with xðsÞ denoting the position of a generic particle P at time s 2 ½0; t, and X its position at the initial reference time. Note
that the start time of the motion, and any imposed tractions, will be taken as t ¼ 0. The quantity J ¼ det F, expressing the
local volume change, is a constant J ¼ 1 when the deformation is isochoric. Let us assume that the material is isotropic
and therefore from the deformation gradient tensor F we obtain the right Cauchy-Green tensor C ¼ FTF, and its principal
invariants