Elasticity characteristics

The rolling resistance coefficient of a tire depends on the construction of the tire carcass, the elastic characteristics of the tire material, the tread design, and characteristics of the roadbed. It increases with decreasing wheel diameter, tire underinflation, and roadbed compliance. It decreases as the operating temperature of the tire rises. 

Viscoelasticity illustrates materials that exhibit both viscous and elastic characteristics. Viscous materials tike honey resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just as quickly return to their original state once the stress is removed. Viscoelastic materials have elements of both of these properties and, as such, exhibit time-dependent strain. Viscoelasticity is the result of the diffusion of atoms or molecules inside an amorphous material. Rubber is highly elastic, but yet a viscous material. This property can be defined by the term viscoelasticity. Viscoelasticity is a combination of two separate mechanisms occurring at the same time in mbber. A spring represents the elastic portion, and a dashpot represents the viscous component (Figure 28.7). 

Ctjki is a fourth order tensor that linearly relates a and e. It is sometimes called the elastic rigidity tensor and contains 81 elements that completely describe the elastic characteristics of the medium. Because of the symmetry of a and e, only 36 elements of Cyu are independent in general cases. Moreover only 2 independent rigidity constants are present in Cyti for linear homogeneous isotropic purely elastic medium Lame coefficient A and /r have a stress dimension, A is related to longitudinal strain and n to shear strain. For the purpose of clarity, a condensed notation is often used... 

New polymer structures allow the control of processability and final characteristics. For example, Mitsui is launching nanostructured metallocene alpha-olefins that have a crystallite size of the order of nanometres instead of microns as for conventional metallocene polyolefins. This yields a better balance of transparency, heat resistance, flexibility and elasticity characteristics. Targeted applications are automotive interior trim, packaging film, construction materials, protective films for electronic and optical parts, sealing products and as polymer modifiers. 

Materials are modeled classically as either viscous, such as water or molasses, or elastic in nature, such as steel beams or metal springs. In general, polymers are complex materials that behave in a combined response to strain with both viscous and elastic characteristics. Under conditions where the material exhibits both viscous and elastic rheological behavior, the polymers are described as viscoelastic. That is, polymers have substantial viscous and elastic characteristics when strained. 

The systematic investigation of the influence of the topological structure of weakly charged networks on the type of occurrence of the transition in the collapsed state was performed by Ilavsky and coworkers [42, 43]. In these papers, the authors studied the swelling and the elastic characteristics of PAA gels, containing a small number of anionic SMA groups. It has been shown that ... 

Differences between materials were detected in all of the employed methods (1—13) while in the comprehensive work cited above it has been noted that elastic characteristics of materials are more sensitive to minor changes in the molecular structure than the viscous ones. 

Products are comminuted with cutting tools such as shears, knives, or razor blades. Drilling, milling, etc. are also suitable. A smaller particle diameter can also be obtained by grinding precooled samples in mills. Depending on the elasticity characteristics of the sample, either dry ice or liquid nitrogen can be effectively used. 

With the above information, it becomes possible to combine viscous characteristics with elastic characteristics to describe the viscoelasticity of polymeric materials.86-90 The two simplest ways of combining these features are shown in Figure 2.49, where a spring having a modulus G models the elastic response. The viscous response is modelled by what is called a dashpot. It consists of a piston moving in a cylinder containing a viscous fluid of viscosity r. If a downward force is applied to the cylinder, more fluid flows into it, whereas an upward force causes some of the fluid to flow out. The flow is retarded because of the high viscosity and this element thus models the retarded movement and flow of polymer chains. 

The most straightforward rheological behaviour is exhibited on the one hand by Newtonian viscous fluids and on the other by Hookean elastic solids. However, most materials, particularly those of a colloidal nature, exhibit mechanical behaviour which is intermediate between these two extremes, with both viscous and elastic characteristics in evidence. Such materials are termed viscoelastic. 

Viscoelastic materials are those which exhibit both viscous and elastic characterists. Viscoelasticity is also known as anelasticity, which is present in systems when undergoing deformation. Viscous materials, like honey, polymer melt etc, resist shear flow (shear flow is in a solid body, the gradient of a shear stress force through the body) and strain, i.e. the deformation of materials caused by stress, is linearly with time when a stress is applied [1-4]. Shear stress is a stress state where the stress is parallel or tangencial to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. The variable used to denote shear stress is r which is defined as ... 

