Ratio Of Elasticity Research Articles

Processing Behaviour of High-cis Polybutadiene in Rubber Compounds

Compounding and extrusion are critical steps in the production of rubber compounds of a reliable quality within a given timeframe and hence at a reasonable cost. The materials used - including the rubber types -are varied in order to obtain improvements in product performance. One of the most important of the synthetic rubbers is neodymium polybutadiene (NdBR) which, because of its exceptional microstructure and macrostructure, offers outstanding properties. Through the use of high-cis NdBR, marked improvements have been obtained in end products in terms of dynamic performance and good fatigue and wear characteristics. At the same time, however, the processing behaviour of this type of rubber requires adjustments to be made at the compounding and extrusion stage. This can lead to problems in the handling of the milled sheet and profiles, resulting for example in severe surface roughness or die swell. In extreme cases the benefits of NdBR can be masked altogether if no adjustments are made to the processing stages. This paper presents countermeasures to improve the processability of NdBR by adapting the compounding and extrusion conditions to its specific requirements. The ratio of viscosity and elasticity is specific to each type of rubber and therefore requires individual adjustment of the processing conditions. We show that under appropriately adjusted conditions, even using NdBR grades with the highest molecular weights (e.g. Buna CB22), short compounding times and smooth milled sheets and extrusion profiles with a glossy surface can be obtained. Under these conditions neodymium polybutadiene rubbers provide a basis for an ideal combination of excellent material properties and improved processing behaviour. The positive characteristics of NdBR are retained when it is used in blended rubbers such as an SSBR/BR blend. The rules regarding the optimisation of process conditions for pure NdBR systems apply here too.

Efficiency factor and modulus of elasticity of lightweight concrete with expanded clay aggregate

Nowadays lightweight concrete is used on a large scale for structural purposes and to reduce the self-weight of structures. Specific grav- ity, compressive strength, strength/weight ratio and modulus of elasticity are important factors in the mechanical behavior of structures. This work studies these properties in lightweight aggregate concrete (LWAC) and normal-weight concrete (NWC), comparing them. Spe- cific gravity was evaluated in the fresh and hardened states. Four mixture proportions were adopted to evaluate compressive strength. For each proposed mixture proportion of the two concretes, cylindrical specimens were molded and tested at ages of 3, 7 and 28 days. The modulus of elasticity of the NWC and LWAC was analyzed by static, dynamic and empirical methods. The results show a larger strength/ weight ratio for LWAC, although this concrete presented lower compressive strength.

Cross-linked open-pore elastic hydrogels based on tropoelastin, elastin and high pressure CO 2

In this study the effect of high pressure CO 2 on the synthesis and characteristics of elastin-based hybrid hydrogels was investigated. Tropoelastin/α-elastin hybrid hydrogels were fabricated by chemically cross-linking tropoelastin/α-elastin solutions with glutaraldehyde at high pressure CO 2. Dense gas CO 2 had a significant impact on the characteristics of the fabricated hydrogels including porosity, swelling ratio, compressive properties, and modulus of elasticity. Compared to fabrication at atmospheric pressure high pressure CO 2 based construction eliminated the skin-like formation on the top surfaces of hydrogels and generated larger pores with an average pore size of 78 ± 17 μm. The swelling ratios of composite hydrogels fabricated at high pressure CO 2 were lower than the gels produced at atmospheric pressure as a result of a higher degree of cross-linking. Dense gas CO 2 substantially increased the mechanical properties of fabricated hydrogels. The compressive and tensile modulus of 50/50 weight ratio tropoelastin/α-elastin composite hydrogels were enhanced 2 and 2.5 fold, respectively, when the pressure was increased from 1 to 60 bar. In vitro studies show that the presence of large pores throughout the hydrogel matrix fabricated at high pressure CO 2 enabled the migration of human skin fibroblast cells 300 μm into the construct.

Cost recovery from congestion tolls with random capacity and demand

According to the Cost Recovery Theorem the revenues from congestion tolls pay for optimal capacity of a facility if user costs are homogeneous of degree zero in usage and capacity, and if capacity is perfectly divisible and supplied with a unit cost elasticity. This paper examines the robustness of the Theorem to demand and capacity uncertainty in the context of highway travel. Three main results are derived. (1) The Theorem holds in expected values when users are perfectly informed about the state and the toll is set optimally as a function of the state. (2) The Theorem also holds in expected values when users are imperfectly informed about the state, the toll is set optimally given the information that users have, and the price elasticity of demand is the same in all states. (3) The Theorem does not hold if the toll is set using less information than users have. Whether an expected surplus or deficit results depends on the sign of the correlation across states between the Pigouvian toll and the ratio of the price elasticity of demand to the price. Examples show that the correlation can be positive or negative depending on the functional form of the demand and cost curves and the way the curves shift between states.

