• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.330-336
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• 2000

Effects of microstructure and indentation stress on fracture behavior of glass-infiltrated alumina composite for dental restorative application were investigated by the Hertzian and Vickers indentation method. Indentation stress-strain curve of glass-infiltrated alumina has showed the quasi-plastic behavior - deviation from linearity at high stress and the classical Hertzian cone crack, which could be confirmed the subsurface damage micrographs using bonded-interface specimen technique. The indentation stress-strain curves for the starting preforms are strongly dependent on porosity and microstructure of the preforms. On the other hand, the curves for the infiltrated composites are relatively insensitive to these factors. The failure of composite is originated at quasi-plastic deformation region. Damage and fracture behavior due to Hertzian stress field is theoretically examined, so that the indentation stress field plays a great role in material degradation. After Hertzian indentation annealing processing changes fracture behavior of alumina composite, so that stress field in material is healed through annealing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.2
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• pp.103-108
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• 2007

A stress measurement method of structural member using piezoelectric property and electrostatic voltmeter is presented. The electric potentials of the surface of the piezoelectric element, which are proportional to the strain ${\varepsilon}$ on the structural member, are measured by an electrostatic voltmeter during load cycling. The stress ${\sigma}$ is calculated by this strain ${\varepsilon}$. Moreover, a stress distribution measurement tape which can be used for the stress distribution measurement along a specified line on the surface of structural member is developed, and the surface potential was measured by an electric static voltmeter of non-contact type. The applicability of the stress distribution measurement tape is examined through experiments using a notched specimen under cyclic loading. The measured distributions of x, y and xy are compared with those calculated by FEM analysis.

• Computational Structural Engineering
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• v.11 no.1
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• pp.80-89
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• 1998

본 기사에서는 기존 구조물의 구조를 변경하여 사용하는 경우 구조물 축소모형시험과 수치해석을 이용하여 안전도를 합리적으로 평가하는 절차에 관하여 지하철 정차장 구조물을 예로하여 살펴보았다. 구조물의 안전도를 평가하기 위한 구조물 축소모형 시험에서는 원형구조물의 실제 거동을 나타내는 모형의 제작이 가장 중요한 사항이다. 이를 위해서 적절한 상사율을 가지는 구조재료의 선정, 합리적인 경계조건의 설정, 실제하중을 고려한 재하방법 등을 결정하여야 한다. 구조재료의 선정과 모형의 축소율은 모형구조의 거동이 탄성범위 내인가 또는 극한거동인가에 따라 결정되는 것이 일반적이다. 안전도 평가를 위한 모형구조물의 제작과정에서는 원형구조물 거동을 수치해석을 통하여 예측하는 과정이 필요하며 이러한 사전해석(pre-analysis)을 통하여 구조물의 개략적인 거동과 측정항목을 정하며, 또한 합리적인 재하방법을 결정하게 된다. 모형구조물에 대한 재하시험을 통하여 원형구조물의 거동을 상사비를 적용하여 바로 예측할 수 있으나 재하하시험후 측정된 사항에 대하여는 모형구조물에 대한 사후해석(post-analysis)를 수행하여 측정값과 비교 검토하여 거동의 일치성을 입증하는 것이 일반적이다. 이런 과정을 거쳐 검증된 수치해석모델을 이용하여 실험에서 고려하지 않은 여러가지 하중조건에 수치적으로 검토할 수 있으며, 이를 이용하여 안전도검토와 적절한 대책을 수립할 수 있게 된다. 사전해석-모형시험-사후해석의 절차에 따른 구조물의 모형실험의 사례는 미국과 유럽에서 찾아볼 수 있으며 이를 통하여 수치해석기법의 발전이 이루어지고 있다. 현재까지 우리나라에서는 구조물 모형실험에 관련된 연구가 활발하지 못한 편이며, 상대적으로 경험이 적게 축적되어 있는 실정이다. 그러나 수치해석기법의 발전과 실제구조물의 안전도를 합리적으로 파악하기 위해서는 구조물모형 실험이 필수적이며 앞으로 연구가 활발히 이루어져야 할 분야로 사료된다.leic acid와 palmitic acid가 주요 지방산이었으나 싸리버섯은 중성지질에서 oleic acid의 함량이 높았다.n the part of special landscape management area, it is necessary to introduce landscape impact assessment system to more effective landscape management.ch served as supporting organizations. The control of the construction and management of the royal garden and landscape was held by decision makers, executors of works and management. 2) The general process of the construction and management of the royal garden and landscape included Sangji and Kyuho다 as the first step; In case of buildings and facilities, according to former examples and drawings, the most of the planning and design was already fixed. In the case of landscape, those things aimed at construction according to the existing lie of the land. The works in the 2nd step; This process was divided into the construction of facilities and planting. In case of construction of facilities, those works were done by Togam and

