The Eyring Equal on

The equation above is equivalent to Equation (7.5) describing the frequency of a molecular event, but here we use Boltzmann s constant k rather than the gas constant R as we are interested in the absolute number of molecular events rather than the overall effect of a mole of material. 

An applied stress a is assumed to produce linear shifts /3a of the energy barriers in a symmetrical way (Eigure 11.11), where /3 has the dimensions of volume. The flow in the direction of the applied stress is then given by 

The resemblance of the large bracket to the sinh function should be noted. 

Assuming that the net flow in the forward direction is directly related to the rate of change of strain, we have 

The rate of strain Equation (11.32) defines an activated viscosity, which is then incorporated in the dashpot of the standard linear solid model, and leads to a more complicated relationship between stress and strain than that for the linear model. The activated dashpot 

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