• 대한기계학회논문집A
• /
• 제40권8호
• /
• pp.751-757
• /
• 2016

본 논문은 스테어케이스법을 사용하여 크랭크 스로 부품용 S34MnV강의 피로한도의 신뢰도를 평가하는 것이다. 크랭크 스로 부품의 소재는 S34MnV이며, 뜨임 및 풀림 열처리된 단조강이다. 본 연구에서는 설계피로강도의 신뢰도를 예측하기 위해 축 하중 일정진폭 피로시험을 수행하였다. 시험편은 평균응력 0 MPa의 동일한 응력부하를 적용하였고, 즉 응력비는 -1로 하였다. 피로시험 결과는 Dixon-Mood 접근법으로 평가하였다. 스테어케이스법에 의해 예측된 피로강도의 평균과 표준편차는 각각 296.3 MPa 및 10.6 MPa로 나타났다. 마지막으로 어떤 임의의 파손 확률에 대한 피로강도의 신뢰도를 예측하였다. 본 연구에서 제안한 예측법은 단조강의 설계 최적화를 위한 피로강도 값을 결정할 수 있다.

• 대한물리의학회지
• /
• 제12권2호
• /
• pp.91-101
• /
• 2017

PURPOSE: The aim of this study was to verify the effect of trunk strengthening exercise using oscillation by comparing trunk muscle thickness, as well as balance of healthy adults during exercises performed with an oscillatory device and non-oscillatory device. METHODS: Twenty-two participants were randomly assigned to one of two groups: the trunk strengthening exercise using oscillation (TSEO) group (n=11) or the trunk strengthening exercise using non-oscillation (TSEN) group (n=11). Subjects in all groups performed the exercises three days per week for 6 weeks. All subjects performed four types of exercises: pull over, seated twist, power push, and diagonal power plank. Trunk muscle thickness of the rectus abdominis (RA), internal oblique (IO), external oblique (EO), transverse abdominis (TrA), and multifidus (MT) were measured with an ultrasonography. The balance ability were evaluated using the Romberg test with eyes open, eyes closed, one-leg standing test (OLST), and limits of stability (LOS). All tests were performed before the intervention, as well as after 6 weeks and 8 weeks of exercises. RESULTS: There was a significant difference of RA, IO, TrA, and MT according to the main effect of the time (p<.05). There was a significant difference of IO and LOS according to interaction effect between the time and group (p<.05). CONCLUSION: As intended, the cyclic forces induced by the oscillating device did increase trunk muscle thickness. However, the effect was limited and significant only for the IO muscle. Combining trunk strengthening exercise with oscillation appears to be more effective in improving dynamic balance.

• 한국콘텐츠학회논문지
• /
• 제15권3호
• /
• pp.427-437
• /
• 2015

콘크리트는 인장거동에 취약하므로 적절한 보강재를 필요로 한다. 또한 시멘트 클링커 생산시 발생하는 $CO_2$로 인해 시멘트 사용량을 줄이려는 연구가 시도되고 있다. 본 연구에서는 폴리프로필렌 섬유와 왕겨재를 혼입한 콘크리트의 공학적 성능을 평가하였다. 섬유재는 0.125~0.375%의 수준을, 왕겨재는 0~20% 치환률을 고려하여 콘크리트 배합을 준비하였으며, 압축강도, 쪼갬인장강도, 휨강도와 균열폭, 내충격성, 인발특성을 평가하였다. 또한 섬유재 혼입률, 섬유재 길이, 왕겨재의 혼입률을 고려하여 실험결과를 분석하였다. 인장특성에 대해서는 섬유재의 혼입량이, 강도특성에서는 왕겨재의 혼입률이 지배적이었으며, 0.125%의 섬유재 혼입과 10% 왕겨재 치환인 배합에서 가장 효과적인 공학적 특성이 발현되었다. 적절한 왕겨재 및 섬유재의 혼입은 다양한 공학적 특성을 강화시킬 뿐 아니라 친환경적인 측면에서도 유리하다고 판단된다.