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.56-56
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• 2017

점적 호스 중 PC 드립은 경질 호스의 내부에 Micro-path가 부착된 유로장치와 압력을 보상하는 연질의 실리콘으로 구성되어 있다. 이때 일정압력에서 적정 길이까지 동시에 내부 압력을 유지하며 균등하게 유출구를 통하여 유량을 공급하는 압력보상 기능이 매우 중요하다. 그러나 이 부분에 대한 기술은 선진국에 비해 아직 부족하여 수입에 의존하는 경향이 매우 높다. 뿐만 아니라 선진국 제품에 비해 유로장치 및 연질 실리콘의 탄성이 균일하지 못해 압력에 따른 유량의 편차가 큰 편이다. 본 연구에서는 우리나라 제품의 PC 드립 압력 균등성 기술을 향상시키기 위해 PC 드립의 핵심기술인 연질 실리콘의 성능에 대한 평가와 유량의 편차를 분석하여 문제점을 통한 개선방안을 제시하고자 하였다. 연질 실리콘의 규격은 $17{\times}8{\times}0.85mm$ (가로${\times}$세로${\times}$두께)로서 Water line의 내부에 결합되어 구성된다. PC 드립용 실리콘은 국내 A사 제품을 중심으로 하여 성능을 측정하였다. 측정을 정밀하게 하기 위해 Microtester를 사용하여 일정하게 하중이 부과되도록 하였다. 연질의 실리콘의 경도는 압력 보상에 중요한 기능을 하고 있으며 또한 PC 드립의 경질 미로와 같이 압력을 제어하는 역할을 하고 있다. 국내 A사의 실리콘 경도는 이상적인 실리콘 경도에 비하면 매우 불균일하였다. 세부적으로는 40 이하의 낮은 경도에서는 비교적 일치하였으나 경도 45 이상에서는 큰 차이를 보여주고 있었다. 국내 A사의 실리콘 경도에 따른 공급유량의 특성에서는 실리콘의 경도가 낮을수록 실리콘은 무르며 탄성이 줄어든다. 반면에 경도가 높을수록 탄성이 커지고 딱딱한 특성을 가진다. 동일한 PC 드립에 실리콘의 경도별 특성은 경도에 따른 유량이 반드시 일정하지 않으며 대체로 경도가 높을수록 동일 압력에 대해 유량이 많아지는 것을 알 수 있었다. 압력의 변화에 대해 유량이 일정하게 유지하는 특성을 가질수록 사용범위가 넓어지고 안정성이 높은 것으로 판단되며 실리콘 경도 35~55 범위에서 1~2bar의 공급압력에서 사용하는 것이 적합할 것으로 보여진다. 경도 45의 실리콘을 사용하여 수입 드립, 국내 A사의 드립 및 수입과 국내 혼용시 압력에 따른 공급유량의 특성을 분석하였다. 최대 유량과 최소 유량에서 발생되는 오차는 수입 실리콘이 비교적 작았으나 3.6 bar 이상에서는 유량이 급격히 떨어지는 양상을 보였다. 국내 A사의 제품은 0.8~2.0 bar 까지 성능이 비슷했으나 0.8 bar 이하에서는 오차가 있었으나 높은 압력에서는 오히려 성능이 우수하였다. 수입 드립과 다소 유사한 성능을 나타낸 것이 A사 드립과 수입 실리콘을 혼용하여 사용한 것은 전체적으로 비슷한 양상을 나타내었다. 따라서 실리콘 경도 오차를 고려하면 압력별 유량의 변화는 실리콘의 경도와 밀접한 관계가 있는 것으로 판단되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.481-492
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• 2018

