Thermal extrusion of a non-linear viscoelastic solid inside a long cylindrical tube

Abstract

An analysis is presented for the axial extrusion of an expanding viscoelastic solid inside a long cylindrical tube. Both differential thermal expansion and expansion of gas bubbles in the solid are considered as driving mechanisms. Finite element calculations are used to illustrate the details of the behavior of the system. The response is shown to be initially elastic followed by the development of a boundary layer near the free surface where the pressure gradients are sufficiently large to cause axial viscous flow. Simple boundary layer equations are derived to describe this flow. Results using these equations agree well with the results of the finite element calculations. The theory is applied to the extrusion of uranium-based metallic reactor fuel during overheating transients.