Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Investigation of Compression Mechanical Behaviour of Aluminum Foam Filled Metal Tubes(Izmir Institute of Technology, 2004) Kavi, Halit; Güden, MustafaNovel crash element designs, composing of packing of foam-filled multi tubes, were investigated through compression testing at quasi-static deformation rates. Multi-tube designs involved the hexagonal and cubic packing of Al foam-filled deep drawn Al tubes inside rigid cylindrical and rectangular dies. For comparison purposes, empty Al tubes, Al and polystyrene foam-filled single tubes, Al and polystyrene foam-filled bitubular tubes and empty multi-tube designs of hexagonal and cubic packing were also tested under the similar test conditions. The Al-closed cell foams used for the filling of tubes were prepared in house using a patented foaming process. For each tube geometry investigated the average crushing load and specific energy absorption was calculated and the results were compared.It was shown that although foam filling resulted in higher energy absorption than the sum of the energy absorptions of the tube alone and foam alone, it was not more effective in increasing the specific energy than simply thickening the tube walls. The lower specific energy absorptions of the Al-foam filled single tubes based on the equal mass criterion were due to the relatively lower plateau stresses of the filler material used. The experimental results have further shown that both multi-tube and bitubular geometries exhibited higher specific energy absorption capabilities than those of foam-filled single tubes. The increased strengthening coefficients of the multi-tube geometries with foam filling were solely due to the frictional loads between the adjacent tube walls, tube walls and die wall and constraint effect of die itself. The frictional loads were also found to increase the specific energy absorption of empty multi-tube geometries. The effect of Al foam density was found to increase the specific energy absorption in multi-tube geometries.Master Thesis Preparation and Characterization of Aluminum Composite Closed-Cell Foams(Izmir Institute of Technology, 2001) Elbir, Semih; Güden, MustafaAn experimental study has been conducted to investigate the feasibility of the production of SiC-particulate (SiCp) reinforced Al (Aluminum) closed-cell foams using the foaming from powder compacts process and to determine the effect of SiCp addition on the foaming behavior of Al compacts and the mechanical properties of Al foams.The foaming behavior of SiCp/Al composite powder compacts and the compression mechanical behavior of SiCp/Al composite foams were determined and compared with those of pure Al compacts and Al foams prepared by the same processing parameters.Composite and Al powder compacts were prepared by hot uniaxial compaction inside a steel die at 425 oC for 1/2 hour under a constant die pressure of 220 MPa.Compacts of 99 % dense with a small amount of blowing agent of TiH2 (0.5 wt%) were heated above the melting temperature of Al inside a pre-heated furnace. During heating, as the TiH2 decomposed and released hydrogen, the compact expanded uniaxially. Foamed/partially foamed samples were taken from the furnace at the specified furnace holding times and their heights were measured in order to calculate linear expansion.Initial foaming experiments with Al compacts at 750 and 850 oC have shown that foaming at the former temperature was slower and more controllable, although linear expansion was similar at both temperatures. From these experiments, it was also found that rapid cooling of the liquid metal was necessary in order to maintain the liquid foam structure in the solid state.Foaming experiments of SiCp/Al and Al compacts at 750 oC have shown that SiCp addition a) increased linear expansion of the powder compacts and b) reduced the extent of liquid metal drainage. SiCp addition also increased the plateau stress and energy absorption capability of the Al foams. These results have shown the potential of composite foams for tailoring energy absorption of Al foams for varying levels of impact stresses.Foaming experiments have also been conducted on aluminum oxideparticulate/Al and SiC-whisker/Al composites compacts prepared using the same compaction parameters and foamed at the same temperature, 750 oC.Master Thesis Designing and Manufacturing of Porous Spinal Cages Using Ti6a14v Foamed Metal(Izmir Institute of Technology, 2009) Dizlek, Mustafa Eren; Güden, MustafaOpen cell Ti6Al4V foams with varying porosities (50, 60 and 70%) were prepared at sintering temperatures between 1200 and 1350 °C using ammonium bicarbonate particles (315 - 500 .m) as space holder. Two different biomedical grade commercial, gas atomized spherical Ti6Al4V powders were used to prepare foams. Powder 1 was in size range of between 45 - 150 .m and Powder 2 in size range of between 30 - 90 .m. The foams were sintered under argon atmosphere in a tightly enclosed tube furnace. