The Different Types of Mechanical Behaviour

It is difficult to classify polymers as particular types of materials such as a glassy solid or a viscous liquid, since their mechanical properties are so dependent on the conditions of testing, for example the rate of application of load, temperature and amount of strain. 

A polymer can show all the features of a glassy, brittle solid or an elastic rubber or a viscous liquid depending on the temperature and time scale of measurement. Polymers are usually described as viscoelastic materials, a generic term which emphasises their intermediate position between viscous liquids and elastic solids. At low temperatures, or high frequencies of measurement, a polymer may be glass-like with a Young s modulus 

Mechanical Properties of Solid Polymers, Third Edition. I. M. Ward and J. Sweeney. 2013 John Wiley Sons, Ltd. Published 2013 by Jdin Wley Sons, Ltd. 

It is usual to discuss the mechanical properties in the different temperature ranges separately, because different approaches and mathematical formalisms are adopted for the different features of mechanical behaviour. This conventional treatment will be followed here, although it is recognised that it somewhat arbitrarily isolates particular facets of the mechanical properties of polymers. 

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