Alternative models nucleation-controlled mechanisms

In the Eyring approach, stress affects the rate at which deformation occurs in a continuous manner. Although there is zero strain rate at zero stress, any non-zero value of stress, however small, gives rise to plastic deformation. The application of the stress speeds up the processes that are essentially ever-present, until the stress associated with them is equal to the applied stress the deformation is referred to as being velocity-controlled. 

There is another class of model in which the deformation is referred to as nucleation-controlled. Here, the applied stress is assumed to induce specific physical events, without which deformation cannot proceed. An example of such a model is that due to Argon [27]. He envisaged that shear strain was associated with buckling of the polymer chain via the action of a pair of opposed kinks. As pointed out by Ward [28], it is difficult to distinguish between the Argon and Eyring models by mechanical experimentation. 

When considering the interactions between chains in a deforming polymer we may envisage a number of feasible deformation mechanisms the richness of possibilities will depend on the complexity of the molecular chains. Recently, 

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