The discrete relaxation time spectrum can be extracted by fitting following model with n user selectable terms from the creep or recovery compliance (J(t), Jr(t)).
The spectrum represents all the pairs of fitted {Ji,ti} parameters and can be extracted into a new file if desired.
Use this model to extract the Retardation time spectrum. The Retardation time spectrum is used to interconvert linear viscoelastic material functions such as J’, J” to J(t); G’, G” to J(t); etc.
The calculation of the Relaxation Time Spectrum from experimental data is an ill-posed problem, in that small differences in the data can result in large differences in the spectra. Sophisticated mathematical techniques, such as the regularization technique are used to counter this problem.
A special case of the discrete Retardation time spectrum is for n=1, or one single term to describe the viscoelastic response. This is the Berger model. The Berger model consists of the instantaneous compliance Jo, a single term viscoelastic component J(t) and the flow term t/ho.
