Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis A Qualitative Machine Health Assessment by Running Quality Index(Izmir Institute of Technology, 2008) Önder, Olcay; Güden, MustafaMechanical components have limited life which is strongly related to the usage rate and operational conditions. Two parts could appear similar but actually not have the similar performances, because they had different usage rate, age, applied force and etc. during their life cycles. In this thesis, a new method that help to define the failure risk of mechanical components after customer utilization. The coding of Running Quality Index was performed in MATLAB program. The developed index summarizes all performance history of mechanical component/or part into a single number. A shaft test rig was designed to simulate force and number of cycle effects on the quality index. Tensile tests were conducted on St-37 steel samples exposed to varying forces, number of cycles and heat treatment to calculate Running Quality Index. The experimental results showed that increasing total number of cycles or repeated forces decreased the remaining life of samples. The developed quality index resulted in more risk penalty points for increasing number of cycles and repeated forces.Master Thesis Quasi-Static Crushing Behavior of Nomex Honeycomb Filled Thin-Walled Aluminum Tubes(Izmir Institute of Technology, 2008) Çakıroğlu, Cem; Güden, MustafaThe experimental and numerical studies presented in this thesis were focused on the experimental and numerical quasi-static crushing behavior of Nomexl1 honeycomb filled thin-walled aluminum tubes. Nomexl1 honeycombs having different cell sizes (3.2, 4.8 and 6.4 mm) and the same density (48 kg/m3) were used to fill thin walled aluminum tube, 25 mm in diameter and 0.29 mm in thickness. Compression tests were conducted at quasi-static the strain rates of 1.64 10-2, 6.56 10-3 and 3.28 10-3 s-1. The results showed that the honeycomb cell size had a strong effect on the crushing behavior. Decreasing cell size increased crushing loads and the specific absorbed energy values of empty tubes. The highest strengthening effect of filling was found in 3.2 mm cell size honeycomb filled tubes. Although no effects of 4.8 and 6.4 mm cellsize honeycomb filling on the deformation mode of tube was observed (mixed), 3.2 mm cell size honeycomb filling changed the deformation mode to mixed/concertina. The numerical model of empty tube, 6.4 mm cell size honeycomb and 6.4 mm cell size honeycomb filled tube were performed using LS-DYNATM and ANSYSTM finite element analysis programs. To acquire maximum computational efficiency, a mesh optimization was done. The effect of the honeycomb cell wall thickness was also investigated numerically and shown to have a strong effect on the crushing behavior of honeycomb. The experimental and numerical studies conducted showed that 3.2 mm cell size Nomex® honeycomb might become an alternative to aluminum foam filler in thin walled tubes as long as the tube crushing load was comparable with honeycomb crushing load.Master Thesis Preparation of Al-Ti Closed-Cell Metal Foams Via Foaming of Powder Compacts(Izmir Institute of Technology, 2008) Karsu, Nurettin Deniz; Güden, MustafaThe 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 Designing and Processing of Porous Ti6a14v Cages for Spinal Surgery(Izmir Institute of Technology, 2007) Hızal, Alpay; Güden, MustafaTi6Al6V foam materials were prepared with spherical particles in range of 20 90mm. Average porosity under various compaction pressure (200 MPa, 400 MPa, 500MPa, 600MPa, 700MPa), sintering temperature (1000oC-1400oC) and time (4h-6h) was observed in the range of 52%-72%. It was observed that sintered Ti6Al4V foam material can be potentially used for the spinal surgery. Furthermore, strength of the Ti6Al4V foam material in the porosity level of 40% is comparable with the human cortical bone. And also 22 Design of Experiment methods were used to investigate the major affective parameters during the processing of Ti6Al4V spinal cages. According to this investigation, sintering temperature, particle diameter and compaction pressure are the most affective parameters control the over all process of foam production. In the design process, protection case also designed for the foam material to put them inside of it. The reason of producing protection case is that eliminating the particle loosing from the sharp edges of the Ti6Al4V foam material.Master Thesis Preparation and Characterization of Sintered Ti-6a1 Powder Compacts(Izmir Institute of Technology, 2004) Çelik, Emrah; Güden, MustafaSintered Ti6Al4V powder compacts were prepared using atomized spherical and angular powders in the porosity range of 29-63%. Cylindrical green powder compacts cold compacted at various compaction pressures and then sintered at 1200 C for 2 h. The final porosities and average pore sizes were determined as functions of the applied compaction pressure and powder type. The compression deformation behavior of Ti6Al4V powder compacts was also investigated at quasi-static (1.6x10-3-1.6x10-1s-1) and high strain rate (300 and 900 s-1) conditions using conventional mechanical testing and Split Hopkinson Pressure Bar techniques, respectively. The mean pore size of the compacts varied between 29 and 171 Um depending on the particle size range of the powders used and the compaction pressure applied. Microscopic studies of as-received powders and sintered powder compacts showed that sintering at high temperature (1200oC) and subsequent relatively slow-rate cooling in the furnace transformed the microstructure of spherical powder from the acicular alpha to the Widmanstatten microstructure and angular powder from bimodal to equiaxed+ Widmanstatten microstructure.In compression testing, at both quasi-static and high strain rate conditions, the compacts failed primarily by shear band formation along the diagonal axis 45 C to the loading direction. Increasing strain rate was found to increase both the flow stress and the compressive strength of spherical powder compacts while it did not affect the critical strain for shear localization. The mechanical properties of angular powder compacts were further shown to be a function of powder size; larger the particle size higher the percentage of equiaxed structure while in compacts of particles <100 um relatively large voids resulted in reduced strength and ductility. Microscopic analyses of deformed but not failed and failed spherical powder compact 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/beta interface and macrocraking by void coalescence in the interparticle bond region. In angular powder compacts, the failure was granular brittle type at the interparticle bond region while the compact samples of particles <100 um fractured transgranularly through the voids. The strength of the sintered compacts 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 compacts suitable for cortical bone replacement.