Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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2002 - 200912010 - 20151

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Author: search.filters.author.Güden, MustafaSubject: search.filters.subject.Finite element method

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  • Master Thesis
    Static and Dynamic Deformation Behavior of Combined Geometry Aisi 304l Stainless Stell Shells
    (Izmir Institute of Technology, 2015) Şahin, Selim; Taşdemirci, Alper; Güden, Mustafa
    In this study, the static and dynamic crushing behavior of combined geometry shells consisting of hemi-spherical and cylindrical segments were studied both experimentally and numerically. The proposed geometries were manufactured by deep drawing. Due to the nature of the deep drawing process, specimens inherited significant amount of residual stress/strain and thickness variation along the cross-section was observed. Thus, the manufacturing process was also numerically modeled explicitly. Quasi-static compression and dynamic drop weight tests were conducted both experimentally and numerically. The plastic deformation of the combined geometry shells started with the inward dimpling of the hemi-spherical segment and progressively continued deforming with the asymmetric or axisymmetric folding in cylindrical segment depending on the radius to thickness ratios and strain rates. The failure/fracture was observed in the thicker specimens at dynamic strain rates and that caused decreases in specific absorbing energy (SAE) levels. In addition, the energy partitions between the hemi-spherical segments increased at higher loading rates. Furthermore, the inertia and rate sensitivity influenced the crushing response of cylindrical segment more than that of hemi-spherical segment and inertia effect was more pronounced than the rate sensitivity at higher loading rates. Considering the thermal effects in the crushing behavior of the combined geometry shells, it was shown that the mean crushing load lowered as the temperature increased. Additionally, the percentages of increase in the crushing load were limited at lower temperatures for varying loading rates. It was shown that as the absolute temperature increased the percentage of increase in crushing load was significantly increased due to the change in deformation mode.
  • Master Thesis
    Modeling Dynamic Behavior of Metal Matrix Composites
    (Izmir Institute of Technology, 2002) Tirtom, İsmail; Güden, Mustafa
    A numerical investigation has been conducted on the strain rate dependent compression mechanical behavior of a SiC-particulate reinforced Al (2024-O) metal matrix composite. The effect of particle volume fraction on the strain rate sensitivity of the composite was determined using axisymmetric Finite Element unit cell models, where the particles are treated as elastic spheres embedded within a visco-plastic matrix, implemented in LUSAS Finite Element Analysis program. Particles are taken to be elastic, equal-sized, spherical and uniformly distributed in the matrix. The strain rate dependent constitutive behavior of the matrix material uses a linear relation between stress and strain rate formulation and is obtained from independent experimental results on the matrix. The flow stress of the composites is predicted over a range of strain rates for different particle volume fractions. Numerical results of the flow stress and strain rate sensitivity of the composite were also compared with those of experimental results, for 15% SiC particle reinforced 2024-O Al metal matrix composite. Influence of particle shape on the behavior of the MMC at high strain rates is also investigated. A unit cell, which is an elastic cylinder embedded within a visco-plastic matrix, is used. It is also shown that the rate dependent flow stress and local stress in the microstructure are influenced by particle shape. If reinforcement edge sharpness increases, local stress increases at that area. The results show that both the flow stress and the strain rate sensitivity increase with increasing volume fraction of the reinforcement due to the constraining effect of the reinforcement. Numerical calculations have shown an increased strain rate sensitivity of the composite over the matrix alloy. The discrepancy found between numerical and experimental results was finally discussed based on geometrical and microstructural parameters that might affect the composite flow stress and strain rate sensitivity.