• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1013-1019
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• 2016

CFRP is the composite material manufactured by the hybrid resin on the basis of carbon fiber. As this material has the high specific strength and the light weight, it has been widely used at various fields. Particularly, the unidirectional carbon fiber can be applied with the layer angle. CFRP made with layer angle has the strength higher than with no layer angle. In this paper, the property of crack growth due to each layer angle was investigated on the crack propagation and fracture behavior of the CFRP compact tension specimen due to the change of layer angle. The value of maximum stress is shown to be decreased and the crack propagation is slowed down as the layer angle is increased. But the limit according to the layer angle is shown as the stress is increased again from the base point of the layer angle of $60^{\circ}$. This study result is thought to be utilized with the data which verify the probability of fatigue fracture when the defect inside the structure at using CFRP of mechanical structure happens.

• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.115-126
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• 2017

This paper proposes an accelerated life evaluation of drive shaft for the power train parts of special purpose vehicle. It is necessary the real load data of usage level driving load condition for life evaluation of power train parts, but we can't get the load spectrum data for evaluation in many case of special purpose vehicle. So, in this paper, the road load spectrum data for evaluation is created by modeling and simulation based on vehicle data and special road condition. The inverse power model is used for accelerated life test. The equivalent torque of load spectrum is achieved using the Miner's Rule. This paper also proposes the calibrated acceleration life test method for drive shaft. The fatigue test is performed through three stress levels. The lifetime at normal stress level is predicted by extrapolation, and is verified through comparison of experimental results and load spectrum data.

• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.89-95
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• 2017

LCD robot vertical frame lets a arm assembly with glass substrate move up and down, so it must have high stiffness and strength. We applied new manufacturing process by using design optimization process such as topology and size optimization in order to satisfy the request of high stiffness and light weight. The proposed model should be evaluated for endurance strength. Therefore fatigue assessment for weak point of aluminum welding area of vertical frame studied with hot spot stress approach. And the actual stress measuring from test was compared and evaluated with the dynamic stress calculated from multi-body dynamics considering flexible body.

• Archives of design research
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• v.15 no.3
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• pp.241-248
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• 2002

Researches of Hangul automation have been focused mainly on the set of character system. But, practical problem of using the Korean standard keyboard system of two sets is increment of errors and fatigue due to frequent use of shift keys. The author formulate a hypothesis as follows to solve the problem. 'Changing location and design of shift keys can reduce errors in typing Korean by avoiding interferences with other keys when pressing shift keys.' This study verify the hypothesis by the analysis of experiments using improved keyboard prototypes which have changed layout and design of shift keys. On the result, change of shift key location causes confusion to experienced user. But, while keeping its location, removing other keys at the bottom row and magnifying size of shift keys decrease errors in typing by avoiding interferences. And, the efficiency of typing in Korean is increased, too, because there is not any influence on typing speed. This study focuses on layout and design of shift keys only, but further study for entire layout of keyboard including alternative location of other function keys is needed to improve general usability.

• Steel and Composite Structures
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• v.25 no.1
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• pp.79-92
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• 2017

Initial damage to a stud due to corrosion, fatigue, unexpected overloading, a weld defect or other factors could degrade the shear capacity of the stud. Based on typical push-out tests, a FEM model and theoretical formulations were proposed in this study. Six specimens with the same geometric dimensions were tested to investigate the effect of the damage degree and location on the static behavior and shear capacity of stud shear connectors. The test results indicated that a reduction of up to 36.6% and 62.9% of the section area of the shank could result in a dropping rate of 7.9% and 57.2%, respectively, compared to the standard specimen shear capacity. Numerical analysis was performed to simulate the push-out test and validated against test results. A parametrical study was performed to further investigate the damage degree and location on the shear capacity of studs based on the proposed numerical model. It was demonstrated that the shear capacity was not sensitive to the damage degree when the damage section was located at 0.5d, where d is the shank diameter, from the stud root, even if the stud had a significant reduction in area. Finally, a theoretical formula with a reduction factor K was proposed to consider the reduction of the shear capacity due to the presence of initial damage. Calculating K was accomplished in two ways: a linear relationship and a square relationship with the damage degree corresponding to the shear capacity dominated by the section area and the nominal diameter of the damaged stud. This coefficient was applied using Eurocode 4, AASHTO LRFD (2014) and GB50017-2003 (2003) and compared with the test results found in the literature. It was found that the proposed method produced good predictions of the shear capacity of stud shear connectors with initial damage.

