Heat effect, Gough-Joule

Physically, the temperature rise in a lament must be due to a combination of viscous dissipation and elastic (i.e., entropic) heating the Gough-Joule effect.(D The former is no doubt dominant in the case of fracture of high polymers(40) see below. But it is not possible at present to estimate the proportions of these two causal factors. It is to be expected that their... 

Gough-Joule effect When an elastomer/ rubber is stretched adiabatically (without heat entering or leaving the system), heat is evolved, This effect was first reported discovered by Gough in 1805 and rediscovered by Joule in 1859. 

An apparatus which demonstrates the Gough-Joule effect. It comprises a pendulum adjusted so that a rubber sample is under stretch. Heat from a lamp causes the rubber to contract and swing the pendulum. This pulls the rubber into a shaded section where it extends and moves the pendulum back to the original position, whereupon the cycle is repeated. 

The Gough Joule effect, shown as an increase in modulus with an increase in temperature and the retraction of stressed rubber on heating An ability of some elastomers to undergo strain-induced crystallization The susceptibility of un.saturated rubbers to ozone attack and subsequent cracking in the stretched state... 

Moreover, rubbers exhibit unique thermo-elastic effects unknown in metals, as noted first by Gough as early as 1805. Gough (1805) reported two distinctive responses, namely that (a) a rubber when held stretched under a constant force contracts reversibly on heating, and (b) it gives off heat reversibly when stretched at constant temperature (Treloar 1975). These important characteristics that were confirmed later by Joule (1859) are now referred to as the Gough-Joule effect and are key in the mechanistic understanding of the elastic behavior of rubbers. 

Fig. 3.5 Illustration of the experiment demonstrating the Gough-Joule effects. The light will heat the rubber strip, increases the latter s elastic modulus and then decreases the displayed weight in the electronic balance. Switched-off the light, the displayed weight will be gradually recovered...

A unique quality of rubber is the Gough-Joule effect. Unlike other materials, when rubber is stretched rapidly it heats up. If rubber is stretched under a load, it will retract as the temperature is raised and it is held at the other end. 

Finally, we turn from solutions to the bulk state of amorphous polymers, specifically the thermoelastic properties of the rubbery state. The contrasting behavior of rubber, as compared with other solids, such as the temperature decrease upon adiabatic extension, the contraction upon heating under load, and the positive temperature coefficient of stress under constant elongation, had been observed in the nineteenth century by Gough and Joule. The latter was able to interpret these experiments in terms of the second law of thermodynamics, which revealed the connection between the different phenomena observed. One could conclude the primary effect to be a reduction of entropy... 

Gough, in 1805, established that raw rubber becomes warm on being stretched and contracts on being heated. Page, in 1847, and Joule, in 1857, independently reported similar observations. Joule s observations were more quantitative in nature and the aforesaid effect is hence referred to as Joule s effect [6]. 

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