Elastomers. Elastomers are polymeric materials with irregular structure and weak intermolecular attractive forces. Elastomers are capable of high extension (up to 1000%) under ambient conditions. That is, they have the particular kind of elasticity characteristic of rubber. The elasticity is attributed to the presence of chemical and/or physical crosslinks in these materials. In their normal state, elastomers are amorphous, and as the material is stretched, the random chains are forced to occupy more ordered positions. Releasing the applied force allows the elongated chains to return to a more random state. Thus, the restoring force after elongation is largely because of entropy. (Fig. 14.3)... 

Disperse phase volume fraction. The viscosity of food emulsions tends to increase with increased disperse phase volume fraction (Figure 10). The viscosity increases relatively slowly, with 4> at low droplet concentrations, but increases steeply when the droplets become closely packed together. At higher droplet concentrations, the particle network formed has predominantly elastic characteristics. 

Two-part polysulphide sealants in the cured state have elastoplastic and elastic characteristics. A movement accommodation factor of 25%-30% is possessed by low-modulus sealants and one of 10%-20% by high-modulus sealants. The life expectancy is 20-25 years. They are more suitable for sealing larger joints and also joints that are subject to a somewhat larger degree of movement than are one-component sealants. 

Numerical studies [167] of planar (d = 2) elastic random percolation networks have shown that if their linear dimension L < 0.2c (c is the correlation length), then Poisson s ratio for the system is negative, and if L > 0.2J , Poisson s ratio is positive In this case, if L/c —> oo, the limiting value of Poisson s ratio is vp = 0.08 0.04 and is a universal constant that is, it does not depend on the relative values of the local elastic characteristics If... 

Viscoelasticity is the property of materials that exhibit both viscons and elastic characteristics when nndergoing deformation. To nnderstand flnid viscoelasticity, we need to start with the flnid viscous and solid elastic behaviors that are well known. 

The dependence of mechanical behavior on constitution in Zr02-Ni system results from the variation of microstructure and its distribution. In the regions rich in Ni or PSZ, the mechanical performance is controlled by continuous matrix component and displays elasto-plastic or linear elastic characteristics, respectively. The non-linear elastic behavior at 60 vol% PSZ is related to the connectivity transition of matrix component. 

Drawing is a process similar to dry-spinning, in which nanofibres are drawn slowly from the droplet of a polymer solution by a micropipetter. The polymer solution is made from a viscoelastic material (i.e., one exhibiting both viscous and elastic characteristics upon deformation) that can accommodate the extensive deformation caused by drawing and retain the integrated form of an ultrafine fibre (Ondarcuhu and Joachim, 1998). 

Rothe, C. F. and Gaddis, M. L. 1990. Autoregulation of cardiac output by passive elastic characteristics of the vascular capacitance system. Circulation 81 360. 

Ethylene-propylene rubbers are the important class of elastomers and are widely used in many branches of industry due to their unique properties, in particular good stability to environmental effects, good physical-chemical and elastic characteristics, chemical and ozone-stability, radiation, oils, acids and alkalis stability, etc. [78,79,176,207,253]. 

Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. To model this material behavior, viscoelasticity utilizes spring constants ( i and E2), dashpots (viscosity, v), and St. Venant sliders (a slider to account for nonrecoverable deformation) elements. The properties of these elements may be selected to cover a wide range of elastic and time-dependent viscous behavior. Viscoelastic models can be divided into both the number of elements employed and whether the elements are in a series or parallel arrangements. These elements may be linear or nonlinear and are combined as necessary for the model to describe the behavior of the sediment imder study. These models describe short-term behavior reasonably well, but tend to not yield reliable predictions of deformation for extended time periods. 

Figure 4.6 presents the distribution of internal stresses in the epoxy rubber coating determined by the lattice cell method. A feature of the calculation is the large ratio of the length to the width of the specimen, with a substantial difference of the elastic characteristics that characterize the system ...

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