Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
Browse
32 results
Search Results
Conference Object Citation - WoS: 1Citation - Scopus: 1Numerical and Experimental Studies of High Strain Rate Mechanical Behavior of E-glass/Polyester Composite Laminates(The American Society of Mechanical Engineers(ASME), 2010) Tunusoğlu, Gözde; Taşdemirci, Alper; Güden, Mustafa; Hall, Ian W.Quasi-static ∼10-3 s-1) and high strain rate (∼850 s-1) compression behavior of an E-glass/polyester composite was determined in the through-thickness and in-plane directions. In both directions, modulus and failure strength increased with increasing strain rate. Higher strain rate sensitivity for both elastic modulus and failure strength was observed in the in-plane direction. A numerical model was developed to investigate the compressive deformation and fracture of an E-glass/polyester composite. Excellent agreement was demonstrated for the case of high strain rate loading. Also, the fracture geometries were successfully predicted with the numerical model.Conference Object Off-Axis Properties of Cross-Ply Metal Matrix Composites at Quasi-Static and High Strain Rates(Elsevier Ltd., 2011) Hall, Ian W.; Taşdemirci, Alper; Kara, AliCylindrical samples of a 0/90° cross-ply Nextel 610™/A1-6061 (∼55Vf%) metal matrix composite have been subjected to compression testing at quasi-static and high strain rates over a range of angles between 0° and ±45° with respect to the principal fiber directions. The results, combined with testing in the longitudinal, transverse and through thickness directions, provide a detailed description of the response of such composites over a wide range of orientations. In addition, metallographic and fractographic studies along with high-speed camera records provide detailed information about the sequence of deformation events leading to fracture. Results confirm not only the strong dependence of mechanical properties upon orientation but also the critical importance of precise fiber alignment and processing in obtaining the desired theoretical properties. A misalignment of 10° was sufficient to cause an -40% decrease in maximum stress and the properties were found to vary by >70% over the orientations investigated. The high strain rate properties were generally significantly greater than those measured quasi-statically. A numerical model based on the commercial explicit finite element code LS-DYNA was used to investigate the compressive deformation and fracture of the composite. Experimental results are compared with those of the numerical model. © 2011 Published by Elsevier Ltd.Article Citation - WoS: 9Citation - Scopus: 9Quasi-Static and High Strain Rate Properties of a Cross-Ply Metal Matrix Composite(Elsevier Ltd., 2009) Hall, Ian W.; Taşdemirci, Alper; Derrick, J.A series of compression tests has been carried out at quasi-static and high strain rates on cylindrical samples of an alumina fiber/Al-6061 metal matrix composite. The composite plates were prepared with fibers in the 0°, 0/90° and ±45° orientations. It was found that the mechanical properties were strongly dependent upon the imposed strain rate, with fracture stress increases of >50% being noted for several orientations at high strain rates: these increases are not believed to be related to strain rate sensitivity of either the matrix or fibers but to arise from the inertia of fragments which remain in place after fracture and continue to bear load. Also, and in contradiction to behavior anticipated from the rule of mixtures, it was found that 0/90° samples exhibited properties superior to those of 0° unidirectional samples. High-speed photography was used to confirm the sequence of deformation and fracture events at high strain rate. © 2008 Elsevier B.V. All rights reserved.Article Citation - WoS: 33Citation - Scopus: 41Development of Novel Multilayer Materials for Impact Applications: a Combined Numerical and Experimental Approach(Elsevier Ltd., 2009) Taşdemirci, Alper; Hall, Ian W.A well-verified and validated numerical model was used to investigate stress wave propagation in a multilayer material subjected to impact loading. The baseline material consisted of a ceramic faceplate and composite backing plate separated by a rubber or teflon foam interlayer: several variants were investigated in which the number, type, and total thicknesses of the interlayers were altered. Comparison of the variants showed that the use of multiple teflon foam interlayers could drastically reduce the average stress in the multilayer material. Based on the numerical results, further experimental work was undertaken upon one of the variants. Very large and unexpected tensile stress