No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The research presented in this thesis investigates the mechanical properties of candidate materials that could be used as a skin for a morphing wing. A morphing wing is defined as a wing that changes shape. Although engineers have been designing different morphing wing configurations, there has been limited research investigating materials that could be used as a skin for a morphing wing. Specifically, after investigating the different morphing wing abilities engineers at Virginia Tech are designing, criteria were determined for candidate materials. A suitable skin material for a morphing wing will have to be elastic, flexible, have high recovery, resistant to different weather conditions, resistant to abrasions and chemicals, and have a hardness number high enough to handle the aerodynamic loads of the aircraft while in flight. Using some of the preceding criteria, different materials were selected that are readily available in the commercial market. The materials tested were a type of thermoplastic polyurethanes, copolyester elastomer, shape memory polymer, or woven materials that are made out of elastane yarns. The first study determined the required forces to strain the material in a uniaxial direction. A test stand was designed with a gripping device to hold the material. By grounding one side of the material, the other side of the material was pulled using a winch. Using a force transducer and a string potentiometer the required forces and the amount the material was strained was recorded, respectively. Utilizing the same test stand, the amount the material recovered was also acquired. Also, by measuring how much the material necked the elongation ratio was calculated. The final test determined if the forces "relaxed" after being strained to a stationary position. It was found that each material performed differently, but some materials were definitely better suited for morphing wing material. The materials that were made out of thermoplastic polyurethanes, copolyester elastomer, and shape memory polymer required less force and were able to strain more, when compared to the woven materials. The second study determined if the material could be strained in a biaxial direction. The reason for this was for a better understand how the material would perform if the material was strained to an extreme condition. A test stand was designed using the same principles and components as the uniaxial test stand. The only difference was additional sensors were required to measure the force and strain along the other axis. Although a recovery analysis was warranted for the biaxial experiments, most of the materials test failed while being strained a small amount. Also, the material strained a lot less before ripping, when compared to the straining capabilities when only being strained in the uniaxial direction. After conducting the experiments, the results were similar to the uniaxial experimental results. In terms of required forces to strain the material, the thermoplastic polyurethanes and the copolyester elastomer required less force, when compared to the woven materials. The only advantage of the woven materials was they did not break. The final study determined how much the material deflected while being subjected to a pressure load before breaking. The test stand used an air compressor to supply a pressure load to the material, while a laser vibrometer measured how much the material deflected. A regulator was used to control the amount of pressure that was applied to the material. As the pressure load was increased, the material deflected more. The test stand also determined the maximum sustained pressure load the material could handle before breaking. After conducting all the experiments and analyzing the data, it was found woven materials are not suitable as a skin material. The reason air is allowed to pass through the woven material. Therefore, woven materials could not sustain the aerodynamic loads of an aircraft while in flight. The rest of the materials performed differently. Specifically if the material strained well and required less force while conducting the uniaxial and biaxial experiments, those materials could not sustain a high pressure load. Yet, the materials that did not strain well and required more force were able to handle a larger sustained pressure load. / Master of Science

The focus of this research was to quantify the post-fire mechanical properties of 5083-H116 and 6082-T6 aluminum alloys. Post-fire exposure is considered heating the material to a particular temperature then cooling the material back to room temperature. The research included evaluating parent materials as well as welded samples. Post-fire mechanical properties of parent materials were evaluated at temperatures ranging from ambient to 500oC with isothermal and transient heating. Changes in material properties were evaluated through static tensile tests and hardness testing on cooled samples. Using this data, an assessment was performed to investigate the relationship between hardness and mechanical properties. For the alloys evaluated, empirical relationships were found between Vickers hardness and post-fire strength. Testing was also performed on butt welded samples of 6082-T6 exposed isothermally to temperatures ranging from ambient to 500oC. Vickers hardness profiles were measured across a sample to quantify the hardness of the weld, heat affected zone, and parent material. This was performed at room temperature and following different heat exposures. Static tensile tests were used to evaluate the effect of reheating on the welded samples. Post-fire strength of welded samples was strongly affected by weld geometry. Parent material hardness varied with reheating while weld hardness remained constant. At select temperatures, this resulted in the weld having a higher Vickers hardness than the parent material. Despite this tensile failure always occurred within the weld. / Master of Science

No / We have studied the tensile behaviour of polycarbonate at large strains below the glass transition temperature. Experiments have been carried out at a series of constant temperatures and also under conditions of falling temperature. The specimens neck with a natural draw ratio of ~2, and the study focuses mainly on the necked material. Isothermal experiments reveal an elastic mechanism that initiates beyond the natural draw ratio. A model consisting of an Eyring process and two Gaussian elastic mechanisms is shown to be applicable to both the isothermal and anisothermal stress relaxation and stress-strain results. The same model also produces reasonable estimates of the stresses generated during the necking process. In addition, a simple relationship between isothermal and anisothermal stress relaxation is demonstrated.

Yes / The effects of 0·5 wt-%Mo addition on the processing, microstructure, and strength of PM Fe–3·5Mn–0·7C steel are described. Water atomised and sponge irons, Astaloy 1·5Mo, milled ferromanganese, and graphite were the starting powders. During sintering in 75H2 /25N2 or pure hydrogen the dewpoint was controlled and monitored; in particular the effects of improving it from -35 to -60°C were investigated. Faster heating rates (20 K min-1), sufficient gas flowrates, milling the ferro alloy under nitrogen, a low dewpoint (<-60°C), and a getter powder can all contribute to the reduction or prevention of oxidation of the manganese, in particular formation of oxide networks in the sintered steels. For 600 MPa compaction pressure densities up to 7·1 g cm-3 were obtained; these were not significantly affected by sintering at temperatures up to 1180°C. The sintered microstructures were sensitively dependent on the cooling rate. Irrespective of the presence of Mo, slow furnace cooling at 4 K min-1 resulted in mainly pearlitic structures with some ferrite and coarse bainite, whereas fast cooling at 40 K min-1 produced martensite and some retained austenite, very fine pearlite, bainite, and some ferrite. Young's modulus, determined by tensile and ultrasonic tests, was in the range 110–155 GPa. Sintering with -60°C dewpoint resulted in tensile and transverse rupture strengths of 420 and 860 MPa for the Mn steel, rising to 530 and1130 MPa as a result of the Mo addition. This contrasts with strength decreases observed when processing included use of high oxygen containing ferromanganese and sintering with -35°C dewpoint.