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Fretting Fatigue Behavior of High Strength Aluminum Alloys (고강도 알루미늄 합금의 프레팅 피로거동)

  • Choi, Sung-Jong;Lee, Hak-Sun;Lee, Cheol-Jae;Kim, Sang-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.2 s.257
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    • pp.197-204
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    • 2007
  • Fretting is a contact damage process that occurs between two contact surfaces. Fretting fatigue reduces fatigue strength of the material due to low amplitude oscillatory sliding and changes in the contact surfaces of strongly connected machine and structure such as bolt, key, pin, fixed rivet and connected shaft, which have relative slip of repeatedly extreme low frequency amplitude. In this research, the fretting fatigue behavior of 2024-T3511 and 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were experimentally estimated. Based on this experimental wort the following results were obtained: (1) A significant decrease of fatigue lift was observed in the fretting fatigue compared to the plain fatigue. The fatigue limit of 2024-T3511 aluminum alloy decreased about 59% while 7050-T7451 aluminum alloy decreased about 75%. (2) In 7050-T7451 specimen using ATSI4030 contact pad, crack was initiated more early stage than using 2024-T3511 contact pad. (3) In all specimens, oblique cracks were initiated at contact edge. (4) Tire tracks and rubbed scars were observed in the oblique crack region of fracture surface.

Correlation between reverberation time and standing wave (잔향시간과 정재파의 상호관계)

  • 차일환
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.10 no.5
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    • pp.31-38
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    • 1973
  • The Sabine's formula has been widlely used for calculating reverberation time and applied for actual systems. The result of Sabine's method is only same as the reverberation time of one axial wave according to the wave theory. Reverberation time is mainly dependent on the standing waves. In case of the rectangular room the frequencies of three mode covering 250Hz and several intensities at various positions of the room were measures by a spectrograph. It wart found that axial wavers and tangential waves decayed more slowly than oblique waves. The experimental results showed that the amount of axial and tangential wave in a frequency band varies depending on the position in the room. It is concluded that the results give to control reverberation times in a room.

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Effect of Head and Leg Positions on Trunk and Upper Trapezius Muscle Activities during Plank Exercise (플랭크 운동 동안에 머리와 다리 위치가 몸통근육과 위등세모근의 근활성도에 미치는 영향)

  • Kim, Soo-Han;Park, Se-Yeon
    • PNF and Movement
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    • v.17 no.3
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    • pp.401-409
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    • 2019
  • Purpose: This study investigated the muscular activity of abdominal muscles during a variety of plank exercises following changes in the leg and head positions. Methods: Thirty healthy individuals participated in this study. They performed six variations of plank exercises, including three changes in head position and two changes in leg position. Each plank was defined as head neutral-leg neutral, head up-leg neutral, head down-leg neutral, head neutral-leg wide, head up-leg wide, and head down-leg wide. During the plank excises, the muscle activities of the rectus abdominis, internal oblique, erector spinae, and upper trapezius were measured. Results: The head down position significantly increased the rectus abdominis activity compared to other head positions (p<0.05). On the other hand, the upper trapezius muscle activity was significantly higher with the head up position compared to other head positions (p<0.05). Regardless of head positions, both the rectus abdominis and internal oblique muscles were significantly activated with leg wide position compared to the leg neutral position (p<0.05). Conclusion: Head and leg positions could change the muscular activities of abdominal muscles during plank exercises. For example, the head down position is effective for activating the rectus abdominis while the leg wide position could be advantageous for enhancing the internal oblique and rectus abdominis.

Effects of Knee and Foot Position on EMG Activity and Ratio of the Vastus Medialis Oblique and Vastus Lateralis during Squat Exercise (스쿼트 운동시 자세가 안쪽빗넓은근과 가쪽넓은근의 근활성도 및 근활성비에 미치는 효과)

