• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.347-351
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• 2004

[ $Si_3N_4$ ] composites have been extensively studied for engineering ceramics, because it has excellent room and high temperature strength, wear resistance properties, good resistance to oxidation, and good thermal and chemical stability. In the present work, carbon short fiber reinforced $Si_3N_4$ ceramics were fabricated by hot press method in $N_2$ atmosphere at $1800^{\circ}C$ using $Al_2O_3\;and\;Y_2O_3$ as sintering additives. Content of carbon short fiber was $0\%,\;0.1\%\;and\;0.3\%$. The composites were evaluated in terms of density, flexural strength and elastic modulus through the 3-point bending test at room temperature. Also, The wear behavior was determined by the pin on disk wear tester using silicon nitride ball. Experimental density and flexural strength decreased with increasing content of carbon fiber. But specific modulus increased with increasing content of carbon fiber. In addition, friction coefficient and specific wear loss decreased with increasing content of carbon short fiber by reason of interfacial defects between matrix and fiber.

• Journal of Powder Materials
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• v.14 no.6
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• pp.354-361
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• 2007

The bi-materials with Al-Mg alloy and its composites reinforced with SiC and $Al_2O_3$ particles were prepared by conventional powder metallurgy method. The A1-5 wt%Mg and composite mixtures were compacted under $150{\sim}450\;MPa$, and then the mixtures compacted under 400 MPa were sintered at $773{\sim}1173K$ for 5h. The obtained bi-materials with Al-Mg/SiCp composite showed the higher relative density than those with $Al-Mg/Al_2O_3$ composite after compaction and sintering. Based on the results, the bi-materials compacted under 400 MPa and sintered at 873K for 5h were used for mechanical tests. In the composite side of bi-materials, the SiC particles were densely distributed compared to the $Al_2O_3$ particles. The bi-materials with Al-Mg/SiC composite showed the higher micro-hardness than those with $Al-Mg/Al_2O_3$ composite. The mechanical properties were evaluated by the compressive test. The bi-materials revealed almost the same value of 0.2% proof stress with Al-Mg alloy. Their compressive strength was lower than that of Al-Mg alloy. Moreover, impact absorbed energy of bi-materials was smaller than that of composite. However, the bi-materials with Al-Mg/SiCp composite particularly showed almost similar impact absorbed energy to $Al-Mg/Al_2O_3$ composite. From the observation of microstructure, it was deduced that the bi-materials was preferentially fractured through micro-interface between matrix and composite in the vicinity of macro-interface.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.65-69
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• 2010

In this study, we investigated the effects of UBM(Under Bump Metallization) and solder composition on the drop impact reliability of wafer level packaging. Fan-in type WLP chips were prepared with different solder ball composition (Sn3.0Ag0.5Cu, and Sn1.0Ag0.5Cu) and UBM (Cu 10 ${\mu}m$, Cu 5 ${\mu}m$\Ni 3 ${\mu}m$). Drop test was performed up to 200 cycles with 1500G acceleration according to JESD22-B111. Cu\Ni UBM showed better drop performance than Cu UBM, which could be attributed to suppression of IMC formation by Ni diffusion barrier. SAC105 was slightly better than SAC305 in terms of MTTF. Drop failure occurred at board side for Cu UBM and chip side for Cu\Ni UBM, independent of solder composition. Corner and center chip position on the board were found to have the shortest drop lifetime due to stress waves generated from impact.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.11
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• pp.2752-2761
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• 1993

The purpose of this study is to confirm the decreasing problems of residual bending strength, and the fracture machanism experimentally when CFRP composite laminates are subjected to Foreign Object Damage. Composite laminates used for this experiment are CFRP orthotropy laminated plates, which have two-interfaces [O/sub 6//sup o//90/sub 6//sup o/]sub sym/ and four-interfaces [O/sub 3//sup o//90/sub 6//sup o//O/sub 3//sup o]/sub sym/. When the specimen is subjected to transverse impact by a steel ball, the delamination area generated by impact damage is observed by using SAM(Scanning Acoustic Microscope). also, Thefracture surfaces obtained by three-point bending test were observed by using SEM (Scanning Electron Microscope). Then, fracture mechanism was investigated based on the observed delamination area and fracture surface. The results were summarized as follows; (1) It is found that for the specimen with more interface, the critical delamination energy is increased while delamination-development energy is decreased. (2) Residual bending strength of specimen A is greater than that of Specimen B within the impact range of impact energy 1. 65J (impacted-side compression) and 1. 45J (impacted-side tension). On the other hand, when the impact energy is beyond the above ranges, residual bending strength of specimen A is smaller than that of specimen B. (3) In specimen A and B, residual strength of CFRP plates subjected to impact damage is lower in the impacted-side compression than in the impacted-side tension. (4) In the case of impacted-side compression, fracture is propagated from the transverse crack generat-ed near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-B delamination in the case of impacted-side tension.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.41-47
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• 2010