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 Quasi-Static Axial Compression Behavior of Empty and Polystyrene Foam Filled Aluminum Tubes(Izmir Institute of Technology, 2003) Toksoy, Ahmet Kaan; Güden, MustafaThe strengthening effect of foam filling and the effect of foam filling on the crushing properties of the light weight foam filled circular tubes were investigated through the polystyrene foam filled thin-walled Al tubes of 16 and 25 mm in diameter. The empty tubes crushed progressively in asymmetric (diamond) mode. The foam filling however turned the deformation mode into progressive axisymmetric (concertina) mode in 25 mm Al tube, while the deformation mode in foam filled 16 mm Al tube remained to be the same with that of the empty tube. The strengthening coefficients of foam-filling defined as the ratio between the increase in the average crushing load of the filled tube with respect to empty tube and plateau load (load corresponding to the plateau stress of the foam) were found to be 1.8 and 3.2 for the concertina and diamond mode of deformation, respectively. The higher value of strengthening in diamond mode of deformation was attributed to the filler deformation beyond the densification region. This was also confirmed by the microscopic observation of the partially crushed sections of the filled tubes. The interaction effect between tube and filler was assessed by the compression testing of the partially foam filled tubes. The effects of filler density, deformation rate (in the range between 0.001-0.04 s-1) and the use of adhesive between the tube wall and filler on the average crushing load, stroke efficiency and specific absorbed energy of the tubes were determined. The specific absorbed energy of the filled tube was compared with that of the empty tubes of wall thickening on the equal mass basis. Finally, two modes of deformation modes were proposed for the crushing behavior of the foam filled thin-walled Al tubes.Master Thesis Modeling Dynamic Behavior of Metal Matrix Composites(Izmir Institute of Technology, 2002) Tirtom, İsmail; Güden, MustafaA numerical investigation has been conducted on the strain rate dependent compression mechanical behavior of a SiC-particulate reinforced Al (2024-O) metal matrix composite. The effect of particle volume fraction on the strain rate sensitivity of the composite was determined using axisymmetric Finite Element unit cell models, where the particles are treated as elastic spheres embedded within a visco-plastic matrix, implemented in LUSAS Finite Element Analysis program. Particles are taken to be elastic, equal-sized, spherical and uniformly distributed in the matrix. The strain rate dependent constitutive behavior of the matrix material uses a linear relation between stress and strain rate formulation and is obtained from independent experimental results on the matrix. The flow stress of the composites is predicted over a range of strain rates for different particle volume fractions. Numerical results of the flow stress and strain rate sensitivity of the composite were also compared with those of experimental results, for 15% SiC particle reinforced 2024-O Al metal matrix composite. Influence of particle shape on the behavior of the MMC at high strain rates is also investigated. A unit cell, which is an elastic cylinder embedded within a visco-plastic matrix, is used. It is also shown that the rate dependent flow stress and local stress in the microstructure are influenced by particle shape. If reinforcement edge sharpness increases, local stress increases at that area. The results show that both the flow stress and the strain rate sensitivity increase with increasing volume fraction of the reinforcement due to the constraining effect of the reinforcement. Numerical calculations have shown an increased strain rate sensitivity of the composite over the matrix alloy. The discrepancy found between numerical and experimental results was finally discussed based on geometrical and microstructural parameters that might affect the composite flow stress and strain rate sensitivity.Master Thesis Quasi-Static and High Strain-Rate Mechanical Behavior of Fp™ (α-Alumina) Long Fiber Reinforced Magnesium and Aluminum Metal Matrix Composites(Izmir Institute of Technology, 2004) Akil, Övünç; Güden, MustafaThe mechanical response of an FP long fiber (35%) Mg composite has been determined in the transverse and longitudinal directions in compression. Results were also compared with those of a similar composite of Al matrix. It was found that the composite in the transverse direction exhibited strain rate sensitivity of the flow stress and maximum stress within the studied strain rate range (10-4 to 1x103s-1). However the increase in strain rate decreased the failure strain. Microscopic observations on the failed samples have shown that the composite failed predominantly by shear banding. Near to the fracture surface DRX grains were observed within the shear band and it was proposedthat the lower ductility of the composite at increasing strain rates was due to the early DRX grain formation which softened thecomposite and resulted in lower ductility. Although twinning was observed in the deformed cross-sections of the samples at all strain rates particularly near the shear band region, it was proposed that the main deformation mechanism was slip which was evidenced by the slip lines on the fracture surface. The strain rate sensitivity in fracture stress of the composite in transverse direction was also found to be similar to that of the Al composite tested in the same direction. In the longitudinal direction, the composite failed by kink formation at quasi-static strain rates, while kinking and splitting at high strain rates. The maximum stress in the axial direction was however foundto be strain rate insensitive. In this direction similar to transverse direction DRXgrain formation was observed in the kink region. The lack of strain rate sensitivity in this direction was attributed to DRX grain formation at high strain rates combined with adiabatic heating and the brittle nature of the composite leading to fluctuatitonin the compressive strength.