  • Kim, Hyun-Hee;Song, Chang-Ho
    • Journal of muscle and joint health
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    • v.17 no.2
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    • pp.142-150
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    • 2010
  • Purpose: The purpose of this study was to examine EMG activities and VMO/VL ratio of the vastus medialis oblique, vastus lateralis, and rectus femoris during squat exercise (knee angle: 15, 45, and 60 degrees; tibial rotation: internal rotation, neutral, and external rotation). Methods: Twelve subjects performed squat exercise at each knee angle and tibial rotation while electromyographic (EMG) activity was collected. Statistical analysis consisted of two-way repeated measures analysis of variance with post hoc analysis. Results: There were significant main effects of knee angles and foot positions and interaction effect on EMG activities of vastus medialis oblique and vastus lateralis. VMO/VL ratios were significantly different by tibial rotations and there was an interaction effect. A neutral position produced significantly more VMO/VL activity ratio than that from internally rotated position and externally rotated position at 60 degrees. Conclusion: Considering the interaction effects for EMG activity across quadriceps muscles tested, the 60 degrees knee angle with a neutral foot position may provide the most effective condition for patients with acute patellofemoral syndrome.

Electromyographic Analysis of Muscle Activity and Fatigue of the Paraspinal Muscles During a Repetitive Lifting Task (반복 들기 작업에 따른 허리주변 근육의 근활성도와 근피로도에 대한 근전도 분석)

  • Kim, Won-Ho
    • Physical Therapy Korea
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    • v.16 no.3
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    • pp.16-23
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    • 2009
  • The purpose of this study was to investigate the effects of a repetitive lifting task on the level of activation and median frequency of the paraspinal muscles, and to provide basic data of the maximal acceptable duration of the lifting task to avoid muscle fatigue. Ten healthy male subjects were recruited as participants and they repetitively (12 lifts/min) lifted a box ($46cm{\times}30cm{\times}30cm$, 15 kg) for 10 minutes. Electromyographic data (muscle activation and median frequency), heart rate, and Borg CR10 score were recorded at 1, 3, 5, 7, and 9 minutes after the lifting task. Electromyographic data was recorded from the elector spinalis, mutifidus, external oblique abdominis, and rectus abdominis for 1 minute. The results showed that as the repetitive lifting task progressed, the heart rate and Borg CR10 score significantly increased. In addition, activation of the muscles increased. The median frequency significantly decreased over time in the elector spinalis, mutifidus, and external oblique abdominis (right side), except for the external oblique abdominis (left side) and rectus abdominis. It is suggested that the median frequency recorded from a dynamic task is used to monitor muscle fatigue. Furthermore, the repetitive lifting task (15 kg, 12 lifts/min) should not continue for more than 3 minutes in order to avoid muscle fatigue.

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Electro-Optical Characteristic for VA-LCD on the $SiO_x$ Thin Film Layer Oblique Deposited by Sputtering Method (스퍼터링으로 경사증착한 $SiO_x$ 박막을 이용한 VA-LCD의 전기광학특성)

  • Choi, Sung-Ho;Hwang, Jeoung-Yeon;Kim, Sung-Yeon;Oh, Byeong-Yun;Myoung, Jae-Min;Seo, Dae-Shik
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2006.06a
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    • pp.451-452
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    • 2006
  • We studied the electro-optical characteristic of vertical alignment liquid crystal display(VA-LCD) on the $SiO_x$ thin film deposited $45^{\circ}$ oblique by rf magnetic sputtering system. LC alignment characteristic showed homeotropic alignment, and pretilt angle was about $90^{\circ}$. A uniform liquid crystal alignment effect on the $SiO_x$ thin film was achieved and the electro-optical characteristic of the $SiO_x$ thin film deposited $45^{\circ}$ oblique by rf magnetic sputtering system was excellent.

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Oblique Single-Cut Rotation Osteotomy for Correction of Femoral Varus-Torsional Deformities in 3D-Reconstructed Canine Bone Models

  • Kim, Hyeon-Ho;Roh, Yoon-Ho;Lee, Je-Hun;Jeong, Jae-Min;Jeong, Seong Mok;Lee, Hae Beom
    • Journal of Veterinary Clinics
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    • v.37 no.4
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    • pp.180-184
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    • 2020
  • The purpose of this study was to report the reliability and validity of oblique single-cut rotation osteotomy (OSCRO) in 3D-reconstructed canine bone models with femoral varus and torsional deformities. A healthy adult male beagle was recruited to create a 3D bone model, and this bone model was modified by using a 3D program. Fifteen bone models were constructed for this study. OSCRO simulation was performed in accordance with the plan after printing using a 3D printing machine. The anatomical lateral distal femoral angle (aLDFA), anteversion angle (AA), anatomical caudo-distal femoral angle (aCdDFA), mechanical caudo-distal femoral angle (mCdDFA) and pre- and postoperative bone length were calculated. There were no significant differences between the target values and postoperative values. In addition, the difference between pre- and postoperative bone length was small (p = 0.001). Our findings suggest that OSCRO could be an effective surgical option for MPL with bone deformities in small-breed dogs that often undergo conventional distal femoral osteotomy.