Oral Intake of Soy Isoflavone Aglycone Improves the Aged Skin of Adult Women

A double-blind, placebo-controlled trial was conducted to clinically evaluate the effect of soy isoflavone aglycone on the aged skin of middle-aged women. Twenty-six women volunteers in their late 30s and early 40s were randomly assigned to receive either a test food (13 women, the test food group) or a placebo food (13 women, the control group). These groups were given the test food (40 mg of soy isoflavone aglycone per day) and placebo, respectively, for 12 wk. The extent of linear and fine wrinkles at the lateral angle of the eyes was selected as the major evaluation criterion to assess the effects of foods, and the wrinkles' area ratio was used as the evaluation parameter. The extent of skin microrelief at the lateral angle of eyes and that of malar skin elasticity were used as secondary evaluation criteria, and the skin microrelief's area ratio and recovery of skin elasticity were used as the respective evaluation parameters. These parameters were assessed 4, 8, and 12 wk after the start of the test food or placebo intake. The test food group showed a statistically significant improvement of fine wrinkles at week 12 (p<0.05) and of malar skin elasticity at week 8 (p<0.05), compared with the control group. Although there was no significant difference between the test food group and the control group regarding effects on skin microrelief at lateral angle of the eyes, a significant intragroup improvement was observed at week 8 in the test food group (p<0.05). As for the test food safety, none of the subjects presented adverse symptoms during the study period or discontinued the intake of the test food. These data indicate that the oral intake of 40 mg soy isoflavone aglycones per day improves the aged skin of middle-aged women.

Shear Strength of FRP-Reinforced Concrete Beams without Transverse Reinforcement

This paper studied the behavior and shear strength of concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Nine large-scale reinforced concrete beams without stirrups were constructed and tested to failure. The beams measured 3250 mm long, 250 mm wide, and 400 mm deep and were tested in 4-point bending. Test variables were the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. The test beams included 3 reinforced with glass FRP bars, 3 reinforced with carbon FRP bars, and 3 control beams reinforced with conventional steel bars. Test results were compared with predictions provided by the different available codes, manuals, and design guidelines, indicating that the relatively low modulus of elasticity of FRP bars results in reduced shear strength compared to that of control beams reinforced with steel. The current ACI 440.1R design method offered very conservative predictions, particularly for beams reinforced with glass FRP bars. Based on obtained experimental results, a proposed modification to the current ACI 440.1R design equation is given and verified against test results from other research.

Shear Capacity of High-Strength Concrete Beams Reinforced with Fiber-Reinforced Polymer Bars

This paper reports experimental data on the behavior and shear strength of high-strength concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Shear tests were conducted on six large-scale reinforced concrete beams without stirrups using high-strength concrete (f' c = 65 MPa) along with three beams using normal-strength concrete (f' c = 35 MPa). The beams measured 3250 mm long, 250 mm wide, and 400 mm deep, and were tested in four-point bending. The test variables were strength of concrete, and the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. Carbon and glass FRP bars and conventional steel bars were used as longitudinal reinforcement in this investigation. The experimental shear strengths of the FRP-reinforced concrete beams were compared to theoretical predictions provided by ACI 440.1R-03 and the modified form of this method proposed by the authors. The test results indicated that the high-strength concrete beams exhibited slightly lower relative shear strength compared to normal-strength concrete beams. In addition, the ACI 440.1R-03 design method provided very conservative predictions whereas the proposed modified equation gave better results.

Development of a tactile sensor for Braille pattern recognition: sensor design andsimulation

The purpose of this paper is to define the design criteria of a tactile sensor for Braille patternrecognition by investigating the influence of sensor geometry and material on sensoroutput. First, a single segment of a tactile sensor, consisting of a piezoelectric (PVDF) filmsandwiched between two elastic materials, is designed and simulated to read a single dot ofa Braille character. Applying different materials and thicknesses for layers surrounding thePVDF film, different simulations are carried out under two different boundary conditions.With regards to design concept and geometry of the sensor, the index of thickness(f), ratio of modulusof elasticity (e) andindex of sensitivity (a) are defined and discussed in detail by the simulation results. It is shown that these indicescould be the design criteria to estimate the performance of the sensor. Second, theconceptual design of a single segment is generalized to a whole sensor, and a completesensor, which can read two blocks of Braille characters, is designed and simulated. Theresults also show that the output of the sensor is more dependent on the bending effectnear the PVDF layer than on the compression on the PVDF. Finally, with regard to thesimulation results, the optimum design parameters for this Braille tactile sensor areconcluded.

