Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis The Deformation Rate Sensitivities of Additively and Conventionally Fabricated 316l Alloys(01. Izmir Institute of Technology, 2021) Güden, Mustafa; Enser, Samed; Güden, Mustafa; 01. Izmir Institute of Technology; 03.10. Department of Mechanical Engineering; 03. Faculty of EngineeringThe compression stress-strain behavior of a Scanning Laser Melt 316L (SLM-316L) and an annealed and extruded commercial 316L (C-316L) were determined between 1x10-3 s-1 and 2500-3150 s-1. SLM-316L deformed by twinning and slip, while C-316L by martensitic transformation and slip with no fracture until about 0.51 strain. The higher yield strength of SLM-316L than C-316L was attributed to the higher dislocation density of SLM-316L. The higher work hardening rate of C-316L alloy was proved due to the higher resistance of martensite plate than twin boundary to the dislocation motion. As the strain rate increased, both alloys showed increased flow stresses. However, the rate sensitivities declined as the strain increased due to the adiabatic heating at high strain rates. The Johnson and Cook flow stress material models of both alloys were further determined for the adiabatic and isothermal conditions. The martensite formation in C-316L specimens and twinning formation in SLM-316L alloys decreased at high strain rates compared to quasi-static strain rates. The XRD spectra of C-316L also confirmed the reduced martensite formation at high strain rates. The reduced twin and martensite formation at high strain rates were attributed to the increased stacking fault energy due to the adiabatic heating of the test specimens. The increase of stacking fault energy at high strain rates promoted a higher fraction of the deformation by slip. Lastly, the reloading tests revealed a strain-rate history effect in SLM-316L and no strain-rate history effect in C-316L.Master Thesis Modelling the Damage Formation of Bolted Carbon Fiber Reinforced Epoxy Composite Joints at Increasing Strain Rates(01. Izmir Institute of Technology, 2021) Güden, Mustafa; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe bearing strength of a carbon fiber reinforced/epoxy unidirectional composite joint incorporating a single hex bolt fastener was investigated under quasi-static and dynamic loads experimentally and numerically with two different bolt torques, 2.5 N m and 10 N m. The tests were conducted with neat fit clearance and without washer. The quasi-static tests were conducted at 3.33x10-5 and 1.66 x10-3 m s-1 according to the ASTM D5961 Procedure C. The dynamic tests were conducted in at Tension Split Hopkinson Pressure Bar (TSHPB) at 12.68 m s-1 using a specially designed specimen grip to ensure the same conditions as the quasi-static tests. Three dimensional explicit finite element models of bearing tests were developed in the LS-DYNA and the composite was modelled using the MAT_162 composite material model incorporating the strain rate effects. At the quasi-static velocities, a relatively low strain rate dependence of bearing peak force was found with almost no effect of applied bolt torque. In the TSHPB tests, the bearing force increased by 57% of those of quasi-static tests. The deformation mode also altered in dynamic tests and the increase of the bolt torque resulted with increasing the bearing peak force by 5%.