An experimental study of localized bulging in inflated cylindrical tubes guided by newly emerged analytical results

Abstract

An experimental study is conducted on localized bulging of inflated latex rubber tubes of a range of wall thicknesses and tube lengths, guided by newly emerged analytical results. In the case when the tube has one free closed end that may or may not be subjected to a dead weight, the initiation pressure for localized bulging is determined by a bifurcation condition, and the propagation pressure is determined by Maxwell’s equal-area rule. It is shown that after bulge initiation the pressure will decrease monotonically towards, but will never reach, the propagation pressure, and it is when the pressure is sufficiently close to this propagation pressure that rapid propagation of the bulge in the axial direction takes place. It is found that the experimentally observed initiation pressure is around 15% below the theoretical prediction, which is consistent with the fact that bulging initiation is a sub-critical phenomenon and is therefore sensitive to imperfections. The experimentally observed propagation pressure is always very close to the theoretical prediction, which confirms the insensitivity of this pressure to imperfections and demonstrates the predictive power of the material model fitted from our own experiments on equibiaxial stretching. In the other case when the tube is first stretched and then fixed at both ends, bulge initiation takes place in the same manner as in the previous case, but the propagation pressure is no longer determined by Maxwell’s equal-area rule. After bulge initiation the pressure will first decrease to a minimum and then rises slowly, and it is on the latter ascending path that the bulge starts to propagate rapidly in the axial direction. A semi-analytical method is proposed for the determination of the minimum pressure. Numerical simulations with the use of the software Abaqus are also conducted to verify the theoretical predictions.