• Steel and Composite Structures
• /
• 제35권4호
• /
• pp.463-474
• /
• 2020

In this paper, the influence of adding multi-walled carbon nanotube (MWCNT) on the pull behavior of steel and GFRP bars in ultra-high-performance concrete (UHPC) was examined experimentally and numerically. For numerical analysis, 3D nonlinear finite element modeling (FEM) with the help of ABAQUS software was used. Mechanical properties of the specimens, including Young's modulus, tensile strength and compressive strength, were extracted from the experimental results of the tests performed on standard cube specimens and for different values of weight percent of MWCNTs. In order to consider more realistic assumptions, the bond between concrete and bar was simulated using adhesive surfaces and Cohesive Zone Model (CZM), whose parameters were obtained by calibrating the results of the finite element model with the experimental results of pullout tests. The accuracy of the results of the finite element model was proved with conducting the pullout experimental test which showed high accuracy of the proposed model. Then, the effect of different parameters such as the material of bar, the diameter of the bar, as well as the weight percent of MWCNT on the bond behavior of bar and UHPC were studied. The results suggest that modifying UHPC with MWCNT improves bond strength between concrete and bar. In MWCNT per 0.01 and 0.3 wt% of MWCNT, the maximum pullout strength of steel bar with a diameter of 16 mm increased by 52.5% and 58.7% compared to the control specimen (UHPC without nanoparticle). Also, this increase in GFRP bars with a diameter of 16 mm was 34.3% and 45%.

• Advanced Composite Materials
• /
• 제17권3호
• /
• pp.277-299
• /
• 2008

High quality and expedient processing repair methods are necessary to enhance the service life of bridge structures. Deterioration of concrete can occur as a result of structural cracks, corrosion of reinforcement, and freeze.thaw cycles. Cost effective methods with potential for field implementation are necessary to address the issue of the vulnerability of bridge structures and how to repair them. Most infrastructure related applications of fiber-reinforced plastics (FRPs) use traditional hand lay-up technology. The hand lay-up is tedious, labor-intensive and relies upon personnel skill level. An alternative to traditional hand lay-up of FRP for infrastructure applications is Vacuum Assisted Resin Transfer Molding (VARTM). VARTM uses single sided molding technology to infuse resin over fabrics wrapping large structures, such as bridge girders and columns. There is no work currently available in understanding the interface developed, when VARTM processing is adopted to wrap fibers such as carbon and/or glass over concrete structures. This paper investigates the interface formed by carbon fiber processed on to a concrete surface using the VARTM technique. Various surface treatments, including sandblasting, were performed to study the pull-off tensile test to find a potential prepared surface. A single-lap shear test was used to study the bond strength of CFRP fabric/epoxy composite adhered to concrete. Carbon fiber wraps incorporating Sikadur HEX 103C and low viscosity epoxy resin Sikadur 300 were considered in VARTM processing of concrete specimens.

• International Journal of Automotive Technology
• /
• 제6권2호
• /
• pp.183-190
• /
• 2005

During normal operating conditions, a motor vehicle is constantly subjected to a variety of forces, which can adversely affect its straight-ahead motion performance. These forces can originate both from external sources such as wind and road and from on-board sources such as tires, suspension, and chassis configuration. One of the effects of these disturbances is the phenomenon of vehicle lateral-drift during straight-ahead motion. This paper examines the effects of road crown, tires, and suspension on vehicle straight-ahead motion. The results of experimental studies into the effects of these on-board and external disturbances are extremely sensitive to small changes in test conditions and are therefore difficult to guarantee repeatability. This study was therefore conducted by means of computer simulation using a full vehicle model. The purpose of this paper is to gain further understanding of the straight-ahead maneuver from simulation results, some aspects of which may not be obtainable from experimental study. This paper also aims to clarify some of the disputable arguments on the theories of vehicle straight-ahead motion found in the literature. Tire residual aligning torque, road crown angle, scrub radius and caster angle in suspension geometry, were selected as the study variables. The effects of these variables on straight-ahead motion were evaluated from the straight-ahead motion simulation results during a 100m run in free control mode. Examination of vehicle behavior during straight-ahead motion under a fixed control mode was also carried out in order to evaluate the validity of several disputable arguments on vehicle pull theory, found in the literature. Finally, qualitative comparisons between the simulation results and the test results were made to support the validity of the simulation results.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 추계학술대회 논문집
• /
• pp.380-386
• /
• 2008

The development of a new railway vehicle is under progress through the Next Generation High-Speed Rail Development Project in Korea. Its aim is to develope fundamental technology of the vehicle that can run over 400km/h. The new distributed traction bogie system, 'HEMU'(High-speed Electric Multiple Unit), will be used and is different from that of previously developed high speed railway vehicles. Previous vehicles adopted push-pull type system, which means one traction-car drives rest all of the vehicle. Due to the difference, investigation on dynamic behavior and its safety evaluation are necessary, as a part of verification of the design specification. In the paper, current progresses of researches are presented. And the High-Speed Railway vehicle system is evaluated for a dynamic characteristic simulation. Proper dynamic models including air-suspension system, wheel-rail, bogie and car-body is developed according to the vehicle simulation scenario. The basic platform for the development of dynamic solver is prepared using nodal, modal coordinate system and wheel-rail contact module. Operating scenario is prepared using commercial dynamic analysis program and used for development of dynamic model, which contains many parts such as carbodies, bogies and suspension systems. Furthermore, international safety standard is applied for final verification of the system. Finally, the reliability of the dynamic model will be verified with test results in the further researches. This research will propose a better solution when test results shows a problem in the parts and elements. Finally, the vehicle that has excellent performance will be developed, promoting academic achievement and technical development.

