastic constants B, C ,, C44, is shown to be within the limiting values found for the Voigt and Reuss schemes. This conclusion is illustrated numerically on a set of five cubic materials with very different physical properties. The influence of the bulk modulus was found to be approximately two orders of magnitude smaller than that of C , and C44. The Hershey modulus was also found to be non-linear, asymmetric, and strongly dependent on the level of the elastic anisotropy of the studied system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dynamic and capillary rheology of LDPE-EVA,based thermoplastic elastomer: Effect of silica nanofillerPOLYMER COMPOSITES, Issue 3 2010Shalmali Hui The effect of pristine silica nanoparticles on the dynamic and capillary rheology of a model LDPE-EVA thermoplastic elastomeric system is explored in this paper. The pristine silica nanoparticles were melt-blended with the LDPE-EVA system at 1.5, 3, and 5 wt% loadings, respectively, by varying the sequence of addition. In one of the compositions, coupling agent bis-[3-(triethoxysilyl)propyl] tetrasulphide (Si-69) was used to improve the interaction of hydrophilic silica particles with polymer matrix. Results obtained reveal that the viscoelastic behavior of such composites is influenced remarkably by loadings of silica, variation of sequence, and addition of Si-69. Upon addition of coupling agent, G, value increases especially at higher strain levels due to increased polymer-filler interactions. All systems with various loading of nanosilica represent an increase in elastic response with increasing frequency. Both the unfilled and filled blends exhibit rheological behavior of non-Newtonian fluids. But interestingly, the viscoelastic response varies markedly with the temperature. The dynamic and steady shear rheological properties register a good correlation in regard to the viscous vs. elastic response of such systems. Finally, the rheological behavior is correlated with morphology of the present system processed at various shear rates. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] Autonomous damage initiated healing in a thermo-responsive ionomerPOLYMER INTERNATIONAL, Issue 8 2010Russell John Varley Abstract The partially neutralised poly[ethylene- co -(methacrylic acid)] copolymer Surlyn 8940® (DuPont) ionomer exhibits damage-initiated healing during high-energy impact. This is attributed to the hierarchical structure of ionomers, arising from the presence of ionic aggregates and hydrogen bonding. This work investigates the mechanism of this process using novel techniques developed here. The ionomer's response to penetration has been found to consist of three consecutive events: an initial elastic response, an anelastic response and pseudo-brittle failure. In addition, the ultimate level of healing has been shown to be dependent upon the elastic response during impact as well as post-failure viscous flow. Increasing the local temperature at impact consistently increases elastic healing, although further improvements in healing are minor once the local temperature increases beyond the melting point. Below the order-to-disorder transition, microscopic investigations reveal severe plastic deformation while the lack of shape memory reduces the comparative level of elastic healing. Above this temperature, healing is facilitated by elastomeric behaviour at the impact site, while above the melting point a combination of elastomeric and viscous flow dominates. This work provides for the first time evidence of the consecutive healing events occurring during high-impact penetration for ionomers. The hierarchical structure of ionomers and its impact upon the microstructure have been shown to be critical to the process. Comparison of the mechanical response during impact with that of non-ionic polymers further highlights this. In addition, slow relaxational processes occurring post-impact are found to facilitate further recovery in mechanical properties. Copyright © 2010 Society of Chemical Industry [source] Do Small Farmers Borrow Less When the Lending Rate Increases?ASIAN ECONOMIC JOURNAL, Issue 4 2009Interest Rate Elasticity of Rice Farmers in the Philippines O160; O180; Q140 The new generation of credit programs directed at small borrowers emphasizes financial sustainability. Based on anecdotal information, proponents of cost recovery claim that raising formal lending rates would have a minimal impact on borrowing. However, rigorous evidence for this conjecture is sparse. The present study conducts an econometric test of this conjecture using data from a survey of small rice farmers from the Philippines. Alternative regression techniques tend to reject the conjecture; in particular, a regression that controls for selection effects shows a unitary elastic response of formal borrowing to the lending rate. [source] Cell Detachment Model for an Antibody-Based Microfluidic Cancer Screening SystemBIOTECHNOLOGY PROGRESS, Issue 5 2006Swapnil P. Wankhede We consider cells bound to the floor of a microfluidic channel and present a model of their flow-induced detachment. We approximate hydrodynamic force and cell elastic response using static finite-element simulation of a single cell. Detachment is assumed to occur when hydrodynamic and adhesive forces are roughly equal. The result is extended to multiple cells at the device level using a sigmoidal curve fit. The model is applied to a microfluidic cancer-screening device that discriminates between normal epithelial cells and cells infected with human papillomavirus (HPV), on the basis of increased expression of the transmembrane protein ,6 integrin in the latter. Here, the cells to be tested are bound to a microchannel floor coated with anti ,6 integrin antibodies. In an appropriate flow rate range, normal cells are washed away while HPV-infected cells remain bound. The model allows interpolation between data points to choose the optimal flow rate and provides insight into interaction of cell mechanical properties and the flow-induced detachment mechanism. Notably, the results suggest a significant influence of cell elastic response on detachment. [source] Stretchable, Curvilinear Electronics Based on Inorganic MaterialsADVANCED MATERIALS, Issue 19 2010Dae-Hyeong Kim Abstract All commercial forms of electronic/optoelectronic technologies use planar, rigid substrates. Device possibilities that exploit bio-inspired designs or require intimate integration with the human body demand curvilinear shapes and/or elastic responses to large strain deformations. This article reviews progress in research designed to accomplish these outcomes with established, high-performance inorganic electronic materials and modest modifications to conventional, planar processing techniques. We outline the most well developed strategies and illustrate their use in demonstrator devices that exploit unique combinations of shape, mechanical properties and electronic performance. We conclude with an outlook on the challenges and opportunities for this emerging area of materials science and engineering. [source] Surface Elastic Properties of Human Retinal Pigment Epithelium Melanosomes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Senli Guo Atomic force microscope (AFM) imaging and nanoindentation measurements in water were used to probe the mechanical properties of retinal pigment epithelium melanosomes isolated from 14-year-old and 76-year-old donors. Topographic imaging reveals surface roughness similar to previous measurements on dry melanosomes. Force-indentation measurements show different types of responses that were catalogued into four different categories. In these measurements no permanent surface damage of melanosomes was observed as revealed by imaging before and after indentation measurements. The indentation measurements that exhibited nearly elastic responses were used to determine the Young's modulus of melanosomes. The average Young's modulus values are similar for 14-year-old and 76-year-old melanosomes with a somewhat narrower distribution for the 14-year-old sample. These elastic modulus values are considerably higher than the modulus of organelles with cytoplasm (<1 MPa) and approaching values of the modulus of protein crystals (,100 MPa) indicating rather high packing density of biologic material in melanosomes. The width of the Young's modulus distributions is considerable spanning from few megapascals to few tens of megapascals indicating large heterogeneity in the structure. A fraction of the force curves cannot be described by the homogeneous elastic sample model; these force curves are consistent with ,10 nm structural heterogeneity in melanosomes. The approach-withdraw hysteresis indicates a significant viscoelasticity, particularly in the samples from the 14-year-old sample. Adhesion of the AFM probe was detected on ,3% and ,20% of the surface of 14-year-old and 76-year-old samples, respectively. In light of previous studies on these same melanosomes using photoelectron emission microscopy, this adhesion is attributed to the presence of lipofuscin on the surface of the melanosomes. This suggestion indicates that part of the difference in photochemical properties between the old and young melanosomes originates from surface lipofuscin. [source] | |||||||||||||||||||