The effect of PCB and BGA pad designs was investigated on the mechanical property of Pb-free solder joints. The mechanical property of solder joint was tested by three different test methods of drop impact tests, bending impact test, and high speed shear test. Two kinds of pad design such as NSMD (Non-Solder Mask Defined) and SMD (Solder Mask Defined) were applied with the OSP finished Pb-free solder (Sn-3.0Ag-0.5Cu, Sn-1.2Ag-0.5Cu). in the drop impact test and bending impact test, the characterized lifetime showed the same tendency, and SMD design showed better mechanical property of solder joint than NSMD regardless of test method, which was due to the different crack path. The fracture crack on SMD pad was propagated along the intermetallic compound (IMC) layer of solder joint, while the fracture crack on NSMD pad propagated through upper edge of land which shields pattern. In the high speed shear test, pad lift occurred on the solder joint of NSMD. SMD/SMD combination of pad design consequently illustrated the best mechanical property of BGA/PCB solder joint, followed by SMD/NSMD, NSMD/SMD, and NSMD/NSMD.

• Journal of the Korean Society of School Health
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• v.5 no.1
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• pp.111-119
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• 1992

The study examined the difference of the physique, the physical strength, and the physical constitution between meal and non-meal service schools at the countryside, and concluded as follows: 1) The effects on the physical development Meal service school student's height was 0.41~2.38cm taller, weight 0.21~1.58kg heavier, and the chests 0.15~2.55cm bigger than the non-meal service school students. Therefore, the effects of the school meal service on the student's physique development proved positive. 2) The effects on the physical strength Today, the student's physical growth is reinforced by consuming high calorie food, while their physical exercise is decreased. As a result, obesity becomes another problem. In this respect, physical strength is a significant factor in judging the physical condition of the students. This study compared the meal service schools with the non-meal service schools by suing six items of the physical strength test those schools. In comparison, the meal service school students were better than the others in most items except in the eleven year old girl's 100 meter running and the ball throwing, and the ten year old boy's 600meter running. It means that school meal service affects the physical growth in a positive manner. 3) The effects on the physical constitution The students in their growing period should have their meals not only balanced, but regularly since this helps to maintain their health. Insufficient nutrition may disturb the balanced physical growth of cause a weak or powerless physical constitution. As shown at the table 6, meal service school students who had a balanced meal have 0.01% lower incidence of disease. and 3.11~7.32% less myophia than the other. The average 0.39 to 0.63 cavity of the meal service school students also show that their constitutions are better than the non-meal service ones. In conclusion, the school meal service program gives every student a regular nutritious meal which results in a balanced physical growth. Erentually, the healthier students could be the healthier social menbers which promise a brighter society in the future.

• Journal of The Korean Society of Integrative Medicine
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• v.3 no.4
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• pp.37-42
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• 2015

Purpose: This study was conducted to test the impact of The Dynamic Visual-Motor integration training has effect on the visual perception reaction velocity. Dynavision were used to measure data from the participating 24 students(K college). Method : The participants were the 24 students of 'K' College in Busan in there twenties. They were divided into the The Dynamic Visual-Motor integration training group and the control group. To know if the Dynamic Visual-Motor integration training has effect on the visual perception reaction velocity, the Dynamic Visual-Motor integration training was implemented triweekly for 4 weeks. In Dynamic Visual-Motor integration training the ball should be grasped with one hand and threw by an arm. Only the balls threw beyond the objective point were counted. The visual perception reaction velocity and the number of response were measured before and after experiment by Dynavision. Result : Firstly, the visual perception reaction velocity was increased in Dynamic Visual-Motor integration training group compared with control group. Secondly, the number of response was also increased in Dynamic Visual-Motor integration training group compared with control group. Conclusion : As a result of The Dynamic Visual-Motor integration training has an effect on the visual perception reaction velocity and the number of response. The Dynamic Visual-Motor integration training seems to be effective for cerebral apoplexy patient who has visual perceptional disability or cerebral palsy child in training for visual perceptional development or daily living activities development. Study participated by more detailed and practical patients in hospital is needed.