Cross Linking and Rheological Characterization of Adsorbed Protein Layers at the Oil−Water Interface

The dilatational rheological properties of cross-linked protein layers adsorbed at the oil-water interface were investigated with help of a modified drop tensiometer allowing successive replacements of the external phase. This setup enables one to perform cross-linking reactions at the interface only, that is, without any contact between the cross-linking agent and protein molecules in solution, under continuous monitoring of the interfacial tension. The mechanical properties of the resulting interface were investigated with dilatational large strain experiments. Measured rheological properties were related to the expected stability of an emulsion against disproportionation by considering the ratio of the interfacial elasticity to the interfacial tension. In an attempt to increase this ratio to improve the resistance against disproportionation, experiments were performed with densified protein layers obtained via reduction of the droplet area prior to cross linking. To highlight the influence of the protein morphology on the dilatational rheological properties of the cross-linked adsorbed layers, experiments were performed with random coil (beta-casein) as well as globular (beta-lactoglobulin) proteins. Glutaraldehyde was used as a cross-linking agent. Experiments were performed at 55 degrees C and pH 7.0 in 20 mM imidazole buffer for later comparison with enzymatically cross-linked adsorbed protein layers. The present work demonstrated substantial qualitative and quantitative differences in the interfacial rheological properties of cross-linked random coil and globular proteins.

Modelling the effect of graphite morphology on the modulus of elasticity in cast irons

Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

A New Method of Estimating Risk Aversion

I show existing evidence on labor supply behavior places an upper bound on risk aversion in the expected utility model. I derive a formula for the coefficient of relative risk aversion (γ) in terms of the ratio of the income elasticity of labor supply to wage elasticity and degree of complementarity between consumption and labor. I bound the degree of complementarity using data on consumption choices when labor supply varies across states. Using labor supply elasticity estimates, I find a mean estimate of [Formula: see text], then show generating γ &gt; 2 requires that wage increases cause sharper labor supply reductions.

A Study on the Determination of Poisson’s Ratio and Modulus of Elasticity of Some Onion Varieties

A Study on the Determination of Poisson’s Ratio and Modulus of Elasticity of Some Onion Varieties

Willingness to Accept, Willingness to Pay and the Income Effect

The disparity between willingness to pay and willingness to accept in experimental and survey settings remains a troubling anomaly. Willingness-to-accept is almost always higher than WTP, often substantially higher. Our interest lies with the neoclassical explanation of Hanemann, who demonstrates that for exogenous quantity changes, the difference between WTP and WTA depends ratio of the ordinary income elasticity of demand for the good to the Allen-Uzawa elasticity of substitution between the good and a composite commodity. When the elasticity of substitution is low, this ratio will be large. The ratio WTA/WTP will then also be large. We use a result of Sugden to formulate the WTA/WTP ratio as a function of the income effect on WTP. We find that the WTA/WTP ratios provided by our comprehensive literature search imply income elasticities and income effects that are implausibly high; much higher than income effects found in the literature; and much higher than income elasticities estimated in the set of studies from which the WTA/WTP results are drawn. Based on the evidence, it is difficult to accept the idea that the observed ratios of WTA/WTP, garnered from a remarkably large and diverse set of studies, are consistent with a standard neoclassical model. Substitution among goods seems an inadequate explanation for the divergence between WTA and WTP.

Tracheobronchial mucus viscoelasticity during environmental challenge in horses with recurrent airway obstruction.

