Torsion of an elastomeric cylinder undergoing microstructural changes

A constitutive theory which accounts for scission and cross linking process es in polymers during deformation is used to analyze the torsion of a circu lar bar. In each increment of deformation at a material element of the tors ion bar, some volume fraction of material undergoes scission and then re-cr oss links to form a new network with a new reference state. The scission pr ocess reduces the ability of the material to transmit stress. The newly for med networks restore the ability of the material to transmit stress. The to tal stress is assumed to be the superposition of the stress in the remainde r of the original material, determined by its deformation from its original configuration, and the stress in each newly formed network, determined by the deformation in that network from the configuration at which it formed. The interaction of this material response with the inhomogeneous deformatio n during torsion is studied. The analysis shows the evolution of regions of original and modified material, the softening effects associated with the process of scission and re-cross linking and the occurrence of residual str ess and deformation on removal of load.