There have been some studies reported in the literature involving the pressure waves generated during the implosion process. Turner [3] conducted experiments with thin-wall glass spheres to determine the influence of failure mechanisms on pressure waves. He concluded that the computational model of an underwater implosion event must include the structure that separates the low pressure air from the high pressure water. If the structure is neglected, the model will over predict the peak pressure. Later, Turner and Ambrico [4] conducted near-field pressure wave measurements from an imploding cylinder and used a fluid–structure interaction finite-element methodology to predict the dynamic pressure history and the collapse mechanics during implosion. Ikeda [5] studied the implosion of aluminum cylindrical shell structures in a high-pressure water environment. It was reported that the pressure time history at a certain distance scales well with time and pressure scales from cavitation bubble collapse theory. Ikeda [6] also studied the explosion induced implosion of cylindrical shell structures in high-pressure environments. It was found in the study that the implosion is induced by two mechanisms: the shockwave generated by the explosion and the jet formed during the explosion-bubble collapse. There is limited literature available itself on the implosion of structures in free-field and, to the best of the authors’ knowledge, no studies have been reported on the collapse of a tube within a closed environment. This study will investigate the implosion of a tube occurring within a confining tube (a closed environment). Unlike the free-field implosion experiments where the hydrostatic pressure is maintained in the surrounding environment during the collapse process, these experiments were conducted with implodable volumes inside a constant volume of pressurized water. 40.2 Specimen Details Implodable volumes used in this study were made out of aluminum 6061-T6 cylindrical tubing. After cutting to the desired length of the tube, the ends of the implodable volume were sealed on both ends using caps. End-caps were made out of same material, aluminum 6061-T6, and circumferential o-rings were used to ensure proper sealing at the ends. Table 40.1 shows a layout of experiments conducted during this study. The length of the four implodables was held constant (304.8 mm) and the diameters were increased from 38.1 mm (1.500) to 101.6 mm (4.000). The wall thickness was also increased along with the diameter to keep the critical collapse pressure approximately constant. A three-spoke fixture was utilized to hold the implodable volumes concentrically within the outer tube. A schematic of the fixture with the specimen is shown in Fig. 40.1. Table 40.1 Layout of the experiments Geometry no. Wall thickness Outer diameter L/D ratio Collapse pressure MPa (psi) 1 0.89 mm (0.03500) 38.1 mm (1.500) 8 325 psi 2 1.24 mm (0.04900) 50.8 mm (2.000) 6 515 psi 3 1.65 mm (0.06500) 76.2 mm (3.000) 4 510 psi 4 1.65 mm (0.06500) 101.6 mm (4.000) 3 370 psi Fig. 40.1 Three-spoke fixture for implodable volume 328 S. Gupta et al.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==