• Transactions of Materials Processing
• /
• v.16 no.4 s.94
• /
• pp.293-298
• /
• 2007

Recently, there is a need to produce a large forged part for the flight, shipping, some energies, and military industries, etc. Therefore, an open die forging technique of cast ingots is required to obtain higher quality of large size forged parts. Cogging process is one of the primary stages in many open die forging processes. In the cogging process prior to some open die forging processes, internal cavities have to be eliminated for defect-free. The present work is concerned with the elimination of the internal cavities in large ingots so as to obtain sound products. In this study, hot compression tests were carried out to obtain the flow stress of cast microstructure at different temperature and strain rates. The FEM analysis is performed to investigate the overlap defect of cast ingots during cogging stage. The measured flow stress data were used to simulate the cogging process of cast ingot using the practical material properties. Also the analysis of cavity closure is performed by using the $DEFORM^{TM}-3D$. The calculated results of cavity closure behavior are compared with the measured results before and after cogging, which are scanned by the X-ray scanner. From this result, the criteria for deformation amounts effect on the cavity closure can be investigated by the comparison between practical experiment and numerical analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.1
• /
• pp.11-16
• /
• 2014

The effects of environment and microstructure on low cycle fatigue (LCF) behaviors of CF8M stainless steels containing 11% of ferrites were investigated in a $310^{\circ}C$ deoxygenated water environment. The reduction of LCF life of CF8M in a $310^{\circ}C$ deoxygenated water was smaller than 316LN stainless steels. Based on the microstructure and fatigue surface analyses, it was confirmed that the hydrogen induced cracking contributed to the reduction in LCF life for CF8M as well as for 316LN. However, many secondary cracks were found on the boundaries of ferrite phases in CF8M, which effectively reduced the stress concentration at the crack tip. Because of the reduced stress concentration, the accelerated fatigue crack growth by hydrogen induced cracking was less significant, which resulted in the smaller environmental effects for CF8M than 316LN in a $310^{\circ}C$ deoxygenated water.

• Korean Journal of Materials Research
• /
• v.13 no.6
• /
• pp.374-380
• /
• 2003

The effect of forging parameters, including different forging stock, strain rate and strain, on the mechanical properties of hot-forged Al 6061-T6 was investigated. The forging was conducted using either hydraulic press, crank press or hammer press, respectively, at a forging temperature of $400^{\circ}C$. When using an extruded bar as a forging stock, the tensile strength was lower for the specimens prepared by hammer forging than those by crank press forging. It was found that the coarsening of recrystallized grain was responsible for the decrease in tensile strength with hammer forging. Systematic studies on the effects of strain and strain rate on the tensile properties of hot-forged Al 6061-T6 products using extruded bar as a forging stock further suggested that the coarsening of recrystallized grains and$ Mg_2$Si precipitates complexed the observed trends in the tensile behavior. In case of hot forging with continuous cast bar as a forging stock, on the other hand, the mechanical properties of the specimen were largely improved with hammer press compared to those with crank press, which appeared to be due to the homogenization of microstructure.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.106.2-106.2
• /
• 2012

Ti-Ni합금은 CsCl구조의 B2상, monoclinic 구조의 B19'(M)상과 rhombohedral 구조의 R상(R)이 나타난다고 알려져 있고, 이들 상의 변태에 의해 열탄성 마르텐사이트와 응력유기 마르텐사이트에 의한 형상기억효과와 초탄성 효과를 가지고 있다. 또한 Ti-Ni 합금은 우수한 형상기억특성을 가질 뿐만 아니라 생체적합성, 가공성 및 내식성 등이 뛰어나 공업분야 및 생체분야에서 폭 넓게 활용되고 있다. Ti-Ni합금의 형상기억특성은 냉간가공 후 어닐링 처리의 온도와 시간에 따른 matrix 내 Ni의 농도, 석출물의 밀도와 크기, 전위밀도와 전위주위의 응력장에 의해 영향을 받는다고 알려져 있다. 본 연구에서는 Ti-Ni합금의 형상기억 특성 및 변태온도에 미치는 영향을 조사하기 위해 다양한 냉간가공률의 시료를 제작하여 다양한 온도에서 Annealing 처리를 하여 냉간가공률 및 Annealing 온도가 형상기억특성에 미치는 영향을 조사하였다. Ti-50.4 at.% Ni 합금은 진공 아크 용해로에서 용해 하였으며, 용해된 Ingot는 열간단조 및 열간 압출한 후 냉간 인발과 중간온도에서 어닐링을 반복하면서 직경 0.5mm의 선재로 만들었다. 최종적으로 제작한 선재의 냉간가공률은 9.5%, 18.2%, 34.5%, 45% 이었다. 각 시편은 5X10-5torr의 진공으로 석영관에 진공 봉입하여 각각 673K, 723K, 783K에서 1hr 열처리 하였다. 합금의 형상기억특성과 변태온도는 DSC에 의해 조사되었다. DSC 측정 결과, 냉간가공률이 증가함에 따라 마르텐사이트 변태 온도는 감소하였고, 어닐링 온도가 증가함에 따라 마르텐사이트 변태 온도는 증가하였다. 또한 가공률이 증가하여도 R상 변태온도는 큰 변화가 없었고, Annealing온도가 증가함에 따라 R상 변태온도는 감소하였다. 또한, 형상기억특성은 인장시험기를 이용한 정하중 열싸이클 테스트를 이용하여 평가 하였다. 냉간 가공률이 증가함에 따라 안정한 형상기억특성을 나타내었다.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
• /
• 2009.05a
• /
• pp.109-112
• /
• 2009

