Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
Browse
7 results
Search Results
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: 25Citation - Scopus: 28High Strain Rate Deformation Behavior of a Continuous Fiber Reinforced Aluminum Metal Matrix Composite(Elsevier Ltd., 2000) Güden, Mustafa; Hall, Ian W.An aluminum metal matrix composite reinforced with continuous unidirectional α-Al2O3 fibers has been compression tested at quasi-static and dynamic strain rates. In the transverse direction, the composite showed increased flow stress and maximum stress within the studied strain rate regime, 10−3 to 3500 s−1. The strain rate sensitivity of the flow stress in this direction was found to be similar to that of a similar, but unreinforced, alloy determined from previous work. In the longitudinal direction, the maximum stress of the composite increased with increasing strain rate within the range 10−5 to 700 s−1. The strain rate dependent maximum stress in this direction was described by the strain rate dependent fiber buckling stress.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: 25Citation - Scopus: 36Effect of Strain Rate on the Compression Behaviour of a Woven Fabric S2-Glass Fiber Reinforced Vinyl Ester Composite(Elsevier, 2003) Akil, Övünç; Yıldırım, Uygar; Güden, Mustafa; Hall, Ian W.Quasi-static (~10−3s−1) and high strain rate (>500 s−1) compression behavior of an S2-glass woven fabric/vinyl ester composite plate was determined in the in-plane and through-thickness directions. In both directions, modulus and failure strength increased with increasing strain rate. A higher strain rate sensitive modulus was found in the through-thickness direction while a higher strain rate sensitive failure strength was found in the in-plane direction. In the in-plane direction, the failure mode was observed to change from splitting followed by “kink banding” (localized fiber buckling) to predominantly splitting at increasing strain rates, while it remained the same in the through-thickness direction.Article Citation - WoS: 26Citation - Scopus: 40Effect of Strain Rate on the Compression Behaviour of a Woven Glass Fiber/Sc-15 Composite(Elsevier Ltd., 2004) Güden, Mustafa; Yıldırım, Uygar; Hall, Ian W.Strain rate dependent compression behavior of a plain-weave S-2 glass fabric SC-15 epoxy (rubber toughened resin) composite plate, currently studied as the backing plate for composite armor applications, was determined in the through-thickness direction (normal to the fiber plane) in the strain rate regime of 1×10−4 to 1.1×103 s−1. In the studied strain rate regime, the modulus and failure strength of the composite were found to be rate sensitive and increased with increasing strain rate. Microscopic observations showed that the composite failed by ductile failure, involving matrix cracks and, later, cracking through and between the fiber layers. Crack deflections at rubber particle/matrix interface and particle pull-out were observed in the failed samples, contributing to the toughness of the composite.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.