• Journal of Korean Medicine Rehabilitation
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• v.20 no.3
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• pp.37-60
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• 2010

Objectives : The purpose of this study was to investigate the relationship between masseter and cervical muscle activity and temporomandibular disorder in female office workers. Methods : Experimental group of 24 healthy subjects complained of temporomandibular joint related to computer use which lasted more than 3 months in the past year and was present in the past 7 days as well as on the day of test. Control group of 20 healthy subjects had no complaints of minimal discomfort on the day of test, and had no discomfort in the past 7 days. If they had reported discomfort in the past 12 months, it was of a short duration(<3 months) and resolved at least 3 months prior to participation. Outcomes were assessed by meridian-electromyography(MEMG), whole spin x-ray, mandibular function impairment questionnaire(MFIQ), neck disability index(NDI), visual analog scale(VAS), Beck depression inventory(BDI), stress reaction inventory(SRI) and Holmes & Rahe social readjustment rating scale(SRRS). Results : The contraction power of masseter muscle, upper trapezius, sternocleido-mastoid muscle and erector spinae by MEMG was significantly higher in the experimental group. The muscle fatigue of masseter muscle and sternodeido-mastoid muscle by MEMG was significantly higher in the experimental group. SRI was significantly higher in experimental group. There was no significant difference between two groups in the Jackson's angle, Cobb's method and cranio-cervical posture. Conclusions : The results suggest that temporomandibular disorder related mental stress but physical stress does not change cervical structure significantly.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.2
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• pp.13-21
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• 1999

Flip chip assembly directly on organic boards offers miniaturization of package size as well as reduction in interconnection distances resulting in a high performance and cost-competitive Packaging method. This paper describes the investigation of alternative low cost flip-chip mounting processes using electroless Ni/Au bump and anisotropic conductive adhesives/films as an interconnection material on organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au plating was performed and characterized in mechanical and metallurgical point of view. Effect of annealing on Ni bump characteristics informed that the formation of crystalline nickel with $Ni_3$P precipitation above $300^{\circ}C$ causes an increase of hardness and an increase of the intrinsic stress resulting in a reliability limitation. As an interconnection material, modified ACFs composed of nickel conductive fillers for electrical conductor and non-conductive inorganic fillers for modification of film properties such as coefficient of thermal expansion(CTE) and tensile strength were formulated for improved electrical and mechanical properties of ACF interconnection. The thermal fatigue life of ACA/F flip chip on organic board limited by the thermal expansion mismatch between the chip and the board could be increased by a modified ACA/F. Three ACF materials with different CTE values were prepared and bonded between Si chip and FR-4 board for the thermal strain measurement using moire interferometry. The thermal strain of ACF interconnection layer induced by temperature excursion of $80^{\circ}C$ was decreased with decreasing CTEs of ACF materials.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.3
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• pp.25-29
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• 2009

High temperature high humidity and thermal shock reliability tests were performed for the board level COB(chip-on-board) flip chip packages using self-formulated and commercial NCPs(non-conductive pastes) to ensure the performance of NCP flip chip packages. It was considered that the more smaller fused silica filler in prototype NCPs is more favorable for high temperature high humidity reliability. The failure of NCP interconnection was affected by the expansion of epoxy due to moisture absorption rather than the fatigue due to thermal stress. It was considered that the NCP having more higher adhesive strength seems to be more favorable to increase the thermal shock reliability.

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.88-94
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• 2013

The purpose of this study is to find out the difference of foot pressure according to the firefighter's work postures for providing the basic information to prevent Musculoskeletal disorders. This study was conducted by 9 male firefighters. Work postures were selected for rescuee handling, fire hose and hydraulic rescue equipment work postures. These were divided into 3 position, "High", "Middle" and the postures of taking out and letting down hydraulic rescue equipment were analyzed as starting point and end point respectively. Foot Pressure was used to analyze contact area, peak pressure, and maximum force in terms of work postures, and compared between fire hose and hydraulic rescue equipment work postures. The results of foot pressure are as follows. According to the results of rescuee handling work postures, one person handling posture showed wide contact area and foot pressure showed the highest at right foot. Accoridng to the (High), (Middle), (Low) postures of fire hose, the results didn't show the difference among the contact area, peak pressure and maximum force. As the results of hydraulic rescue equipment work postures, (Low) postures showed the highest in terms of the right foot of contact area, peak pressure and maximum force and (High) postures showed the highest in left foot. The increase of foot pressure lead to be inconvenience of low extremity and muscle fatigue for maintaining postural control cause pain. Thus, it is necessary to design insole-equipped working shoe for reduce the impulse and effect of foot during the rescuee handling work which standing out as foot pressure.

• Korean Journal of Oriental Medicine
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• v.16 no.1
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• pp.149-155
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• 2010

Objective : Ssangwha-tang is a traditional medicine formula widely prescribed for a decrease of fatigue after an illness in Korea. The aim of this study is to investigate the effect of Ssangwha-tang fermented by Lactobacillus fermentum (SF) on osteoclast differentiation in vitro and on bone metabolism of an ovariectomized rat in vivo. Methods : Tartrate-resistant acid phosphatase activity and staining were applied to evaluate the formation of osteoclasts. Ovariectomized rats were orally administrated with SF (30 ml/kg/day) for 12 weeks. Serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total cholesterol, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, triglyceride, phosphate, calcium levels were determined. Effect of SF on bone loss were studied by histological analysis and the measurement of bone mineral density. Results : SF significantly inhibited tartrate-resistant acid phosphatase activity and formation of osteoclasts in RAW264.7 cells stimulated by receptor activator for nuclear factor ${\kappa}B$ (NF-${\kappa}B$) ligand (RANKL). In addition, SF significantly decreased the level of triglyceride and increased the level of low-density lipoprotein. Moreover, the decrease of trabeculae of the femur was partially prevented in ovariectomized rats administrated with SF. Conclusions : SF treatment could prevent ovariectomy induced bone loss and its effects could be medicated by the inhibition of osteoclastogenesis.