The steel-plate concrete composite beam is composed of a steel plate, concrete and shear connector to combine two inhomogeneous materials. In general, the steel plate is assembled by welding an existing composite beam. In this study, the SPC beam was composed of folding steel plates and concrete, without a headed stud. The folding steel plate was assembled by a high strength bolt instead of welding. To improve the workability in a field construction, a hat-shaped cap was attached to the junction with a slab. Monotonic load testing under two points was conducted under displacement control mode to analyze the flexural strength of the SPC beam using a cap as the shear connector. Five specimens with shear connector types, protrusion length, and different thickness of steel plates were constructed and tested. The experimental results were analyzed through the relationship between the shear strength ratio and flexural strength in KBC 2009. The test results showed a shear strength ratio of more than 40 %. In the case of using a cap-like specimen as the shear connector, the flexural strength was 70% of the value calculated as a fully composite beam. In addition, the cap showed a smaller shear strength than the stud, but the cap served as a shear connection. When the thickness of the steel plate was taken as a variable, the steel plate exhibited a bending strength of approximately 70% compared to a fully formed steel plate, and exhibited similar deformation performance. Local buckling occurred due to incomplete composite behavior, but local buckling occurred at a 5% higher strength for a relatively thick steel plate. The buckling width also decreased by 15%.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.212-219
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• 2003

This study is to evaluate the characteristics of SCC at the welded region of high strength steel using acoustic emission(AE) method. Specimens were loaded by a slow strain rate method in synthetic seawater and the damage process was monitored simultaneously by AE method. Corrosive environment was controlled using the potentiostat, in which -0.8V and -1.1V were applied to the specimens. In the case of one-pass weldment subjected to -0.8V, much more AE counts were detected compared with the PWHT specimen. It was verified through the cumulative counts that coalescence of micro cracks and cracks for the one pass weldment with -0.8V were mostly detected. In case of the one pass weldment subjected to -1.1V, time to failure became shorter and AE counts were produced considerably as compared with that of the two pass weldment. It was shown that AE counts and range of AE amplitude have close relations with the number and size as well as width of the cracks which were formed during the SCC.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.2
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• pp.137-147
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• 2008

Statement of problem: Dental implant procedure has been recognized as a very effective treatment to rehabilitate fully or partially edentulous patients. However, mechanical failures such as screw loosening, screw fracture have been still reported frequently. Purpose: The purpose of this study was to evaluate the influence of tungsten carbide/carbon coating, which has superior hardness and frictional wear resistance, on implant-abutment screw loosening of three different joint connections after one million cyclic loading. Material and methods: The values of detorque before and after loading were measured in three different joint connections (Osstem Implant, Korea), one external butt joint, US II implant system and two internal cones, SS II and GS II system. The values of detorque before loading was analyzed by one-way ANOVA, and two-way ANOVA and Scheffe' test were performed for the value of detorque after loading. Results: 1. The values of initial detorque of tungsten carbide/carbon coated Ti alloy screw were smaller those of Ti alloy screw (P<.01), and there were no differences among implant systems in each screw (P>.05). 2. In comparison of loss rate of detorque value after cyclic loading, US II system was greater than SS II and GS II system but there was no difference between SS II and GS II system (P<.01). 3. Loss rates of detorque value after cyclic loading decreased consistently at tungsten carbide/carbon coated Ti alloy screw comparing with Ti alloy screw in all implant systems (P<.01), and there were no differences among three systems in reduction of loss rates by using tungsten carbide/carbon coated Ti alloy screw (P>.05). Conclusion: Tungsten carbide/carbon coating to increase preload with reduction of friction resistance was a effective way to decrease screw loosening by functional loading.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.913-920
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• 2011