• KCI Concrete Journal
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• v.13 no.2
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• pp.10-18
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• 2001

The spectral analysis of surface waves (SASW) method, which is an in-situ seismic technique, has mainly been developed and used for many years to determine the stiffness profile of layered media (such as asphalt concrete and layered soils) in an infinite half-space. This paper presents a modified experimental technique for nondestructive evaluation of in-place cement mortar compressive strength in single-layer concrete slabs of rather a finite thickness through a correlation to surface wave velocity. This correlation can be used in the quality control of early age cement mortar structures and in evaluating the integrity of structural members where the infinite half space condition is not met. In the proposed SASW field test, the surface of the structural members is subjected to an impact, using a 12 mm steel ball, to generate surface wave energy at various frequencies. Two accelerometer receivers detect the energy transmitted through the medium. By digitizing the analog receiver outputs, and recording the signals for spectral analysis, surface wave velocities can be identified. Modifications to the SASW method includes the reduction of boundary reflections as adopted on the surface waves before the point where the reflected compression waves reach the receivers. In this study, the correlation between the surface wave velocity and the compressive strength of cement mortar is developed using one 36"x36"x4"(91.44$\times$91.44$\times$91.44 cm) cement mortar slab of 2,000 psi (140 kgf/$\textrm{cm}^2$) and two 36"x36"x4"(91.44$\times$91.44$\times$91.44 cm) cement mortar slabs of 3,000 psi (210 kgf/$\textrm{cm}^2$).

• Tribology and Lubricants
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• v.31 no.4
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• pp.183-188
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• 2015

This paper presents the experimental effects of lubricant with nanodiamond particles in sliding friction. In order to improve the performance of lubricants many additives are used, such as MoS₂, cadmium chloride, indium, sulfides, and phosphides. These additives are harmful to human health and to the environment, so alternatives are necessary. One such alternative is nanodiamond powder, which has a large surface area. In order to investigate the effect of nanodiamonds in lubricants under sliding friction, they are dispersed in the lubricant at a variety of concentrations (0 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1 wt%) using the matrix synthesis method. Friction and wear tests are performed according to the ASTM G99 method using a pin-on-disc tester at room temperature. The specimens used in this experiment are AISI 52100 ball bearings and AISI 1020 steel discs. During the test, lubricant mixed with nanodiamond is supplied constantly to keep the two bodies separated by a lubricant film. To maintain boundary lubrication, the speed is set to 0.18 m/s and a load of 294 N is applied to the disc through the pin. Results are recorded by using workbench software over the test duration of 10 minutes. Experimental results show that when the concentration of nanodiamond increases, the coefficient of friction decreases. However, above a nanodiamond concentration of 0.5 wt%, both the coefficient of friction and wear volume increase. From this experiment, the optimum concentration of nanodiamond showing a minimum coefficient of friction of 0.09 and minimum wear volume of 0.82 nm² was 0.5 wt%.

• Journal of Korean Physical Therapy Science
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• v.24 no.1
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• pp.1-13
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• 2017

Purpose: The objective of this study was compare the effect of core muscle strengthening between core exercise on stable surface and core exercise on unstable surface. Methods: Thirty-nine adults participated in this study and were randomly allocated to three groups. The stable surface exercise group and unstable surface exercise groups practiced core muscle training for $3{\times}30minute$ sessions over a 4-week period. The control group did not received therapeutic intervention except pre and post test. The following clinical tools were used to assess core muscle strength and balance: Side Plank Test, Trunk Flexion Test, Balance Error Scoring Test, Core Muscle Stength & Stability Test. Results: The stable surface exercise group showed significant improvement in trunk muscle strength of anterolateral part as revealed by the Side Plank Test and Trunk flexion Test(p<.05). The unstable surface exercise group showed significant improvement in trunk muscle strength of anterolateral part and balance ability as revealed by the Balance Error Scoring Test and Core Muscle Strength & Stability Test(p<.05). Conclusion: The results of this study, both core exercise on stable surface and core exercise on unstable surface induced core muscle strengthening and balance ability. Expecially core exercise on unstable surface more effective to core muscle strengthening and balance ability.