Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 23Citation - Scopus: 24Determination of the Material Model and Damage Parameters of a Carbon Fiber Reinforced Laminated Epoxy Composite for High Strain Rate Planar Compression(Elsevier Ltd., 2021) Shi, C.; Guo, B.; Sarıkaya, Mustafa; Çelik, Muhammet; Chen, P.; Güden, MustafaThe progressive failure of a 0°/90° laminated carbon fiber reinforced epoxy composite was modeled in LS-DYNA using the MAT_162 material model, including the strain rate, damage progression and anisotropy effects. In addition to conventional standard and non-standard tests, double-shear and Brazilian tests were applied to determine the through-thickness shear modulus and the through-thickness tensile strength of the composite, respectively. The modulus reduction and strain softening for shear and delamination parameters were calibrated by low velocity drop-weight impact tests. The rate sensitivities of the modulus and strength of in-plane and through-thickness direction were determined by the compression tests at quasi-static and high strain rates. The fidelity of the determined model parameters was finally verified in the in-plane and through-thickness direction by the 3D numerical models of the Split Hopkinson Pressure Bar compression tests. The numerical bar stresses and damage progressions modes showed acceptable correlations with those of the experiments in both directions. The composite failed both numerically and experimentally by the fiber buckling induced fiber-matrix axial splitting in the in-plane and the matrix shear fracture in the through-thickness direction. © 2020Article 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.Article Citation - WoS: 27Citation - Scopus: 28Split Hopkinson Pressure Bar Multiple Reloading and Modeling of a 316 L Stainless Steel Metallic Hollow Sphere Structure(Elsevier Ltd., 2010) Taşdemirci, Alper; Ergönenç, Çağrı; Güden, MustafaThe high strain rate (600 s−1) compression deformation of a 316 L metallic hollow sphere (MHS) structure (density: 500 kg m−3; average outer hollow sphere diameter: 2 mm and wall thickness: 45 μm) was determined both numerically and experimentally. The experimental compressive stress–strain behavior at high strain rates until about large strains was obtained with multiple reloading tests using a large-diameter compression type aluminum Split Hopkinson Pressure Bar (SHPB) test apparatus. The multiple reloading of MHS samples in SHPB was analyzed with a 3D finite element model using the commercial explicit finite element code LS-DYNA. The tested MHS samples showed increased crushing stress values, when the strain rate increased from quasi-static (0.8 × 10−4 s−1) to high strain rate (600 s−1). Experimentally and numerically deformed sections of MHS samples tested showed very similar crushing characteristics; plastic hinge formation, the indentation of the spheres at the contact regions and sphere wall buckling at intermediate strains. The extent of micro-inertial effects was further predicted with the strain rate insensitive cell wall material model and with the strain rate sensitive behavior of MHS structure similar to that of the cell wall material. Based on the predictions, the strain rate sensitivity of the studied 316 L MHS sample was attributed to the strain rate sensitivity of the cell wall material and the micro-inertia.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: 32Citation - Scopus: 37Modeling Quasi-Static and High Strain Rate Deformation and Failure Behavior of a (±45) Symmetric E-glass/Polyester Composite Under Compressive Loading(Elsevier Ltd., 2013) Kara, Ali; Taşdemirci, Alper; Güden, MustafaQuasi-static (1 × 10−3–1 × 10−2 s−1) and high strain rate (∼1000 s−1) compressive mechanical response and fracture/failure of a (±45) symmetric E-glass/polyester composite along three perpendicular directions were determined experimentally and numerically. A numerical model in LS-DYNA 971 using material model MAT_162 was developed to investigate the compression deformation and fracture of the composite at quasi-static and high strain rates. The compressive stress–strain behaviors of the composite along three directions were found strain rate sensitive. The modulus and maximum stress of the composite increased with increasing strain rate, while the strain rate sensitivity in in-plane direction was higher than that in through-thickness direction. The damage progression determined by high speed camera in the specimens well agreed with that of numerical model. The numerical model successfully predicted the damage initiation and progression as well as the failure modes of the composite.Article Citation - WoS: 22Citation - Scopus: 28Mechanical Interlocking Between Porous Electrospun Polystyrene Fibers and an Epoxy Matrix(American Chemical Society, 2014) Demir, Mustafa Muammer; Horzum, Nesrin; Taşdemirci, Alper; Turan, Ali Kıvanç; Güden, MustafaAn epoxy matrix filled with nonwoven mats of porous polystyrene (PS) fibers processed by an electrospinning was compression tested at quasi-static (1 × 10–3 s–1) and high strain (315 s–1) rates. The electrospun PS fibers with a diameter between 6 and 9 μm, accommodated spherical pores on the surface with the sizes ranging from 0.1 to 0.2 μm. The filling epoxy matrix with 0.2 wt % PS fibers increased the compressive elastic modulus and compressive strength over those of neat epoxy resin. The microscopic observations indicated that the surface pores facilitated the resin intrusions into the fiber, enhancing the interlocking between resin and fibers, and increased the deformation energy expenditure of the polymer matrix.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.