We describe the evaluation of the fatigue life and strength of a lightweight railway bogie frame made of glass fiber/epoxy 4-harness satin-woven composites. To obtain the S-N curve for the evaluation of the fatigue characteristics of the composite bogie frame, we performed a tension-compression fatigue test for composite specimens with different stacking sequences of the warp direction, fill direction, and $0^{\circ}/90^^{\circ}$ direction. We used a stress ratio (R) of -1, a frequency of 5 Hz, and an endurance limit of $10^7$. The fatigue strength of the composite bogie frame was evaluated by a Goodman diagram according to JIS E 4207. The results show that the fatigue life and strength of the lightweight composite bogie satisfy the requirements of JIS E 4207. Given its weight, its performance was better than that of a conventional metal bogie frame based on an SM490A steel material.

• Composites Research
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• v.22 no.5
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• pp.15-23
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• 2009

The lubricant tribological characteristics of $Al_2O_3$ fiber and SiC particle hybrid metal matrix composites (MMCs) fabricated by squeeze casting method was investigated using a pin-on-disk wear tester. The wear tests of the MMCs were performed according to fiber/particle hybrid ratio in the planar-random (PR) and normal (N) orientations sliding against a counter steel disk at a fixed speed and $25\;kg_f$ loading under different sliding distances and temperatures. The test results showed that the wear behavior of MMCs varied with fiber orientation and hybrid ratio. At room temperature, the lubricant wear behavior of F20P0 unhybrid PR-MMCs was superior to that of N-MMCs while the hybrid composites exhibited the reverse lubricant wear behavior. It was also revealed that the wear resistance of PR-MMCs was superior to that of the N-MMCs due to the joint action of reinforcements and lubricant film between the friction surfaces at an elevated temperature of $100^{\circ}C$ for both fiber only and hybrid cases. In case of $150^{\circ}C$, although the trend of weight loss was similar to that of others, the wear resistance of PR-MMCs was better than that of N-MMCs for hybrid MMCs.

• The korean journal of orthodontics
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• v.33 no.4 s.99
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• pp.307-317
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• 2003

Conventional osseointegrated titanium implants have many limitations; large size, limited location for placement of the implant, severity of the surgery, discomfort of initial healing, difficulty of oral hygiene and uncontrollable force direction. Recently titanium miniscrew and miniplate have been used for an alternative to conventional dental implant. But in relation to miniplate, miniscrew has disadvantages in that more potential inflammation, light orthodontic force application and limited orthodontic application. This study was conducted to evaluate the effectiveness of miniplate by observing the reactions of peri-implant tissues to early orthodontic and orthopedic loading of titanium miniplate. In four adult beagle dogs 10 miniplates were inserted into the alveolar bone using 20 osseointegrated titanium screws. 4 miniplates were placed in two dogs(dogA, B) and 6 miniplates in two dogs(dogC, D). In dogA, B miniplates were loaded with 200gm of force immediately after placement for 15 weeks. In dogc, D, miniplates were loaded with 400gm of force immediately after placement for 8 weeks. Miniplates of dogA were removed, dogA was healed for 4 weeks, and the area which was removed of miniscrew was examined. Following an observation period, the miniplates including miniscrews and the surrounding bone of dogB and dogC, D were removed, respectively. Undecalcified section along the long axis of miniscrews were made and the degree of osseointegration was examined under the light microscope. The results were as follows. 1. In the histologic features there was direct contact between bone and miniscrew in all groups except one, dogC control group. The loaded miniscrew demonstrated only a slight increase of the osseous proximaty when compared with unloaded miniscrew 2. There was no significant difference of the osseointegration of Peri-miniscrew surface between dogB and dogC, D. But dogB showed slightly more increased bone apposition than dogC, D 3. The gingiva overlapping the miniplate and miniscrew showed no inflammatory sign in clinical and histological aspects. 4. The impaled hard and soft tissues at the area which was removed of miniscrews showed good healing without inflammatory reaction. 5. The mobility showed slight increase in un-loaded miniplate but that was insignificant. Based on the results of this study, miniplate(C-tube) can be used as a firm osseous orthodontic and orthopedic anchorage unit immediately after insertion.