The goal of this study was to compare the rheological properties of mucus from horses with recurrent airway obstruction (RAO) to that from healthy controls during environmental challenge by stabling in stalls with straw as bedding and hay as feed. We determined viscoelasticity (log G* dyn/cm2, at 10 radian/s) and calculated mucociliary clearability index (MCI) and cough clearability index (CCI), which are derivative parameters of G* and the ratio of viscosity and elasticity measured at 1 and 100 radian/s, respectively. We also investigated the solids content of mucus, and cytology of bronchoalveolar lavage fluid (BALF). Samples were obtained before (0 h) and 6, 24 and 48 h after environmental challenge. The central findings were rheological changes in airway mucus, which occurred over time in RAO-affected animals, but not in controls. Mucus rheology was similar in both groups at 0 and 6 h. In RAO-affected horses, mucus viscoelasticity, as measured by log G*, increased from 2.49 +/- 0.18 dyn/cm2 (mean +/- s.e.) at 0 h to 3.05 +/- 0.13 dyn/cm2 at 24 h after environmental challenge, and was accompanied by significant decreases in MCI and CCI. Percent solids of mucus did not differ significantly between the 2 groups, nor over time. Rheological values did not correlate with BALF cytology. We conclude that viscoelastic properties of tracheal mucus samples from RAO horses in remission do not differ from those of normal horses. However, environmental challenge causes clinical signs of small airway disease and a concurrent increase in mucus viscoelasticity only in RAO horses. Therefore, we infer that unfavourable changes in mucus rheology may contribute to stasis and accumulation of mucus in RAO horses in exacerbation, but not in clinical remission.

Venous return in the fetal-placental cardiovascular system

For a quantitative understanding of the venous Doppler sonograms, a model of the fetal cardiovascular system is proposed which stresses the significance of flow. The model comprises three major components: the heart which provides constant power and dynamic capacitance, the peripheral fetal and placental vascular beds with flow limiting conductances (1/resistance), and the resistance of the hepato-ductal system. As long as cardiac power is maintained, the conductances control the flow rate and, depending upon hepato-ductal and ventricular filling resistance, the umbilical venous as well as the central venous pressure. According to the model, the mean flow velocity of venous return is total organ flow rate divided by cross sectional areas in the cardiac input system, i.e. the central veins, both atria and both AV valves respectively. The velocity pattern of venous return is related to cardiac performance and hepato-ductal resistance as follows: The E wave in early diastole describes the filling (driven by the central-venous pressure) of the relaxed ventricle. The time constant equals the ratio of elasticity over resistance in the ventricular wall. The A wave mirrors the contractility of atrial myocardium which is related to central venous pressure. The ratio of the forward A wave in the tricuspid valve to the backward A wave in the caval veins depends on ventricular capacitance. The S wave is related to systolic valvular shift. The velocity pulsations in the ductus venosus are transmitted backwards from the heart. The continuous velocity component in the ductus venosus and the non-pulsatile velocity in the umbilical vein are due to hepato-ductal and placental vascular resistance.

The role of the casimir effect in the static deflection and stiction of membrane strips in microelectromechanical systems (MEMS)

We present an analysis describing how the Casimir effect can deflect a thin microfabricated rectangular membrane strip and possibly collapse it into a flat, parallel, fixed surface nearby. In the presence of the attractive parallel-plate Casimir force between the fixed surface and the membrane strip, the otherwise flat strip deflects into a curved shape, for which the derivation of an exact expression of the Casimir force is nontrivial and has not been carried out to date. We propose and adopt a local value approach for ascertaining the strength of the Casimir force between a flat surface and a slightly curved rectangular surface, such as the strip considered here. Justifications for this approach are discussed with reference to publications by other authors. The strength of the Casimir force, strongly dependent on the separation between the surfaces, increases with the deflection of the membrane, and can bring about the collapse of the strip into the fixed surface (stiction). Widely used in microelectromechanical systems both for its relative ease of fabrication and usefulness, the strip is a structure often plagued by stiction during or after the microfabrication process—especially surface micromachining. Our analysis makes no assumptions about the final or the intermediate shapes of the deflecting strip. Thus, in contrast to the usual methods of treating this type of problem, it disposes of the need for an ansatz or a series expansion of the solution to the differential equations. All but the very last step in the derivation of the main result are analytical, revealing some of the underlying physics. A dimensionless constant, Kc, is extracted which relates the deflection at the center of the strip to physical and geometrical parameters of the system. These parameters can be controlled in microfabrication. They are the separation w0 between the fixed surface and the strip in the absence of deflection, the thickness h, length L, and Young’s modulus of elasticity (of the strip), and a measure of the dielectric permittivities of the strip, the fixed surface, and the filler fluid between them. It is shown that for some systems (Kc&amp;gt;0.245), with the Casimir force being the only operative external force on the strip, a collapsed strip is inevitable. Numerical estimates can be made to determine if a given strip will collapse into a nearby surface due to the Casimir force alone, thus revealing the absolute minimum requirements on the geometrical dimensions for a stable (stiction-free) system. For those systems which do exhibit a stiction-free stable equilibrium state, the deflection at the middle of the strip is always found to be smaller than 0.48w0. This analysis is expected to be most accurately descriptive for strips with large aspect ratio (L/h) and small modulus of elasticity which also happen to be those most susceptible to stiction. Guidelines and examples are given to help estimate which structures meet these criteria for some technologically important materials, including metal and polymer thin films.

