Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Conference Object High Strain Rate Reloading Compresson Testing of a Closed-Cell Alumnum Foam(The European Association for Experimental Mechanics, 2007) Taşdemirci, Alper; Güden, Mustafa; Hall, Ian W.Aluminum (Al) closed-cell foams are materials of increasing importance because they have good energy absorption capabilities combined with good thermal and acoustic properties. They can convert much of the impact energy into plastic energy and absorb more energy than bulk metals at relatively low stresses. When used as filling materials in tubes, they increase total energy absorption over the sum of the energy absorbed by foam alone and tube alone [1]. In designing with metallic foams as energy absorbing fillers, mechanical properties are needed for strain rates corresponding to those created by impact events. Quasi-static mechanical behavior of metallic foams has been fairly extensively studied, but data concerning high strain rate mechanical behavior of these materials are, however, rather sparse [2,3]. This study was initiated, therefore, to study and model the high strain rate mechanical behavior of an Al foam produced by foaming of powder compacts and to compare it with quasi-static behavior and, hence, determine any effect on energy absorbing capacity.Conference Object Sic-vıskır/alüminyum Kompozit Köpüklerin Hazırlanması ve Mekanik Özelliklerinin Belirlenmesi(Pamukkale Üniversitesi, 2004) Saatçi, Levent; Güden, MustafaKöpükleştirici TiH2 içeren SiC-viskır/Al kompozit tabletler erime sıcaklığının üzerinde ısıtılarak köpükleşme davranışları belirlenmiştir. SiC-vıskır katkısının köpükleşme ve mekanik özelliklere (basma) etkisini belirlemek üzere aynı sıcak-pesleme ve köpükleşme parametleri kullanılarak saf alüminyum tabletler hazırlanmıştır. Köpükleşme sıcaklığı sabit tutulup 750oC olarak seçilmiştir. Tabletlerin doğrusal büyümeleri farklı sürelerde fırında köpükleşen numunelerin boyutları ölçülerek bulunmuştur. Köpükler hazırlandıktan sonra mekanik özellikleri belirlenmek üzere, sabit hızda basma testi uygulanmıştır. Sonuçlar, SiCv/Al ve Al tabletlerde köpükleşmenin benzer olduğunu fakat SiC-vıskır katkısının plato gerilmesini önemli derecede artırdığını göstermiştir.Article Citation - WoS: 12Citation - Scopus: 12The Effect of Strain Rate on the Compressive Deformation Behavior of a Sintered Ti6al4v Powder Compact(Elsevier Ltd., 2008) Taşdemirci, Alper; Hızal, Alpay; Altındiş, Mustafa; Hall, Ian W.; Güden, MustafaThe high strain rate (220–550 s−1) and quasi-static (0.0016 s−1) compression deformation behavior of a sintered Ti6Al4V powder compact was investigated. The compact was prepared using atomized spherical particles (100–200 μm) and contained 38 ± 1% porosity. The deformation sequences of the tested samples were further recorded by high speed camera and analyzed as a function of strain. The failure of the compact, which was found to be similar in the studied high strain rate and quasi-static strain rate testing regimes, occurs through particle decohesion along the surface of the two cones in a ductile (dimpled) mode consisting of void initiation and growth and by void coalescence in the interparticle bond region. The effect of strain rate was to increase the flow stress and compressive strength of the compact while the critical strain corresponding to the maximum stress was shown to be strain rate independent.Article Citation - WoS: 24Citation - Scopus: 26Split Hopkinson Pressure Bar Compression Testing of an Aluminum Alloy: Effect of Lubricant Type(Chapman & Hall, 2003) Hall, Ian W.; Güden, MustafaThe Split Hopkinson Pressure Bar (SHPB), or Kolsky Bar, is widely used for studying the dynamic mechanical properties of metals and other materials. A cylindrical specimen is sandwiched between the incident and transmitter bars, Fig. 1, and a constant amplitude elastic wave is generated by the striker bar. Strain gages mounted on the incident and transmitter bars allow the compressive stress-strain response of the specimen to be established using uniaxial elastic wave theory [1]. A more detailed overview of SHPB testing is found in [2]. Lubricant is usually applied to the interfaces because the presence of any frictional effect on the specimen surfaces forms a multiaxial stress-state and invalidates one of the most important assumptions of the SHPB analysis, namely, a uniaxial stress state. This paper quantifies the effect for an aluminum alloy.Article Citation - WoS: 54Citation - Scopus: 62Sic-Particulate Aluminum Composite Foams Produced by Powder Compacts: Foaming and Compression Behavior(Springer Verlag, 2003) Elbir, Semih; Yılmaz, Selahattin; Toksoy, Ahmet Kaan; Güden, Mustafa; Hall, Ian W.The foaming behavior of SiC-particulate (8.6% by volume) aluminum composite powder compacts contained Titanium Hydride blowing agent was investigated by heating above the melting temperature (750°C) in a pre-heated furnace. Aluminum powder compacts were also prepared and foamed using similar compaction and foaming parameters in order to determine the effect of SiC-particulate addition on foaming and compression behavior. The linear expansions of the compacts at various furnace holding times were ex situ determined. Optical and scanning electron microscopy techniques were used to characterize prepared and deformed foams microstructures. The SiC-particulate addition was found to increase the linear expansion and reduce the extent of the liquid metal drainage and cell coarsening of the aluminum compacts. The composite foam samples also showed higher compressive stresses, but a more