When an elastomeric material is deformed and subjected to temperatures above some characteristic value Tcr (near 100o 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 constitutive theory that accounts for this temperature dependent microstructural change is used to study the influence of these changes on the inflation of a spherical elastomeric membrane. The membrane is first inflated to a fixed new radius while at a temperature below Tcr. While at this fixed radius, the temperature is increased above Tcr for a period of time during which there is scission and re-crosslinking. The temperature is subsequently reduced to its original value, and the membrane now has a substantially modified pressure-radius relation and a new radius at zero pressure. These depend on the individual network material properties, the pre-scission inflated radius and scission kinetics. Numerical examples are presented for elastomeric networks that can be modeled as Mooney-Rivlin materials.
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