Relaxation time and its distribution

In order to relate viscoelasticity to processability, it helps to understand the concept of relaxation time. The definition of relaxation time customarily uses a spring and dashpot 

Starting with a situation, where a stimulus is given to a system to excite it, the extent of the excitation is expressed by C. If the system is allowed to return to the ground state spontaneously, the rate -dC /dt is proportional to the extent of excitation, C.  

The integration of this equation gives a well-known equation. 

This equation is for the first order reaction in chemical kinetics. It is also the equation for the decay of radioisotopes in physics. In viscoelasticity 

In the field of viscoelasticity there is retardation time and relaxation time. Qualitatively these terms may be understood by analogy to human behaviour. 

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