Sintering and Microstructure Characteristics of 42CrMo4 Steel Processed by Spark Plasma Sintering

Ridvan Yamanoglu,William Bradbury,Eugene A. Olevsky,Randall M. German 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.5

Rapidly solidified micron sized 42CrMo4 steel powder with a size range of 150-250 μm produced by plasma rotating electrode process was consolidated using a recently developed spark plasma sintering (SPS) process. The relationship between sintering parameters (temperature and soaking time) and microstructural properties was investigated. The effect of slow and high heating regimes on the consolidation of sintered compacts has been also investigated. Maximum relative density (99.2%) was obtained at 1000 °C, under 50 MPa pressure, with 8 min holding time and 200 °C/min heating rate. The microstructure of sintered steel was influenced by carburization occuring inside the graphite SPS process die. The diffusion of carbon produced martensite structure near the surface region and hardened the surface. This effect was investigated in detail using optical microscopy and hardness measurement. Scanning electrone microscopy was also used to examine the fracture surface of sintered compacts. High heating rate promoted the relative density at low temperature compared to high temperature.

In-plane vibrations of cracked slightly curved beams

H. Ridvan Oz 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.6

In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Brüel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending,extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.

In-plane vibrations of cracked slightly curved beams

Oz, H. Ridvan Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.6

In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Bruel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending, extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.

ENERGY ON A PARTICLE IN DYNAMICAL AND ELECTRODYNAMICAL FORCE FIELDS IN LIE GROUPS

( Talat Korpinar ),( Ridvan Cem Demirkol ) 호남수학회 2018 호남수학학술지 Vol.40 No.2

In this study, we firstly define equations of motion based on the traditional model Newtonian mechanics in terms of the Frenet frame adapted to the trajectory of the moving particle in Lie groups. Then, we compute energy on the moving particle in resultant force field by using geometrical description of the curva-ture and torsion of the trajectory belonging to the particle. We also investigate the relation between energy on the moving particle in different force fields and energy on the particle in Frenet vector fields.

Preform-Based Production of Al2O3-Reinforced Aluminium Matrix Composites by Using Various Modification Techniques

Kubilay Ozturk,Ridvan Gecu,Ahmet Karaaslan 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

Metal matrix composites have a wide range of applications due to their lightweight, high strength and high wear resistance.In this study, Al2O3-reinforced AA7075 matrix composites were produced by using liquid metal infiltration method in twostages. In the first stage of the production, preforms were manufactured by using Al2O3particles and different binders. Someof the preforms were sintered and some were not sintered. In the second step, liquid metal infiltration was performed on bothsintered and not sintered samples. Some preforms were preheated before the infiltration and some were directly subjected tothe liquid metal infiltration. The casting process was carried out in two different ways: (1) pouring the molten metal into thefired mould and (2) in situ melting of the metal during the mould firing. Fabricated composites were characterized by XRD,light metal microscopy, SEM, EDS, Brinell hardness and ball-on-disc type wear tests. When the microstructural, mechanicaland tribological properties were taken into account, preheating and sintering preforms before casting were determinedas performing best with the hardness of ~ 150 HB and the wear rate of 1.1 × 10−4 mm3/(N m), whereas the in situ meltingcaused decrease in the mechanical strength and wear resistance because of excessive oxidation.

A New Approach On The Curvature Dependent Energy For Elastic Curves in a Lie Group

Talat Korpinar,Ridvan Cem Demirkol 호남수학회 2017 호남수학학술지 Vol.39 No.4

Elastica is known as classical curve that is a solution of variational problem, which minimize a thin inextensible wire's bending energy. Studies on elastica has been conducted in Euclidean space firstly, then it has been extended to Riemannian manifold by giving different characterizations. In this paper, we focus on energy of the elastic curve in a Lie group. We attepmt to compute its energy by using geometric description of the curvature and the torsion of the trajectory of the elastic curve of the trajectory of the moving particle in the Lie group. Finally, we also investigate the relation between energy of the elastic curve and energy of the same curve in Frenet vector fields in the Lie group.

COVID-19 and Plasmodium ovale Malaria: A Rare Case of Co-Infection

Bilge Caglar,Ridvan Karaali,Ilker Inanc Balkan,Bilgul Mete,Gokhan Aygun 대한기생충학열대의학회 2021 The Korean Journal of Parasitology Vol.59 No.4

A NEW APPROACH ON THE CURVATURE DEPENDENT ENERGY FOR ELASTIC CURVES IN A LIE GROUP

Korpinar, Talat,Demirkol, Ridvan Cem The Honam Mathematical Society 2017 호남수학학술지 Vol.39 No.4

Elastica is known as classical curve that is a solution of variational problem, which minimize a thin inextensible wire's bending energy. Studies on elastica has been conducted in Euclidean space firstly, then it has been extended to Riemannian manifold by giving different characterizations. In this paper, we focus on energy of the elastic curve in a Lie group. We attepmt to compute its energy by using geometric description of the curvature and the torsion of the trajectory of the elastic curve of the trajectory of the moving particle in the Lie group. Finally, we also investigate the relation between energy of the elastic curve and energy of the same curve in Frenet vector fields in the Lie group.

Intestinal Obstruction Due to a Mesenteric Cyst

Ibrahim Barut,Omer Ridvan Tarhan,Metin Ciris,Yusuf Akdeniz,Mahmut Bulbul 연세대학교의과대학 2004 Yonsei medical journal Vol.45 No.2

Mesenteric cysts are rarely thought of, may be difficult to diagnose, and are usually asymptomatic except when complicated. Intestinal obstruction is a rarely reported complication of these cysts. A case of mesenteric cyst that was causing obstruction of the large bowel is presented, along with a review of the literature.

ENERGY ON A PARTICLE IN DYNAMICAL AND ELECTRODYNAMICAL FORCE FIELDS IN LIE GROUPS

Korpinar, Talat,Demirkol, Ridvan Cem The Honam Mathematical Society 2018 호남수학학술지 Vol.40 No.2

In this study, we firstly define equations of motion based on the traditional model Newtonian mechanics in terms of the Frenet frame adapted to the trajectory of the moving particle in Lie groups. Then, we compute energy on the moving particle in resultant force field by using geometrical description of the curvature and torsion of the trajectory belonging to the particle. We also investigate the relation between energy on the moving particle in different force fields and energy on the particle in Frenet vector fields.