An investigation on heat transfer effects of two dimensional plane jet attaching offseted obliqued wall (단이 진 경사벽면에 부착되는 2차원 평면제트의 열전달 효과에 관한 연구)

  • Yun, Sun-Hyeon;Lee, Dae-Hui;Sim, Jae-Gyeong;Song, Heung-Bok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.10
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    • pp.1314-1325
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    • 1997
  • Experiments have been conducted to determine the flow and heat transfer characteristics for a two-dimensional turbulent wall attaching offset jet at different oblique angles to a flat surface. The distributions of the wall static pressure coefficient and time-averaged reattachment position for various offset ratios and oblique angles have been measured. The local Nusselt number distributions on the plate surface were also measured using liquid crystal as a temperature indicator. The new hue-capturing technique utilizing a true color image processing system was used to accurately determine the temperature of the liquid crystal. The experiments were carried out at Reynolds number, Re (based on D) of from 7300 to 21,300 with offset ratio, H/D from 2.5 to 10, and oblique angle, .alpha. from 0 deg. to 400 deg..

Optimal design of homogeneous earth dams by particle swarm optimization incorporating support vector machine approach

  • Mirzaei, Zeinab;Akbarpour, Abolfazl;Khatibinia, Mohsen;Siuki, Abbas Khashei
    • Geomechanics and Engineering
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    • v.9 no.6
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    • pp.709-727
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    • 2015
  • The main aim of this study is to introduce optimal design of homogeneous earth dams with oblique and horizontal drains based on particle swarm optimization (PSO) incorporating weighted least squares support vector machine (WLS-SVM). To achieve this purpose, the upstream and downstream slopes of earth dam, the length of oblique and horizontal drains and angle among the drains are considered as the design variables in the optimization problem of homogeneous earth dams. Furthermore, the seepage through dam body and the weight of dam as objective functions are minimized in the optimization process simultaneously. In the optimization procedure, the stability coefficient of the upstream and downstream slopes and the seepage through dam body as the hydraulic responses of homogeneous earth dam are required. Hence, the hydraulic responses are predicted using WLS-SVM approach. The optimal results of illustrative examples demonstrate the efficiency and computational advantages of PSO with WLS-SVM in the optimal design of homogeneous earth dams with drains.

The Effects of Coordinative Locomotor Training Combined with Climbing on the Trunk Muscles in Adults (20대 남여 대학생에게 클라이밍에서의 협응이동훈련이 몸통근 두께에 미치는 영향)

  • Lim, Jae-Heon;Jang, Hyun-Jin;Cho, Woon-Su;Park, Se-Ju
    • PNF and Movement
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    • v.16 no.3
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    • pp.397-404
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    • 2018
  • Purpose: The purpose of this study was to investigate the effect of climbing training combined with coordinative locomotor training on muscle thickness in normal adults and to provide basic data regarding its applicability to clinical practice. Methods: Coordinative locomotor and climbing training was conducted three times per week for six weeks. Each exercise session consisted of ten minutes of warm-up and 40 minutes of the main exercise. A post-test was conducted six weeks after the training began, and a follow-up test was done two weeks after the training ended. Results: There were significant differences in the participants' external and internal oblique abdominis muscles over time (p<0.05). There were also significant interactions in the external and internal oblique abdominis muscles over time and according to group (p<0.05). Conclusion: The findings indicate that coordinative locomotor training with climbing had positive effects in normal adults, including increased thickness of the external and internal oblique abdominis muscles. The findings hold value for patient rehabilitation and clinical applications and interventions using coordinative locomotor training in combination with climbing.