Deformation elastomers

Basically, four types of tensile stress-strain curve are found for cross-linked elastomers deformed below Tg. These are shown schematically in Fig. 20 where pre-... 

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,... 

Mao Y, Terentjev EM, Warner M. 2001. Cholesteric elastomers deformable photonic solids. Phys Rev E 64 041803. 

Load Fracture. Thermoplastics, thermosets, and elastomers deform in different ways. In the case of ductile thermoplastics, as the load increases, the tangled, thread-like macromolecules become stretched, aligned, and in some cases will glide apart. The stretched areas will recoil like a spring, and this will be most pronounced at the highly stressed fracture site, which additionally warms up on... 

Abrasion resistance is another complex area. One of the reasons for confusion is that the various test methods do not agree well with each other. There is a perception that hard surfaces lead to the best abrasion resistance, however, that does not jibe with the facts. In actuality, it is elastomeric surfaces that have excellent abrasion resistance. Look, for example, at rubber car tires and PVC flooring, which is always coaled with a polyurethane elastomer layer to provide wear resistance. Elastomers deform and spring back undamaged, so scratch and wear resistance is good [17]. 

It is worthwhile taking note of their Important results, because they are relevant to the friction of elastomers. Moreover,there Is no experimental work available on the details of surface topography of elastomers. Since elastomers deform even under very light loads, it is not easy to measure the topographical features. 

The properties of elastomeric materials are controlled by their molecular structure which has been discussed earlier (Section 4.5). They are basically all amorphous polymers above their glass transition and normally crosslinked. Their unique deformation behaviour has fascinated scientists for many years and there are even reports of investigations into the deformation of natural rubber from the beginning of the nineteeth century. Elastomer deformation is particularly amenable to analysis using thermodynamics, as an elastomer behaves essentially as an entropy spring . It is even possible to derive the form of the basic stress-strain relationship from first principles by considering the statistical thermodynamic behaviour of the molecular network. 

It is apparent from considerations of the structure in Section 4.2 that semi-crystalline polymers are essentially two-phase materials and that the increase in modulus is due to the presence of the crystals. Traditional ideas of the stiffening effect due to the presence of crystals were based upon the statistical theory of elastomer deformation (Section 5.3.2). It was thought that the crystals in the amorphous rubber behaved like crosslinks and produced the stiffening through an increase in crosslink density rather than through their own inherent stiffness. Although this mechanism may be relevant at very low degrees of crystallinity it is clear that most semi-... 

The isothermal reversible work of deformation w per unit volume of an elastomer is given by the statistical theory of elastomer deformation as... 

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