Browsing by Subject "Honeycomb"
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Item Experimental study of impact loading on negative stiffness structures(2015-05) Bostwick, Kenneth Stanley; Seepersad, Carolyn C.; Haberman, Michael R.; Wilson, Preston SThis work outlines the design of a drop testing apparatus and the use of the apparatus to perform impact tests on negative stiffness honeycomb structures. Negative stiffness beams are non-linear spring elements that can be used to absorb energy. When prefabricated negative stiffness beams are arranged together in a periodic pattern they create an energy absorbing honeycomb material that can recover from large deformations. Negative stiffness honeycombs have been shown to function similarly to regular honeycombs during quasi-static loading, but are largely untested for impact loading. Two types of honeycomb designs--referred to as vertical and horizontal arrays--have been designed and fabricated to experimentally determine their performance when subjected to impact loading. The performance of each array is compared using finite element models (FEM), quasi-static tests, and drop tests. A drop test apparatus is constructed to perform the impact testing, by measuring the acceleration profile of a mass released from variable drop heights. Results indicate that vertical and horizontal honeycombs reduce accelerations by at least 85 percent when compared to impact without the presence of a honeycomb.Item High performance façades for commercial buildings(2010-05) Bader, Stefan; Lang, Werner X.; Novoselac, Atila; Moore, Steven A.; Beaman, Michael; Whitsett, DasonDue to the fact that construction, maintenance and operation of buildings consume almost 50% of the energy today, architects play a major role in the reduction of energy consumption. The building’s envelope (façades and roof) can have a significant and measurable impact. With regard to overheating and the potential lost of internal heat, transparent parts of the building envelope have a large effect on the building’s energy consumption. Modern, transparent façade systems can fulfill contemporary demands, such as energy conservation, energy production or the degree of visual contact, of sustainable buildings in order to reduce internal heating, cooling, and electrical loads. An analysis of existing shading devices and façade design leads to a comparative analysis of conventional shading devices like horizontal and vertical blinds as well as eggcrate and honeycomb shading structures in a hot-humid climate like Austin, Texas. This study helped evaluating strengths and weaknesses of each device resulting in an optimization process of conventional shading devices. Ultimately, an optimized shading structure has been developed. This project aimed to develop an advanced transparent façade system for a south-oriented commercial façade in Austin, Texas, which fulfills high standards with regard to low energy use, by limiting cooling loads and demands for artificial lighting while avoiding glare and heat losses during the cold season. The optimization has been achieved in providing full shading for a specified period of time throughout the year while providing maximized solar exposure. The shading structure consists out of an array of fixed shading components varying in size and proportion to fulfill criteria like specific views, transparency and aesthetics. The shading structure has been compared to conventional shading devices and analyzed with regard to the reduction of annual solar radiation. The improvement in design and energy consumption contributes to the variety of shading structures for building skins. It is anticipated that the solutions will help to widen the options for aesthetically pleasing, high-performance façades for commercial buildings.Item On the crushing of honeycomb under axial compression(2010-12) Wilbert, Adrien; Kyriakides, S.; Ravi-Chandar, KrishnaswamyThis thesis presents a comprehensive study of the compressive response of hexagonal honeycomb panels from the initial elastic regime to a fully crushed state. Expanded aluminum alloy honeycomb panels with a cell size of 0.375 in (9.53 mm), a relative density of 0.026, and a height of 0.625 in (15.9 mm) are laterally compressed quasi statically between rigid platens under displacement control. The cells buckle elastically and collapse at a higher stress due to inelastic action. Deformation then first localizes at mid-height and the cells crush by progressive formation of folds; associated with each fold family is a stress undulation. The response densifies when the whole panel height is consumed by folds. The buckling, collapse, and crushing events are simulated numerically using finite element models involving periodic domains of a single or several characteristic cells. The models idealize the microstructure as hexagonal, with double walls in one direction. The nonlinear behavior is initiated by elastic buckling while inelastic collapse that leads to the localization observed in the experiments occurs at a significantly higher load. The collapse stress is found to be mildly sensitive to various problem imperfections. For the particular honeycomb studied, the collapse stress is 67% higher than the buckling stress. It was also shown that all aspects of the compressive behavior can be reproduced numerically using periodic domains with a fine mesh capable of capturing the complexity of the folds. The calculated buckling stress is reduced when considering periodic square domains as the compatibility of the buckles between neighboring cells tends to make the structure more compliant. The mode consisting of three half waves is observed in every simulation but its amplitude is seen to be accented at the center of the domains. The calculated crushing response is shown to better resemble measured ones when a 4x4 cell domain is used, which is smoother and reproduces decays in the amplitude of load peaks. However, the average crushing stress can be captured with engineering accuracy even from a single cell domain.