The purpose of this study was to examine the differences in the brain activation evoked by music arranged in major and minor key used with an identical motion film during the fMRI testing. A part of the audio-visual combinations composed by Iwamiya and Sano were used for the study stimuli. This audio- visual clip was originally developed by combining a small motion segment of the animation "The Snowman" and music arranged in both major and minor key from the original jazz music "Avalon" rewritten in a classical style. Twenty-seven Japanese male graduate and undergraduate students participated in the study. Brain regions more activated by the major key than the minor key when presented with the identical motion film were the left cerebellum, the right fusiform gyrus, the right superior occipital, the left superior orbito frontal, the right pallidum, the left precuneus, and the bilateral thalamus. On the other hand, brain regions more activated by the minor key than the major key when presented with the identical motion film were the right medial frontal, the left inferior orbito frontal, the bilateral superior parietal, the left postcentral, and the right precuneus. The study showed a difference in brain regions activated between the two different stimulus (i.e., major key and minor key) controlling for the visual aspect of the experiment. These findings imply that our brain systematically generates differently in the way it processes music written in major and minor key(Supported by the User Science Institute of Kyushu University, Japan and the Korea Science and Engineering Foundation).

• Journal of the Korean Society of Propulsion Engineers
• /
• v.18 no.4
• /
• pp.1-8
• /
• 2014

Overexpanded flow of an axisymmetric thruster nozzle is numerically simulated to investigate effects of nozzle pressure ratio (NPR) on the shock structure and thrust performance. The Reynolds-averaged Navier-Stokes equations with k-${\omega}$ SST turbulence model are solved utilizing FLUENT solver. As the NPR is raised, thrust performance monotonically increases with the shock structure and flow-separation point being pushed toward the nozzle exit. It is also discussed that the flow structure at nozzle-exit plane which is immediately affected by a position of nozzle-interior shocks and expansion waves, has strong influence upon the thrust performance of thruster nozzle.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.5
• /
• pp.1192-1202
• /
• 1994

Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

• Design & Manufacturing
• /
• v.14 no.3
• /
• pp.17-22
• /
• 2020

As devices such as smartphones, tablet PC, and wearable devices have been miniaturized, the connectors that go into the devices are also designed to be very small. The connector combines the plug and the receptacle to transfer electricity. As devices are miniaturized, the contact shape is formed by partially thinning the thickness of the raw material of the terminal in order to lower the coupling height of the plug and receptacle. The product used in this study is a receptacle terminal used for 0.4mm pitch board to board connector among fine pitch connectors. When the material thickness is reduced by forging the receptacle terminal, the width change of the pin is checked. To reduce the thickness of the material by forging, pre-notching is applied in the first step, forging in the second step, and notching in the third step. After forming the width dimension of the pin to 0.28 mm in the pre-notching process, in the forging process, the material thickness 0.08 mm and 0.02 mm (25%) were forged and the thickness was changed to 0.06 mm and the width change amount of the pin was measured. The facility produced 10,000 pieces at 400 SPM using a Yamada Dobby (MXM-40L) press, and thirty pins were measured and the average value was shown. After forging by using C5210-H (HP) and NKT322-EH, which are frequently used in connectors, analyze the amount of change in each material. The effect of punching oil on forging is investigated by appling FM-200M, which is highly viscous, and FL-212, fast drying oil. This study aims to minimize mold modification by predicting the amount of material change after forging.

• Journal of Korean Society of Steel Construction
• /
• v.11 no.2 s.39
• /
• pp.109-116
• /
• 1999

This paper presents an experimental study on the behavior of CFT Column to H-Beam Endplate Connections with penetrated H/T bolts under monotonic loading. The object of this study is to estimate accurately the effect about the thickness of endplate and the arrangement of H/T bolts which was not got a grip on the results reported in the previous paper. Main parameters are the thickness of endplates (12mm, 16mm) and the arrangemement of H/T bolts (EP1, EP2, EP3 Type). The experimental results compared and analysed. 1) The specimens were classified by Bjorhovde's and EC3's method. 2) A formula to predict the ultimate moment of connection was derived based on the T-stub model, and theoretical value $(_tM_u)$ computed by the formula corresponded to the experimental value $(_eM_u)$.

• Journal of Korean Society of Steel Construction
• /
• v.11 no.2 s.39
• /
• pp.241-241
• /
• 1999

The analysis and design of steel frames are usually carried out under the assumption that the connections of beam-to-column are either fully rigid or ideally pinned. However the connections actually show semi-rigid behavior in many cases. The authors investigated the structural behavior of simi-rigid connection with reformed T-stub by using of SM490 steel. The objective of the study is to investigate the structural behavior of the beam-to-column semi-rigid connection with reformed T-stub, which is made of SS400 steel. The beam-to-column connections by using reformed T-stubs were tested under monotonic loading and cyclic loading condition. The possibility of application of semi-rigid connections with reformed T-stubs was ascertained from test results.