• 대한건축학회논문집:구조계
• /
• 제34권1호
• /
• pp.41-51
• /
• 2018

In case of evaluating the bond stress of a void deck plate using a wire steel, there is no standard formula considering both the influence on the void and the type of the reinforcing bar. Therefore we proposed a model equation considered the bond characteristics of the void deck plate. A total of 46 specimens was carried out a direct pull-out test and the test variables were the presence of a void body, type of reinforcing bar, the inner cover thickness according to the location of reinforcing bars and bond region. As a result of the comparison between the steel bar and steel wire, the bond stress of the steel wire with the relative rib area of 0.071 is 4.5 ~ 28.58% lower than that of the steel bar with 0.092 and the bond stress reduction rate increases when the inner cover thickness is insufficient. In the case of the inner cover thickness of $1.7d_b$ and $2.7d_b$, the bond stress was reduced to 48.7 ~ 68.4%. In the inner cover thickness was $4.9d_b$ and $5.2d_b$, the bond stresses were equivalent to those of the solid specimens. It was confirmed that the average bond stress and strain were affected by the inner cover thickness. Therefore the predicted model for one module of the void deck plate is proposed and verified by considering the bond characteristics of the void deck plate.

• 대한통합의학회지
• /
• 제10권4호
• /
• pp.93-102
• /
• 2022

Purpose : The purpose of this study was to analyze the change in thickness of transvers abdominis, internal oblique, and external oblique when virtual reality based ring fit adventure is applied to young adults in order to investigate the effect of ring fit adventure on core stabilization. Methods : 30 subjects participated in the experiment. Subjects were randomly assigned to two groups. 15 subjects performed ring fit adventure core exercise (experimental group) and 15 subjects bridge and dead bug exercise (control group). The ring fit adventure core exercise program consists of 6 types, 1) bow pull, 2) overhead lunge twist, 3) pendulum bend, 4) seated ring raise, 5) plank, 6) warrior III pose. Each exercise was performed for 5 minutes, for a total of 30 minutes. The bridege and dead bug exercise were performed for 15 minutes each for a total of 30 minutes. All interventions were performed 3 times a week for 4 weeks. Thickness of the abdominal muscles was measured with a ultrasound. The paired t-test was used to compare the thickness of the transverse abdominis, internal oblique, and external oblique before and after intervention, and the comparison between groups was analyzed using the independent t-test. Results : As a result, in the experimental group, thickness of transverse abdominis and internal oblique increased significantly (p<.05), but external oblique decreased significantly (p<.05), and in the control group, thickness of transverse abdominis, internal oblique, and external oblique increased significantly (p<.05). There was a significant difference in external oblique in the difference between groups (p<.05). Conclusion : These study results showed that core exercise using ring fit adventure can reduce external oblique and increased selective muscle activity of transverse abdominis and internal oblique of the deep abdominal muscles, so it is meaningful as an effective intervention for core stabilization.

• 대한토목학회논문집
• /
• 제26권4A호
• /
• pp.775-785
• /
• 2006

본 논문은 우수한 부착성능과 더불어 단순한 공정으로 생산이 가능한 GFRP 보강근의 표면성형 기법을 제시하였다. 논문에는 제안하고자하는 표면성형기법에 대한 내용과 개발된 보강근의 콘크리트 부착성능에 대하여 언급하였다. 본 논문에서 제안하는 표면성형공법은 에폭시레진에 초단섬유인 milled glass fibers를 혼입하여 GFRP 보강근의 외부에 프레스 성형하는 공법이다. milled fibers의 적적한 혼합비를 결정하기 위하여 다양한 혼입비로 제작된 경화된 에폭시 시편의 압축강도실험과 다양한 혼입비의 표면형상을 갖는 부착시험편의 pull-out 실험이 수행되었다. 실험결과, 정적하중하에서 뿐 아니라 환경하중 재하상태에서도 milled fibers의 혼입량이 증가할수록 콘크리트와의 부착성능이 증진됨을 확인됨으로써 본 공법의 효용성을 검증하였다.