Elastomer deformation tension

In equation (6-1) the increment of work, dW, refers to all of the work (i.e., electrical, mechanical, pressure-volume, chemical, etc.) performed by the system (the sample) on its surroundings. The development of thermodynamics given in most physical chemistry texts is confined to gases where d W becomes simply pressure-volume work, PdV, where P is the external environment. In the case of an elastomer deformed by an amount dL in tension and exerting a restoring force f the mechanical work performed on the system to accomplish the deformation, namely fdL, must also be included in dW. Thus, for an elastomer strained uni axially in tension,... 

When there is no volume change, as when an elastomer is stretched, Poisson s ratio is 0.5. This value decreases as the Tg of the polymer increases and approaches 0.3 for rigid solids such as PVC and ebonite. For simplicity, the polymers dealt with here will be considered to be isotropic viscoelastic solids with a Poisson s ratio of 0.5, and only deformations in tension and shear will be considered. Thus, a shear modulus (G) will usually be used in place of Young s modulus of elasticity E Equation 14.2) where E is about 2.6G at temperatures below Tg. 

Although traditionally the thermodynamic treatment of the deformation of elastomers has been centered on the force, the alternative condition of keeping the force (or tension) constant and recording the sample length as a function of temperature at constant pressure is even simpler 23,271. 

The property of elastic recovery of rubbers allows them to be used for many products which are subjected to deformation, whether by tension or compression, and must not be destroyed by such forces. Abrasion and corrosion resistances are often the main properties in choosing an elastomer-based product over alternative products. In the mineral processing industry, abrasion often results from a... 

The engineering property that is of interest for most of these applications, the modulus of elasticity, is the ratio of unit stress to corresponding unit strain in tension, compression, or shear. For rigid engineering materials, unique values are characteristic over the useful stress and temperature ranges of the material. This is not true of natural and synthetic rubbers. In particular, for sinusoidal deformations at small strains under essentially isothermal conditions, elastomers approximate a linear viscoelastic... 

Equation 11.41 describes the engineering (nominal) stress a on an elastomer as a function of its draw ratio X. The measure of deformation that is most commonly used by engineers, the engineering (nominal) strain , equals (X-l). Under uniaxial tension, it describes the fraction by which a specimen has been extended relative to its initial (undeformed) dimensions. 

Different cross-Unking systems influence selected properties of elastomers and duroplastics. So far the reaction kinetics influence the induction time, the activation energy, and the cross-linking rate. Cross-linking effects influence the density and the chemical stracture. And the cross-Unking system has an influence on the foUowing properties tension- and residential deformation, dynamic properties, thermal stabUity, and chemical resistance. 

The high elasticity or rubber elasticity is a specific state of matter displayed by polymers Large reversible deformation is caused by small tensions. For instance, natural rubber can be stretched reversibly 10-15 times of its original length. Polymeric materials exhibiting high elasticity at room temperature are called elastomers or rubbers. 

A thermoplastic elastomer (TPE) is a rubbery material with properties and functional performance very similar to those of a conventional thermoset rubber, yet it can be fabricated in the molten state as a thermoplastic. ASTM D 1566 defines TPEs as a diverse family of rubber-like materials that, unlike conventional vulcanized rubbers, can be processed and recycled like thermoplastic materials. Many TPEs meet the standard ASTM definition of a rubber, since they recover quickly and forcibly from large deformations, they can be elongated by more than 100 percent, their tension set is less than 50 percent, and they are sometimes insoluble in boiling organic solvents. Figure 4.35 indicates hardness ranges for various types of TPEs and conventional elastomers. 

Under the conditions of mechanical solicitation, firstly are split the most tensioned bond between particles that behave as authentic centres of crosslinking, which should be assimilated to the knots of chemical bonds subsequently these ones do not contribute to the material resistance,when exposed to the subsequent solicitation. In this case, the chains distribution between the particles is not statistic one, since the weakened bonds have been split. At high temperatures, the scissions of and remakes of the chemical bond occur in the elastomer network. Consequently, after a certain period the chains distribution will regain its statistic character and the split chains during the first stressing period are replaced with other ones identical. Therefore, a recovering of the modulus to the initial values is expected. However, at small deformations and especially in the case of a poor dispersion of the particles, a decay of modulus is recorded, which was not recuperated during the elastomer thermal treatment. 

It was also established that the black carbon particles included in the elastomer matrix show a different behavior as a function of deformation [1202]. It is assumed that the tensions relaxation in reinforced rubbers, which represents a energy dissipation at high deformations, is not associated with any change of rubber-particles bonds, and it should by explained only by the modifications occurring in the highly elastic phase. Generally, the vulcanised or non-vulcanised elastomers present a common feature, namely to reach... 

Where, d is the particle diameter, v is the interfacial tension, and (T is the stress applied on the particle. The capillary number describes the balance between two simultaneous stresses such as the deforming and restoring stresses acting simultaneously on the droplet. However, this treatment is applicable to Newtonian liquids. Anyway, the general trend is expected to be applicable for viscoelastic material. In the case of viscoelastic polymer blend the deviation is expected as it is no more Newtonian fluid. The strategy for getting microfibrills is to have a elastomer as the matrix... 

G Sell Ch, Bai S L and Hiver J M (2004) Polypropylene/polyainide 6/polyethyleue-octene elastomer blends. Part 2 Volume dilatation during plastic deformation under uniaxial tension. Polymer 45 5785-5792. 

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