When an elastomeric material is deformed and subjected to temperatures above some characteristic value Tcr (near 100 degrees C for natural rubber), its macromolecular structure undergoes time and temperature dependent chemical changes. The macromolecular chains and crosslinks undergo scission, and then recoil and re-crosslink to form new networks with new reference configurations. The resultant material system consists of multiple macromolecular networks, each with its own reference configuration. The process continues until the temperature decreases below Tcr. Compared to the virgin material, the new material system has modified properties (reduced stiffness) and permanent set on removal of the applied load.
A new constitutive theory is used to study the influence of the changes of macromolecular structure on the torsion of an initially homogenous elastomeric cylinder. The cylinder is held at its initial length and given a fixed twist while at a temperature below Tcr. The deformation is held fixed and the temperature of outer radial surface is increased above Tcr for a while and then returned to its original value. Assuming radial heat conduction, material elements undergo different scission and re-crosslinking histories. After enough time has elapsed such that the temperature field is again uniform and at its initial value, the cylinder properties are now inhomogeneous. Assuming the elastomeric networks to act as Mooney-Rivlin materials, expressions are developed for the permanent twist on release of torque and the new torsional stiffness in terms of the scission kinetics.
Back to Horgan Symposium
Back to SES Abstracts
Back to The 41st Annual SES Technical Meeting