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macro pores (300 - 500 .m) and micro pores (1 - 30 .m). Compression tests of foam samples have shown that increasing sintering temperature or decreasing porosity increased the elastic modulus, yield and compressive strength and failure strain. The improvement in the mechanical properties of foams prepared using smaller size Ti6Al4V powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. The foam prepared with optimum porosity, pore size and mechanical properties for bone in-growth was further used to produce prototype porous spinal cages which are widely used in spinal surgery for vertebrae fixation. The geometries and size of the prototype spinal cages were determined through the measurements taken from human vertebrae. The foams for spinal cage preparation were first prepared in the form of plates and then core-drilled using water jet based on the design geometrical parameters determined for each vertebra segment.Master Thesis Processing and Mechanical Testing of Ti6a14v Foams for Hard Tissue Implant Applications(Izmir Institute of Technology, 2005) Akar, Egemen; Güden, MustafaSintered Ti6Al4V alloy powder foams were prepared using atomized spherical powders in the porosity range of 52-72 %. For increasing porosity range, space holder was used. Spherical powder foams were cold compacted at (200, 300, 400, 500 MPa) compaction pressures and then sintered at 1200 °C for 2 h and 1300 °C for 2-4-6 h. The final porosities and average pore sizes were determined as functions of the applied compaction pressure and sintered time.The mean pore size of the foams varied between 94 and 148 mm depending on the particle size range of the powders used and the compaction pressure applied.Microscopic studies of sintered powder foams showed that sintering at high temperature (1200°C and 1300°C) and subsequent relatively slow-rate cooling in the furnace transformed the microstructure of spherical powder from the acicular alpha to the Widmansttten microstructure.In compression testing, at quasi-static, the foams failed primarily by shear band formation along the diagonal axis 45 to the loading direction. Microscopic analyses of deformed but not failed and failed spherical powder foam samples further showed that fracture occurred in a ductile (dimpled) mode consisting of void initiation and growth in alpha phase and/or at the alpha/b interface and macrocraking by void coalescence in the interparticle bond region.The strength of the sintered foams was further shown to satisfy the strength requirements for cancellous bone replacement. The strength of the compacts having porosity level of 40% and/or lower was comparable with that of human cortical bone.Compared to Ti powder compacts of previous studies, Ti6Al4V powder compacts provided higher strength and increased porosity level of the foams suitable for cortical bone replacement.Master Thesis Inertial Effect in Aluminum Metal Foams(Izmir Institute of Technology, 2011) Kocatürk, Onur; Güden, MustafaIn this study, Al tubes, Al foams of different types, Al sandwich plates of various configurations (orientations) and brittle glass foam samples were quasistatically reloaded in order to assess any micro inertia effect on the deformation stresses. Al foams tested quasi-statically were further reloaded (interrupted test) in Split Hopkinson Bar (SHPB) at dynamic strain rates in order to see effect of strain rate on micro inertia effect. Al empty tubes experienced micro inertia independent (Type I) deformation behavior in lateral compression and micro inertia dependent (Type II) deformation behavior in axial compression. The lack of strain rate sensitivity of the tested Alulight (AlSi10) closed cell Al foams (Al/Si) produced through powder route within the studied strain rate regime was attributed to the foam cell wall fracture during cell wall buckling. While Al foams with and without SiC addition showed micro inertia effect through progressive cell wall bending. In accord with these observations, Al and Al/SiC foams showed the strain rate sensitive, while Alulight foams showed strain rate insensitive plateau stress in the SHPB compression tests. The layer configuration/orientation was shown to affect Al sandwich plate deformation. Progressive bending of the interlayer fins resulted in strain rate depending crushing stress, while shearing of the interlayer resulted in strain rate insensitive deformation stress. As was expected, the strength enhancement was not seen in glass foam specimens tested as the cell walls were fractured under compressive loads. Finally, a simple testing method was shown to investigate micro inertia effect in hollow and cellular Al structures.