Master Degree / Yüksek Lisans Tezleri

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

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Subject: search.filters.subject.Finite element analysis

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  • Master Thesis
    Investigation of the Fatigue Behaviour of Metallic Components Used in Plate Heat Exchangers Under Variable Dynamic Loads
    (Izmir Institute of Technology, 2020) Kandemir, Sinan; Kandemir, Sinan; Kandemir, Sinan; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water without mixing of them with a high efficiency. Over the lifetime of the PHE, cyclic pressures act on the brazing points and the plates, and this may lead to fatigue failure. The fatigue behaviours of the PHEs which are designed by using copper brazed 316L and 304L stainless steels, were investigated in this thesis by performing strain based fatigue tests to also seek the feasibility of the use of 304L stainless steel in PHE production to reduce the cost. Besides, the microstructural investigation of the brazed regions was conducted and, the tensile tests for both non-brazed and brazed steel specimens were performed in order to determine the mechanical properties of the samples. The fatigue tests were carried out with twelve specimens for each sample groups at four different load levels as displacement (strain) controlled with a stress ratio of R=0 and 5 Hz frequency. Finite Element Analysis (FEA) was performed to determine the strain distribution on the plates of PHEs during their operation to estimate the lifetime of PHEs by using the generated lifetime curves based on the fatigue tests. Consequently, it was obtained that the ultimate tensile strength and fracture strain of non-brazed steel specimens are higher than those of the brazed specimens. The Scanning Electron Microscopy (SEM) analysis shows that; copper can diffuse into 316L easier than 304L and the use of copper foil with 50 µm thickness results in more defect at brazing regions compared to 100 µm thickness. Hereunder the fatigue test results, Weibull Analysis was performed and the fatigue life curves were generated. It was found that 316L brazed joint has approximately 33 times greater fatigue life than 304L brazed joint and filler metal thickness is more likely to have a linear relationship with fatigue life. Finally, fatigue lives of each sample group were calculated based on the loads determined by FEA. The results suggest that either 316L or 304L stainless steels can be used as PHE material as both materials satisfy the lifetime requirement of 15 years which was preliminarily defined by Bosch Thermotechnology (TT).
  • Master Thesis
    Development of Mr-Fluid Based Semi-Active Dampers To Be Used in Haptic Devices
    (Izmir Institute of Technology, 2017) Karabulut, Mehmet Görkem; Dede, Mehmet İsmet Can; Karabulut, Mehmet Görkem; Dede, Mehmet İsmet Can; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this thesis, development of a novel Magneto-Rheological (MR) fluid based brake system is described which is designated to be used in kinesthetic haptic devices. The new design of MR-brake system consists of two identical directional brakes and with this feature, it presents a solution to the stiction problem that occurs when the MR-brake is activated which constrains the rotational motion in both direction. This constraint of the motion results in developing a feeling that the user is stuck in the virtual wall. By using two independently controlled brakes in a system, the rotational brake direction is controlled and thus the motion of the handle is constrained in one direction while the user is free to move the handle in the reverse direction. MR-brake is developed from a conceptual design to the final design by applying a design optimization method. This method incorporates the use of Finite Element Analysis (FEA) and mathematical model of the system. Using this method, it is possible to predict the performance of the design to check if it meets the requirements that are specified by considering the future use of the device. After manufacturing a prototype, its performance is experimentally validated in a test rig which is also constructed in the scope of this thesis study. Experimental study includes two sections as characterization and frequency response test. As a result, the prototype is characterized with constructing the torquecurrent relation, which clearly shows the expected hysteresis in operation. The control model of the system is mathematically modeled with %95 accuracy ratio using the obtained experimental results. Experimental results show that the maximum brake torque of the system is 3.84 Nm and the minimum torque value is 0.15 Nm. The frequency response of the system is experimentally investigated and using this result, the system’s transfer function is estimated and its bode diagram is drawn. According to this result, the bandwidth of the system is calculated to be 63 rad/s.