DEVELOPMENT, VERIFICATION, AND VALIDATION OF AN APPLIED ELEMENT METHOD SIMULATION FRAMEWORK FOR GLASS LITE FRACTURE, FRAGMENTATION, AND DEBRIS FIELD PREDICTION
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Abstract
In the aftermath of an explosive event, forensic investigators are presented the challenge of characterizing the properties of the explosive device, including the charge size and epicenter of the detonation. Although surrounding infrastructure damaged during the explosion serves as witness to the event, evidence in the form of structural damage is conventionally relegated to a qualitative analysis in favor of nonstructural evidence, such as blast residue, primarily because of the difficulty associated with accurately predicting nonlinear structural behavior under blast loading. Further, simulation of debris field formation potentially resulting from fragmentation of windows, which are commonly observed to fail during blast events, is beyond the conventional capabilities of most numerical methods for structural dynamics simulation. The primary objective of this research effort is to develop a physics-based simulation tool that is specifically capable of predicting the distribution of glass debris fields generated during blast events. Toward achieving this stated objective, a simulation framework for predicting glass lite failure probabilities and debris fields under blast loading is developed through implementation and extension of the relatively new Applied Element Method of structural analysis. Although similar to the Finite Element Method, the Applied Element Method has been demonstrated in existing literature as advantageous for simulation of complex, nonlinear structural behavior, including progressive collapse, fracture, fragmentation, and formation of debris fields, because of its unique approach to element connectivity. Development of the simulation framework is accomplished in four distinct phases involving verification and validation of software routines developed for simulating linear elastic static and dynamic behavior, nonlinear geometric behavior, nonlinear material constitutive behavior, and particle dynamics with element contact behavior. The predictive fidelity of the developed simulation framework for problems involving linear elastic behavior and nonlinear geometric effects is successfully verified through comparison to analytical and Finite Element models. Validation of the predictive fidelity of the simulator for problems involving complex nonlinear behavior, including fracture, fragmentation, and debris field formation, is accomplished through comparison with experimental results compiled specifically for this research effort. The experimental test program includes six open-arena blast tests performed with a small enclosure featuring a conventional fenestration system outfitted with six conventional tempered glass lite specimens. Experimental characterization of the glass lite behavior was also performed through extensive experimental modal analysis and through uniform static loading to failure of a glass lite specimen mounted in the fenestration system.In order to accurately predict the failure behavior of the glass lite specimens, the Applied Element Method is extended for the first time to simulate fracture and fragmentation of tempered glass, and, as a further component of this dissertation, is implemented with the well established Glass Failure Prediction Model to predict the failure probabilities of the glass lite specimens under static loading and open-arena blast loading.Finally, implementation of the developed simulation framework to model the experimental scenarios of open-arena blast testing indicates that the Applied Element Method is capable of predicting debris field distributions that exhibit strong qualitative agreement with the observed experimental results.