Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Güden, MustafaSubject: search.filters.subject.Metal foams

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Now showing 1 - 7 of 7
  • Master Thesis
    Preparation of Al-Ti Closed-Cell Metal Foams Via Foaming of Powder Compacts
    (Izmir Institute of Technology, 2008) Karsu, Nurettin Deniz; Güden, Mustafa
    The foaming behavior of 5 wt% 30-45, 45-56, 56-90, 90-106, 106-160 and 160-200 .m size spherical Ti6Al4V particle-added Al powder compacts were investigated for determining the effects of wetted particles on the expansion and stability of Al powder compacts. In order to determine the effect of particle-addition on the foaming behavior, Al compacts without particle addition prepared with same method were also foamed. Foaming experiments were performed using an in-situ foam expansion measuring system at 700-730C. Small compression test samples were further core drilled from Ti6Al4V-Al foam samples and tested at quasi-static strain rates.Al compacts showed the characteristic expansion-time curve, composing of 4 distinct regions. The expansion of 5 wt% Ti6Al4V-added compacts was found to be relatively low at small size particle additions, but increased with increasing particle size.Measurements of foam expansions of 30-45 .m size Ti6Al4V-added compacts with various weight percentages of particles showed that when the wt% of particles is lower than 2 wt%, the expansion behavior of the compacts became very similar to that of pure Al. Microscopic studies have further shown that Ti6Al4V addition reduced the drainage as compared with pure Al compacts. In foaming of Ti6Al4V-Al compacts, the liquid Al reacted with Ti6Al4V particles and formed TiAl3 particles. In relatively small size particle-added foams, TiAl3 particles dispersed through cell walls and cell edges, but at increased particle size, these particles were found next to the Ti6Al4V particles. The reduced drainage and lower foam expansions in the foaming of Ti6Al4V-added compacts were discussed based on the foam stabilization models in the literature. The reduced foamability of the compacts in small particle size Ti6Al4V addition was attributed to relatively high viscosities, due to higher cumulative surface area of the particles and higher rate of reaction between liquid Al and Ti6Al4V. The lower compression strength measured in Ti6Al4V-added foams was attributed to small specimen sizes, which could not show the mechanical properties of the bulk material.
  • Master Thesis
    Preparation and Characterization of Aluminum Composite Closed-Cell Foams
    (Izmir Institute of Technology, 2001) Elbir, Semih; Güden, Mustafa
    An 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
    Development of Lead Foams for Automobile Batteries
    (Izmir Institute of Technology, 2012) Savacı, Umut; Güden, Mustafa
    Open cell lead foam samples with, 48, 55, 60, 65 and 74% porosity, were successfully prepared by powder metallurgy and casting using ammonium bicarbonate, silica beads and salt particles as space holder filler. Additionally electrowinning and powder compact foaming methods were tried. The resulting foam samples resembled open foam cell structure; each cell had interconnections with neighboring cells. Small size lead (II) fluoride precipitates were observed interior of cells in the foam samples prepared using silica beads, resulting from the reaction between silica and HF acid during space holder removal. The compression stress-strain curve of foam samples prepared by powder metallurgy showed a brittle behavior following the initial elastic, while foam samples prepared by casting showed elastic-plastic characteristic metal foam deformation; crushing of cell edges on the bent cell walls and tearing of thin cell walls. The collapse stresses of the prepared foams were fitted with scaling relations. The imperfections such as curved, wrinkled and missing cell walls, voids on the cell edges and cell walls and non-uniform density lead to discrepancy between experimental and theoretical scaling parameters.
  • Master Thesis
    Crushing Behaviour of Aluminum Foam-Filled Composite Tubes
    (Izmir Institute of Technology, 2005) Yüksel, Sinan; Güden, Mustafa
    An experimental study has been conducted in order to determine the effect of Al-foam filling on the composite and hybrid (Al metal and composite) composite tubes.Tubes and fillers used in the experiments were prepared using the tube rolling and foaming from powder compacts methods, respectively. The composite was prepared using E-glass fiber fabric (2x2 twill fiber construction of 165 g/m2 areal density) and polyester matrix with a 45/45 fiber angle to the tube axis. The quasi-static crush tests were conducted axially on the empty, hybrid and foam filled tubes at 25 mm/min crosshead speed. The deformation sequences of the tubes were further recorded during the tests in order to identify the crushing modes of the tubes. Two failure mechanisms literally known as progressive crushing and catastrophic failure (compression shear) were observed during the crushing of empty composite tubes. The progressive crushing mode leaded to higher crushing loads hence Specific Absorbed Energies (SAE). The predominant progressive crushing mode of empty tubes of thinner wall section was attributed to the surface end defects introduced during sectioning of the tubes. In hybrid tubes, the deformation mode of Al tube was found to be a more complex form of the diamond mode of deformation, leading to higher SAE values than the sum of the SAEs of empty composite and empty metal tube. The increased load and SAE values ofhybrid tubes were attributed to the constraining effect of the composite to the metal tube folding. Results further showed that when the progressive crushing mode was taken into account hybrid tubes had lower SAE values than those of empty composite tubes. The foam filling of the composite tubes however showed two different results. It increased the foam filled tube crush loads over the sum of the crush loads of empty composite tube and foam. In the latter case it was not effective in increasing crush loads over the sum of the crush loads of empty composite tube and foam in the progressive crushing region. These two effects were discussed in terms of possible interactions between composite tube and foam.
  • Master Thesis
    Designing and Manufacturing of Porous Spinal Cages Using Ti6a14v Foamed Metal
    (Izmir Institute of Technology, 2009) Dizlek, Mustafa Eren; Güden, Mustafa
    Open 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, Mustafa
    Sintered 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, Mustafa
    In 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.