RATE-DEPENDENT RELAXATION SPECTRA AND THEIR DETERMINATION

Stress overshoot at the start of a flow, stress relaxation after the stoppage of a flow, and superposition of a small oscillation upon a steady shear flow are treated by the use of the concept of a deformation rate-dependent relaxation spectra. These analyses are used as the basis of methods to determine the spectrum of relaxation times. Although the treatment is restricted to specific types of constitutive equations in which the response function depends on the rate of deformation invariants, it is not necessary to specify any functional form of the response function.