brittle behavior as compared with aluminum foams.Article Citation - WoS: 55Citation - Scopus: 61Sic-Particulate Aluminum Composite Foams Produced From Powder Compacts: Foaming and Compression Behavior(Springer Verlag, 2006) Güden, Mustafa; Yüksel, SinanThe foaming behavior of SiC-particulate (SiCp) aluminum composite powder compacts containing titanium hydride blowing agent was investigated by heating to 750°C in a pre-heated furnace. Aluminum powder compacts were also prepared and foamed using similar compaction and foaming parameters in order to determine the effect of SiCp-addition on the foaming and compression behavior. The SiCp-addition (10 wt%) was found to increase the linear expansion of the Al powder compacts presumably by increasing the surface as well as the bulk viscosities. The compression tests conducted on Al and 10 and 20% SiCp foams further showed a more brittle compression behavior of SiCp/Al foams as compared with Al foams. The collapse stresses of Al and 10% SiCp/Al foams were also predicted using the equations developed for the open and closed cell foams. Predictions have shown that Al foam samples behaved similar to open cell foams, while 10% SiCp/Al foam collapse stress values were found between those of open and closed cell foams, biasing towards those of the open cell foams.Article Citation - WoS: 11Citation - Scopus: 14Quasi-Static and Dynamic Compression Behaviour of an Fptm Alumina-Reinforced Aluminium Metal Matrix Composite(Springer Verlag, 1998) Güden, Mustafa; Hall, Ian W.An aluminium metal matrix composite reinforced with continuous unidirectional α-alumina fibres has been compression tested at quasi-static and dynamic strain rates. In the transverse direction, the composite showed increasing flow stress (at 5% strain) and maximum stress within the studied strain rates, 10−3−3 × 103 s−1. In the longitudinal direction, the maximum stress of the composite increased similarly with increasing strain rates within the range 10−5−7 × 102 s−1. It is shown that, if brooming of the sample ends can be suppressed, the failure stress of the composite in longitudinal compression increases significantly. Metallographic observations reveal the typical modes of damage initiation in the composite.Article Citation - WoS: 30Citation - Scopus: 33Processing and Compression Testing of Ti6al4v Foams for Biomedical Applications(Springer Verlag, 2009) Dizlek, Mustafa Eren; Güden, Mustafa; Türkan, Uğur; Taşdemirci, AlperOpen cell Ti6Al4V foams (60% porosity) were prepared at sintering temperatures between 1,200 and 1,350 °C using ammonium bicarbonate particles (315–500 μm) as space holder. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macropores (300–500 μm) and micropores (1–30 μm). Compression tests have shown that increasing sintering temperature increased the elastic modulus, yield and compressive strength, and failure strain of foams. The improvements in the mechanical properties of foams prepared using smaller size Ti64 powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. Finally, the strength of foams sintered at 1,350 °C was found to satisfy the strength requirement for cancellous bone replacement.Article Citation - WoS: 153Citation - Scopus: 163Predicting Energy Absorption in a Foam-Filled Thin-Walled Aluminum Tube Based on Experimentally Determined Strengthening Coefficient(Elsevier Ltd., 2006) Kavi, Halit; Toksoy, Ahmet Kaan; Güden, MustafaThe energy absorption in a foam-filled thin-walled circular Al tube was investigated based on the experimentally determined strengthening coefficient of filling using Al and polystyrene closed-cell foams with three different densities. Foam filling was found to change the deformation mode of tube from diamond (empty tube) into concertina, regardless the foam type and density used. 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 effective in increasing the specific energy than simply thickening the tube wall. It was shown that for efficient foam filling an appropriate foam-tube combination must be selected by taking into account the magnitude of strengthening coefficient of foam filling and the foam filler plateau load.Article Citation - WoS: 37High Strain-Rate Compression Testing of a Short-Fiber Reinforced Aluminum Composite(Elsevier Ltd., 1997) Güden, Mustafa; Hall, Ian W.Compression behavior of 15–26 Vf% Saffil™ short-fiber reinforced Al-1.17wt.%Cu alloy metal matrix composites has been determined over a strain-rate range of approximately 10−4 to 2×103 s−1. The strain-rate sensitivity of composite samples at 4% strain, tested parallel and normal to the plane of reinforcement, was found to be higher than that of unreinforced alloy in the strain-rate range studied. Quantitative analysis of fiber fragment lengths from samples tested to different strain levels showed that, at small strains, high strain-rate testing induced a relatively shorter fiber fragment length distribution in the composite compared to quasi-static testing. At quasi-static strain rates, the fiber strengthening effect was found to increase with increasing Vf% and was higher in samples tested parallel to the planar random array. The observed anisotropy of the composite at quasi-static strain rates was also observed to continue into the high strain-rate regime. Microscopic observations on composite samples tested quasi-statically and dynamically to a range of strains showed that the major damage process involved during compression testing was fiber breakage followed by the microcracking of the matrix at relatively large strains. Fiber breakage modes were found to be mostly shearing and buckling.