Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Conference Object Citation - WoS: 6Citation - Scopus: 8The Effect of Spatial Interventions on Historic Buildings' Indoor Climate (case Study: Tire Necip Paşa Library, Izmir-Turkey)(Elsevier Ltd., 2017) Coşkun, Turgay; Gülhan, Özcan; Şahin, Cem Doğan; Durmuş Arsan, Zeynep; Gökçen Akkurt, GüldenThe indoor climate of historic libraries should meet rigorous requirements related to human thermal comfort and conservation of books, manuscripts and cultural proper-ties. Paper based collections in historic libraries can be deteriorated chemically, mechanically and biologically because of inadequate indoor climate conditions. In this paper, Necip Paşa Library, the historic library located in Tire-Izmir, Turkey, was selected as a case study. The chemical, mechanical and biological degradation risks on the manuscripts were evaluated based on the indoor climate parameters measured for one year period. The Library, consisting of a main hall, a manuscript zone and an entrance hall, was modelled via the dynamic simulation software, Design Builder. Calibration of the model was conducted with respect to the measured indoor temperature and relative humidity values. The portico/Revak at the south facade of Library was converted into the entrance hall by wooden framed windows in 1930. To be able to see the effect of that intervention on the indoor climate (correspondingly on degradation risk of the manuscripts), a new model, namely semi-open model, was created and simulated. A remarkable change has not been observed on chemical degradation risk when the results of semi-open and existing library models were compared, while mechanical and biological degradation risks were less in semi-open model.Conference Object Citation - WoS: 4Citation - Scopus: 4Investigation of Scholte and Stoneley Waves in Multi-Layered Systems(Elsevier Ltd., 2015) Önen, Onursal; Uz, Yusuf CanInterface waves are elastic waves that can propagate at the interface between two solids (Stoneley wave) or between a solid and a liquid (Scholte wave). In this study, properties of generalized Stoneley and Scholte waves are investigated analytically in a multi-layer system with both liquid-solid and solid-solid interfaces. The interface waves are modeled using partial waves in layers with finite thicknesses to trace quasi- and non-dispersive modes. Dispersion curves of the propagating modes and corresponding particle displacement profiles are obtained using numerical solution techniques with the global matrix method. Limiting conditions of quasi-modes are evaluated analytically for thickness and material selection. Furthermore, interference of the two interface waves and plate modes are investigated for small frequency-thickness products in the multi-interface system using dispersion curves and particle displacement profiles. Preliminary sensitivity analyses are also performed for development of multi sensing physical quantities such as temperature, viscosity and density simultaneously using interface waves.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: 2Citation - Scopus: 2Trait-based heterogeneous populations plus (TbHP+) genetic algorithm(Elsevier Ltd., 2009) Tayfur, Gökmen; Sevil, Hakkı Erhan; Gezgin, Erkin; Özdemir, SerhanThis study developed a variant of genetic algorithm (GA) model called the trait-based heterogeneous populations plus (TbHP+). The developed TbHP+ model employs a memory concept in the form of immunity and instinct to provide the populations with a more efficient guidance. Also, it has an ability to vary the number of individuals during the search process, thus allowing an automatic determination of the size of the population based on the individual qualities such as character fitness and credit for immunity. The algorithm was tested against the classical GA model in convergence and minimum error performance. For this purpose, 5 different mathematical functions from the literature were employed. The selected functions have different topological characteristics, ranging from simple convex curves with 2 variables to complex trigonometric ones having several hilly shapes with more than 2 variables. The developed model and the classical GA model were applied to finding the global minima of the functions. The comparison of the results revealed that the developed TbHP+ model outperformed the classical GA in faster convergence and minimum errors, which may be explained by the adaptive nature of the new paradigm.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.Conference Object Citation - WoS: 11Citation - Scopus: 18Experimental and Numerical Investigation of High Strain Rate Mechanical Behavior of a [0/45 - 45] Quadriaxial E-glass/Polyester Composite(Elsevier Ltd., 2011) Taşdemirci, Alper; Kara, Ali; Turan, Ali Kıvanç; Tunusoğlu, Gözde; Güden, Mustafa; Hall, Ian W.Quasi-static (10−3–10−1 s−1) and high strain rate (∼900 s−1) compression behavior of an E-Glass fiber woven fabric reinforced Polyester matrix composites was investigated by using a Shimadzu AG-I testing machine and a Split Hopkinson Pressure Bar apparatus in the Dynamic Testing and Modeling Laboratory of Izmir Institute of Technology. During the experiments, a high speed camera was used to determine deformation behavior. 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. Based upon these experimental data, a numerical model was developed using the commercial explicit finite element code LS-DYNA to investigate compressive deformation and damage behavior of composites. Excellent agreement was demonstrated for the case of high strain rate loading. Also, the fracture geometries were successfully predicted with the numerical model.