Mechanical Models, Relaxation and Retardation Time Spectra

3 Mechanical models, retardation and relaxation time spectra 

The total stress o is shared between spring and dashpot a = a + 02, but the strain in each component is the total strain e = e = C2. 

It is convenient in creep experiments to replace k by 1/J, where J is the spring compliance, to give 

The retardation time t is the time after loading for the strain to reach 

The Kelvin model is unable to describe stress relaxation, as at constant strain the dashpot cannot relax. In mathematical terms AelAt) = 0, giving o = E e. 

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