Models of spherulite deformation taking into account changes in volume

A general method is presented for taking into account changes in volume in several types of calculations concerned with spherulite deformation in semicrystalline polymers. The method is applicable at large strains for which the low‐strain limiting form of the equation defining Poisson's ratio is no longer valid. Applications are made to calculations of the three crystal orientation functions for models of spherulite deformation based on those proposed by Wilchinsky, Stein et al., and Oda et al. The effects of changes in volume are considered in detail and are compared with previous results in which the volume change was neglected. Calculations of spherulite birefringence are considered in a similar manner, as are the equations for determining spherulite deformation by means of low‐angle light‐scattering measurements. Results indicate that in several cases details of deformation mechanisms previously proposed should be revised in light of the effect of the change in volume on the calculated orientation functions. The equations in each case are presented in terms of a parameter β, the square root of the third strain invariant of the deformation tensor. Results are presented in numerical form for many of the basic parameters. Equations for all such results are expressed in explicit form and, in most cases, are displayed graphically together with available experimental data.