Boltzmann Superposition Principle in Creep Experiments

Let us assume further that the perturbation decreases Aa(03) at f = 03. In this case, the system interprets this effect as if a stress — Act(03) were applied to the material at time 0s. In that case the shear strain can be written as 

The relationship between the shear strain and the shear stress can be 

This equation, one of many possible forms of expressing the Boltzmann superposition principle, indicates that the effects of mechanical history are linearly additive (12,13). 

Since the shear stress is canceled at t = 0, the shear strain at t 0 is expressed by (7) 

By making the change of variables t — Q = u in this equation, the elastic contribution to the strain, u units of time after the stress is canceled, can be written as 

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