  Mechanical instability in a pre-tensioned finite hyperelastic tube subjected
to a slowly increasing internal pressure produces a spatially localized bulge
at a critical pressure. The subsequent fate of the bulge, under continued
inflation, is critically governed by the end-conditions, and the initial
tension in the tube. In a tube with one end fixed and a dead weight attached to
the other freely moving end, the bulge propagates axially at low initial
tension, growing in length and the tube relaxes by extension. Rupture occurs
when the tension is high. In contrast, the bulge formed in a tube, initially
stretched and held fixed at both its ends can buckle or rupture, depending on
the amount of initial tension. Experiments on inflated latex rubber tubes are
presented for different initial tensions and boundary conditions. Failure maps
in the stretch parameter space and in stretch-tension space are constructed, by
extending the theories for bulge formation and buckling analyses to the
experimentally relevant boundary conditions. The fate of the bulge according to
the failure maps deduced from the theory is verified; the underlying
assumptions are critically assessed. It is concluded that buckling provides an
alternate route to relieve the stress built up during inflation. Hence
buckling, when it occurs, is a protective fail safe mechanism against the
rupture of a bulge in an inflated elastic tube.
