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Experimental and numerical simulations of explosive loading on structural components : composite sandwich connections


The extreme loading conditions produced from the detonation of an explosive are severely detrimental to structures and structural components. These effects are amplified when a blast occurs in an enclosed or confined geometry, where reduced ventilation and oblique angles result in extended pulse durations and added reflections of generated pressures. The objective of this dissertation is to develop experimental methodologies and numerical assessment tools to document and simulate failure sequences in composite sandwich connections under simulated internal blast loads. The experimental research was conducted using the UCSD Blast Simulator, a one-of-a- kind system able to simulate explosive events without the use of explosive materials and therefore without the associated fireballs. This is accomplished with an array of high velocity hydraulic actuators driven by a combined high pressure nitrogen/hydraulic energy source. In explosive field testing, video and data from instrumentation is often lost to the destructive nature of the blast environment. The simulator allows for the generation of high fidelity data that documents the response and failure progression in structural members, which in turn lends researchers the ability to develop and test damage mitigation strategies as well as design guidelines for critical infrastructure subject to impulsive loads. First, the development of loading protocols were presented, in which pressures of prolonged durations distributed in multiple directions were achieved through the impact of high strength water filled bladders. These methods were then implemented in the testing of 90 degree composite sandwich joint specimens, which were reacted via adjustable steel gripping fixtures mounted in configurations suitable for impact with the high powered Blast Generators. In an effort to create a numerical model capable of simulating the failure modes observed in the Blast Simulator experiments, a series of individual component tests were conducted to assist in the calibration of finite element material models. The characterization of the CFRP facesheet/balsa wood core sandwich material's failure properties in bending, shear and delamination were documented experimentally and validated numerically using LS-DYNA under both quasi- static and dynamic load rates. Finally, the updated material models were implemented into the simulation of the Composite Joint Tests, which highlight the key mechanisms involved in connection failure and ultimately joint breach. The studies found that failure of the connection structure were functions of the bond strength between the panel facesheets and overlaminate used to adhere the sandwich panels together, strongly coupled with the shear capacity of the individual panel cores. Recommendations for improved joint design were made and suggestions for extrapolation of the developed technologies to larger scale testing were offered

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