A study of the collapse loading of spherical shells.

Current arms control agreements have provided the impetus for national directives to cease production of new strategic weapons and to end nuclear testing. This has placed a tremendous burden on the national laboratories for assuring stockpile certification. The Stockpile Stewardship Program's fundamental objective within the Department of Energy (DOE) is to maintain a high confidence in the safety, reliability, and performance of the existing U.S. nuclear weapons stockpile. As such, enhanced evaluation capabilities are needed to quantify the effect of possible anomalies that may arise in a weapon (e.g., due to aging mechanisms), and assess its performance, safety and overall reliability. Validated numerical methods must be employed in determining the reliability of specific weapon components, including the overall weapon system. The validated numerical models must, however, be based on accurate information of each component's geometry and material properties in an aged condition. Once these variables are known, extrapolation of potential lifetime of the weapon can be determined with some level of confidence. The goal is to develop an engineering capability that provides a reliability-based structural evaluation technique for performing weapon reliability assessments. To enhance the analyst's confidence with these new methods, an integrated experiment and analysis project has been developed.more » The focus of this project is to generate accurate probabilistic structural response simulations using numerical models of commercially available, stainless steel spherical marine floats, under collapse loads, and compare with experimental results. The spherical marine float geometry was chosen because of its simple shape, yet highly complex nonlinear deformation behavior, leading to complex states-of-stress. There is also a variability associated with geometry and mechanical properties of commercially available (i.e., off-the-shelf) marine floats. The variability is not uncommon, and principally due to numerous forming processes, different operators, etc., which bulk production operations employ for a single material lot. The probabilistic analysis is performed using the NESSUS probabilistic analysis software. NESSUS simulates uncertainties in loads, geometry, material behavior, and other user-defined uncertainty inputs to compute reliability and probabilistic sensitivity measures. To facilitate analyses of a broad range of problem types, a large number of efficient and accurate probabilistic methods are included in NESSUS. The probabilistic validation of the current work is performed in two phases. Initially, the deterministic spherical marine float model is validated against the experimentally observed collapse load. Next, variations in geometric shape parameters (i.e., surface geometry and thickness) are characterized using random fields to quantify test data from actual float geometry. Uncertainties in material properties (i.e., stiffness, strength, and flow) are also included in the probabilistic model. Finally, the probabilistic numerical model is validated by comparison to the predicted and observed variation in collapse load.« less