Strain localization and failure initiation in cylindrical aluminum tubes subjected to radial impulse loading

In this study, we examine strain localization and failure initiation in cylindrical aluminum tubes subjected to radial impulse loading. This thesis is divided into two parts: the first part explores strain localization in aluminum 6061-T6 tubes undergoing radial expansion. An electromagnetically induced body force is used to expand a total of six tube specimens with varying body force intensities. The experimental response of the tube specimen is obtained by capturing images at different times of the expansion via a high-speed camera and conical mirror. A time history of the tube radius and global hoop strain is acquired by fitting the images of the tube with best fit circles using an iterative least-squares approach. For one specimen digital image correlation is implemented in addition to the circle fitting as a means of tracking the local true strain with time. Postmortem observations of the tube specimens reveal a localization pattern different than those found in previous studies that examined aluminum 6061-O tubes. An argument is made that Joule heating and thermal softening contribute to the unique localization pattern. Two numerical models, with differing magnitudes of thermal softening, are constructed to understand the observed localization. At the end of the chapter, proposals for future investigations are presented. The second chapter is devoted to buckling and fracture of an aluminum 7075-T73 tube exposed to a compressive impulse. A numerical model is constructed to analyze the development of fracture nucleation and propagation. Element failure is modeled with the Johnson-Cook damage criterion. Fracture in the walls of buckled cylindrical tubes appears to be a topic not addressed in previous literature. Nodal data and contour plots of the model are used to construct a general case for the response mechanism leading to fracture. Numerical results are compared to previous experimental investigations. Finally, proposals for future experimental examinations of fracture in buckled cylindrical tubes are provided.