oscillations were observed in the ceramic layers, leading to a refinement of the numerical model which successfully reproduced the oscillations and also demonstrated that separation of the sample layers led to trapping of the stress wave within the layers. Use of the validated numerical model allowed detailed analysis of the processes of wave transmission and demonstrates the important synergy that can exist between experimental and modeling studies. The current study provides a valuable starting point for designing future multilayer materials with specific, controlled properties.Article Citation - WoS: 17Citation - Scopus: 20Numerical and Experimental Studies of Damage Generation in a Polymer Composite Material at High Strain Rates(Elsevier Ltd., 2006) Taşdemirci, Alper; Hall, Ian W.Samples of S2-glass/epoxy composites have been subjected to microstructural investigation after testing in compression at quasi-static and high strain rates using the split Hopkinson pressure bar. A numerical model was developed that accurately describes the high strain rate mechanical response of the samples. Moreover, in contrast with earlier phenomenological or constitutive models, the model can also predict a variety of failure modes such as delamination, matrix cracking or fiber crushing. High-speed photography was used to check the model results. Interrupted tests, followed by metallographic examination, have revealed that the sequence of damage events differs between quasi-static and high strain rate regimes. The effect of sample size on measured mechanical properties is noted and is confirmed via numerical modeling.Article Citation - WoS: 29Citation - Scopus: 38The Effects of Plastic Deformation on Stress Wave Propagation in Multi-Layer Materials(Elsevier Ltd., 2007) Taşdemirci, Alper; Hall, Ian W.The behavior of a multi-layer material at high strain rate and the effect of plastic deformation on stress wave propagation were investigated by a combination of experimental and numerical techniques. Plastic deformation effects were studied in multi-layer materials consisting of ceramic, copper and aluminum subjected to large strains under high strain rate loading. First, stress wave propagation behavior for the monolithic metals was studied, and then extended to multilayer combinations of these metals with each other and with a ceramic layer. The axial stress distributions were found to be non-uniform in the elastic deformation range of the specimen. The degree of non-uniformity was much more pronounced in the multi-layer samples consisting of different materials. The presence of a ceramic layer increased the magnitudes of stress gradients at the interfaces. It was also found that a major effect of plastic deformation is a tendency to produce a more homogeneous stress distribution within the components. The implications of these observations for practical systems are discussed.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 Axial Compression of Aluminum Closed-Cell Foam Filled and Empty Aluminum Tubes(Uludağ Üniversitesi, 2002) Toksoy, Ahmet Kaan; Güden, Mustafa; Hall, Ian W.Aluminum closed-cell foam filled aluminum tubes with a polyester bonding layer between foam core and tube wall have been compression tested in ord er to detemiine specific energy absorption for the crash box applications. Aluminum foam, empty and foam filled tubes without bonding layer were also tested for comparison purposes, Preliminary results have shown that interaction effect has been found in foam filled tubes with polyester layer. In order to identify deforiDation mechanisms involving with tube deforination, deformed empty and foam filled tubes crosssections were microscopically analyzed and operative defoimationmechanisms were determined.Conference Object Alüminyum Oksit Uzun Fiber Destekli Mg Matris Kompozitlerin Statik ve Yüksek Hız Basma Davranışı(Pamukkale Üniversitesi, 2004) Akil, Övünç; Güden, Mustafa; Çiftçioğlu, Muhsin; Hall, Ian W.; Taşdemirci, AlperBu çalışmada uzun alüminyum oksit (FP™) fiber destekli magnezyum matris kompozitlerin enine basma davranışının deformasyon hızına bağlı değişimi araştırılmıştır. Silindirik numuneler fiber doğrultusuna dik yönde değişik uzama oranlarında Split Hopkinson basınç çubuğu ve statik mekanik test cihazı kullanılarak test edilmiş uzama-gerilme ilişkileri incelenmiştir. Bunun yanında optik mikroskop ve SEM kullanılarak kırılma mekaniği belirlenmeye çalışılmıştır. Çalışma sonucunda malzemenin enine basma mukavemetinin deformasyon hızı ile arttığı tespit edilmiş olup mikro-yapı incelemesinde deformasyonun ikizlenme ve kayma ile gerçekleştiği belirlenmiştir.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.