Effect of long range order on sheared liquid crystalline materials Part 1: compatibility between tumbling behavior and fixed anchoring

A viscoelastic constitutive equation for liquid crystalline flows is presented in terms of tensor order parameter dynamics. The presented equation takes into account short range order, long range order (Frank elasticity), and flow effects, and captures the spatio-temporal evolution of the tensor order parameter. The dimensionless parameters arising in the theory are the Deborah (De) number and Ericksen (Er) number, and their ratio is a new dimensionless number R which represent the ratio of short range elasticity to long range elasticity. At Er → ∞ the model converges to the Doi equation, and for De → 0 to the Leslie-Ericksen director equation; the consistency with the Doi theory is shown by the classical shear flow solutions: tumbling, oscillating, and steady state. The model is used to analyze rectilinear simple shear flow subjected to strong anchoring conditions. For the range of governing parameters studied in this paper it is found that for small Er, a spatially nonhomogenous steady state of the tensor order parameters exists. For De corresponding to the tumbling solutions of the Doi equation, the present theory predicts the presence of a composite three layer structure: (a) a center bulk region characterized by director tumbling; and (b) two director oscillating regions next to the bounding surfaces. The amplitude of the director oscillations decrease from a maximum at the boundaries between tumbling-oscillating modes to zero at the bounding surfaces. The boundary between the tumbling-oscillating mode is characterized by the time periodic emergence of an abnormal nematic state, which is characterized by a tensor order parameter with two equal eigenvalues on the shear plane. The emergence of the abnormal nematic state provides for a compatibility mechanism between oscillations and rotations. Thus, we have found through the use of computational modeling a new mechanism that explains the compatibility of Doi's tumbling solutions and fixed surface anchoring conditions. The new flow mechanism is independent of the type of strong anchoring conditions, and arises with planar, homeotropic, and any arbitrary director anchoring.

Identification of Anisotropic Parameters for Hybrid Laminated Composites Using FEM Eigenvalue Analysis.

Elastic parameters are essentia for structural analysis. The elastic parameters of laminated composite materials, however, are difficult to determine by either theoretical or experimental approaches because of their anisotropy. This paper presents an inverse anaysis method to identify anisotropic parameters of laminated composite materials using FEM eigenvalue analysis. A shell element model is formulated for unsymmetrically laminated composites. The modal assurance criterion, MAC, is adopted to compare analyzed vibration modes with observed modes, because the order of vibration modes of anisotropic materials changes according to the ratio of elasticity EL/ET. As numerical examples, elastic Parameters of single-and multilayered composite plates are identified.

Effect of Sorption Hysteresis on Mechanical Behavior of Canola

Creep-recovery tests were conducted on single canola kernels. The samples were conditioned by bringing them to equilibrium through the adsorption or desorption process to the same final moisture. Prior to the creep-recovery tests, kernels were subjected to cyclic loading to minimize the influence of plasticity. The comparison of the elasticity ratio and modulus of elasticity was made between the adsorption and desorption groups. The ratio of elasticity was from 18 to 38% higher for kernels brought to equilibrium through adsorption than through desorption.

Random vibration of beams with localized region of damage

The random response of beams with localized zones of damage under stochastic excitation is studied using finite element analysis. The ratio of the stiffness elasticity of the damaged region to that of the undamaged beam is considered as a measure of the damage extent. The problem is formulated in the frequency domain by Fourier transformation of the dynamic equilibrium equation for a structurally damped system. The stiffness and mass matrices of the discretized structural system are condensed to reduce the basic degrees of freedom to transverse deflections only. The developed model is based on the method of complex matrix inversion to calculate the power spectral densities of response characteristics within a cut-off frequency range. The model is illustrated by two examples, namely, a simply supported beam and a five-span continuous beam subjected to damage under clipped white noise and acoustic jet noise excitation, respectively. Numerical results are presented along with those of an undamaged beam obtained by the present method. Flexural free vibration analysis of beams subjected to damage is also carried out to study the shifts in the eigenparameters.