Effects of aspect ratio and axial tensile load on the long balloon inflation

Although the localized bulging of long cylindrical tubes has been extensively studied experimentally and analytically, there is a lack of investigation on the deformation of short and moderate-length tubes. Here we study the snap-through instability of a hyper-elastic cylindrical tube under inflation, focusing on how the aspect ratio of the tube and additional axial tensile loads affect the bulging shape profile and initiation pressure. First, we conduct bulging experiments using latex rubber tubes by varying the length-to-diameter aspect ratio and additional tensile load. Additionally, we perform finite element simulations with various geometries and loading and theoretical analyses of an infinite-length tube. Through the simulations, we investigate the critical aspect ratio of the tube that divides the bulging mode into two modes: whole bulging of short tubes and localized bulging of long tubes. The experimental and simulation results show that the initiation pressure decreases and converges as the aspect ratio and axial tensile load increase. Furthermore, we find that axial tension greater than the shear modulus prevents snap-through in short tubes and negates the effects of aspect ratio on the initiation pressure. We believe that the results of this study can provide insights into controlling the bulging mode and initiation pressure in tube-like soft devices, such as soft pneumatic actuators and energy harvesters.