respectively, so that the first three principal invariants of C are I1 ¼ I2 ¼ 3 þ k2
; I3 ¼ 1.
Let us assume that kðtÞ is such that inertial effects can be neglected; therefore this homogeneous deformation automatically
satisfies the equations of motion (equilibrium). As stated earlier, this requires an assumption on the relationship
between the shear and the relaxation timescales of the material. The resulting components of stress are, after some algebra,
given by T13ðtÞ ¼ T23ðtÞ ¼ 0 and