Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 13Citation - Scopus: 14The Quasi-Static Crush Response of Electron-Beam Ti6al4v Body-Centred Lattices: The Effect of the Number of Cells, Strut Diameter and Face Sheet(Wiley, 2022) Güden, Mustafa; Alpkaya, Alican Tuncay; Arslan Hamat, Burcu; Hızlı, Burak; Taşdemirci, Alper; Tanrıkulu, A. Alptuğ; Yavaş, HakanThe effect of the number of cells, strut diameter and face sheet on the compression of electron-beam-melt (EBM) Ti6Al4V (Ti64) body-centred-cubic (BCC) lattices was investigated experimentally and numerically. The lattices with the same relative density (~0.182) were fabricated with and without 2-mm-thick face sheets in 10 and 5 mm cell size, 8–125 unit cell (two to five cells/edge) and 2 and 1 mm strut diameter. The experimental compression tests were further numerically simulated in the LS-DYNA. Experimentally two bending-dominated crushing modes, namely, lateral and diagonal layer crushing, were determined. The numerical models however exhibited merely a bending-dominated lateral layer crushing mode when the erosion strain was 0.4 and without face-sheet models showed a diagonal layer crushing mode when the erosion strain was 0.3. Lower erosion strains promoted a diagonal layer crushing mode by introducing geometrical inhomogeneity to the lattice, leading to strain localisation as similar to the face sheets which introduced extensive strut bending in the layers adjacent to the face sheets. The face-sheet model showed a higher but decreasing collapse strength at an increasing number of cells, just as opposite to the without face-sheet model, and the collapse strength of both models converged when the number of cells was higher than five-cell/edge. The decrease/increase of the collapse strengths of lattices before the critical number of cells was claimed mainly due to the size-imposed lattice boundary condition, rather than the specimen volume. The difference in the experimental collapse strengths between the 5- and the 10-mm cell-size lattices was ascribed to the variations in the microstructures—hence the material model parameters between the small-diameter and the large-diameter EBM-Ti64 strut lattices.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: 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: 19Citation - Scopus: 21Effect of Strain Rate on the Compressive Mechanical Behavior of a Continuous Alumina Fiber Reinforced Ze41a Magnesium Alloy Based Composite(Elsevier Ltd., 2006) Güden, Mustafa; Akil, Övünç; Taşdemirci, Alper; Çiftçioğlu, Muhsin; Hall, Ian W.The compressive mechanical response of an FP™ continuous fiber (35 vol.%) Mg composite has been determined in the transverse and longitudinal directions at quasi-static and high strain rates. 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 of 1.3 × 10−4 to 1550 s−1. The failure strain in this direction, however, decreased with increasing strain rate. Microscopic observations on the failed samples have shown that the composite failed by shear banding along the diagonal axis, 45° to the loading axis. Twinning was observed in the deformed cross-sections of the samples particularly in and near the shear band region. The strain rate sensitivity of the fracture stress of the composite in transverse direction is attributed to the matrix strain rate sensitivity. In the longitudinal direction, the composite failed by kink formation at quasi-static strain rates, while kinking and splitting were observed at the high strain rates. The maximum stress in the longitudinal direction was, however, found to be strain rate insensitive within the strain rate regime of 1.3 × 10−4 to 500 s−1. In this direction, similar to transverse direction, twinning was observed in the highly deformed kink region. Several different reasons are proposed for the strain rate insensitive compressive strength in this direction.Article Citation - WoS: 24Citation - Scopus: 26Diatom Frustule-Filled Epoxy: Experimental and Numerical Study of the Quasi-Static and High Strain Rate Compression Behavior(Elsevier Ltd., 2008) Taşdemirci, Alper; Yüksel, Sinan; Karsu, Deniz; Gültürk, Elif; Hall, Ian W.; Güden, MustafaIn this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress–time response and deformation sequence of the samples in high strain rate testing.Article Citation - WoS: 70Citation - Scopus: 81Experimental and Numerical Studies on the Quasi-Static and Dynamic Crushing Responses of Multi-Layer Trapezoidal Aluminum Corrugated Sandwiches(Elsevier Ltd., 2014) Kılıçaslan, Cenk; Güden, Mustafa; Kutlay Odacı, İsmet; Taşdemirci, AlperThe axial crushing responses of bonded and brazed multi-layer 1050 H14 trapezoid alaluminum corru- gated core (fin) sandwich structures, with and without aluminum interlayer sheets in 0°/0° and 0°/90° core orientations, were both experimentally and numerically investigated at quasi-static and dynamic strain rates. Multi-layering the core layers decreased the buckling stress and increased the densification strain. The experimental and simulation compression stress–strain curves showed reasonable agree-ments with each other. Two main crushing modes were observed experimentally and numerically: the progressive fin folding and the shearing interlayer aluminum sheets. Both, the simulation and experimental buckling and post-buckling stresses increased when the interlayer sheets were constraint laterally. The multi-layer samples without interlayer sheets in 0°/90° core orientation exhibited higher buckling stresses than the samples in 0°/0° core orientation. The increased buckling stress of 0°/0° oriented core samples without interlayer sheets at high strain rate was attributed to the micro-inertial effects which led to increased bending forces at higher impact velocities.