Ibrahim Sevim

Abrasive wear behaviour of bio-active glass ceramics containing apatite

In this study, abrasive wear behaviour of bio-active glass ceramic materials produced with two different processes is studied. Hot pressing process and conventional casting and controlled crystallization process were used to produce bio-active ceramics. Fracture toughness of studied material was calculated by fracture toughness equations using experimental hardness results of the bio-active glass ceramic material. Two fracture toughness equations in the literature were used to identify the wear behaviour of studied ceramics. Wear resistance results that identified with both of the equations were similar. The results showed that the abrasive wear resistance of the bio-active glass ceramics produced with hot pressing process was found to be higher than that of the ceramics produced by conventional casting and controlled crystallization process.

Effect of Aging Treatment on Surface Roughness, Mechanical Properties, and Fracture Behavior of 6XXX and 7XXX Aluminum Alloys

The effect of aging treatment on the surface roughness and mechanical properties of AA6061 and AA7075 alloys was studied. Microhardness and tensile tests were used to investigae the mechanical properties. X-ray diffraction analysis was used to investigate the surface of the specimens. Furthermore, after tensile tests fractured surfaces were examined with scanning electron microscopy. An atomic force microscope was employed for analysis of the effect of aging treatment on surface roughness. Higher surface roughness with an increase in the volume fraction of the precipitate was revealed.

Fracture Toughness of Friction Stir-Welded Lap Joints of Aluminum Alloys

The aim of this study is to determine the fracture toughness of friction stir-welded (FSW) lap joints of aluminum alloys. FSW lap joints of AA 2014 and AA 6063 aluminum alloy plates were performed on a conventional semiautomatic milling machine. FSW lap joints were produced on alloy plates. Fracture toughness of FSW lap joints were calculated from the results of tensile shearing tests. New empirical equations were developed for fracture toughness and energy release rate based on the relation between the hardness and fracture toughness values. Fracture toughness of FSW lap joints increases exponentially as the hardness reduces. The results of the experiments showed that the amount of Si content in Al alloys affects the fracture toughness of the FSW lap joints.

Nucleus geometry and mechanical properties of resistance spot welded coated-uncoated DP automotive steels

In this study, mechanical properties of resistance spot welding of DP450 and DP600, galvanized and ungalvanized automotive sheets have been investigated. The specimens have been joined by resistance spot welding at different weld currents and times. Welded specimens have been examined for their mechanical, macrostructure and microstructure properties. Depending on the weld current and time, effects of zinc coating on tensile properties, microhardness values as well as microstructure nugget geometry and nucleus size ratio have been investigated. X-ray diffraction analysis has been used to investigate the phase that formed at the joint interface. Result of the experiment show that nugget diameter, indentation depth and tensile load-bearing capacity are affected by weld parameters. Coating prevents full joining at low parameters. Microhardness increased in heat-affected zone and weld metal.

Effect of Abrasive Particle Size on Abrasive Wear Resistance in Otomotive Steels

If one of the surfaces which are in touch is rough and hard, it chips the other surface due to relative motion or touching forces. The wear is called two-body abrasive wear. If there are free abrasive particles between the two bodies, the wear is called three-body abrasive wear. The free abrasive particles may be external material dust or the remains of chipping. Usually, the wear starts as a two-body abrasive or adhesive wear and then becomes a threebody wear as dust form between the two surfaces due to external particles, chipping remains, or oxide particles. In three-body abrasive wear, wear rate increases as diameter of abrasive particles increases. Gouging, high stress abrasion and low stress abrasion are types of three-body abrasive wear [1-3].

Investigation of parallel axis gear test rigs and selection criterias to design

Gears are used in different industries from machine and equipments manufacturing to automotive industry, from energy industry such as steam and hydraulic turbines, wind turbines to aeronautics such as helicopter and aero plane industries. There is an increasing demand for gears which work at high speeds and carry high loads, so there is more need for gear research and development activities on gear subject like wear, fatigue, transmission failures, failures based on vibration and noise. In this study, parallel axis gear test rigs have been investigated and selected to design.

Newly revealed features of fracture toughness behavior of spot welded dual phase steel sheets for automotive bodies

Abstract Fracture toughness is one of the parameters, which are used to estimate the fatigue life of resistance spot-welded (RSW) joints. A spot-welded pair is affected by the shear stress of the weld zone when it is exposed to tensile load. Repetitive loads reduce the fatigue life of the spot weld, and the material splits at the spot-welded region. This study investigates the effect of welding current, weld time and nucleus size ratios on the fracture toughness of RSW of galvanized DP450 steels having 1.0 mm thickness. The specimens were joined by spot welding at different welding currents and times. Welding processes were carried out using 3, 5, 7 and 9 kA welding current and 10, 20, 30 and 40 cycles (1 cycle = 0.02 s) weld time and the electrode pressure was fixed at 600 MPa. All series of specimens were exposed to tensile shear test in order to determine the fracture toughness. The fracture toughnesses for all series of RSW joints were calculated by using the formula given in the literature. The nugget diameters, core sizes and their heights were measured via an optical microscope. The Vickers microhardness measurement was carried out on the weld nugget, heat affected zone (HAZ) and base metal. Nucleus size ratios were calculated. The results of the study demonstrated that the fracture toughness of RSW depended not only on the nugget diameter D, but also sheet thickness t, tensile rupture force F, hardness H and nucleus size ratios hn/dn.