• Composites Research
• /
• 제20권3호
• /
• pp.50-54
• /
• 2007

본 연구에서는 IPMC의 기본적인 기계적 특성을 알아보았다. 기전폴리머의 한 종류인 IPMC는 굽힘형 작동, 가벼움, 저전력 소모, 유연성 등의 많은 장점을 가진 재료이다. 따라서 IPMC는 생체모방형 작동기와 센서로서 많은 가능성을 가지고 있다. 이런 가능성을 바탕으로 IPMC를 실제로 응용하기 위하여 IPMC의 변형, 구동력, 주파수 응답 등 기본적인 기계적 특성을 연구하였다. 우선 이온교환폴리머의 한 종류인 네피온 용액을 사용하여 여러 가지 두께의 네피온 막을 만들고, 무전해 도금을 통해 IPMC를 제작하였다. 이렇게 제작된 IPMC의 규격, 인가 전압에 따른 변형, 구동력, 주파수 응답 특성에 관한 실험을 수행하고, 실험 결과를 통해 IPMC 성능의 실험식과 등가 강성 모델을 수립하였다.

• The Journal of Advanced Prosthodontics
• /
• 제15권3호
• /
• pp.145-154
• /
• 2023

PURPOSE. The objective of this study was to investigate how internal structures influence the overall and marginal accuracy of full arch preparations fabricated through additive manufacturing in different printing systems. MATERIALS AND METHODS. A full-arch preparation digital model was set up with three internal designs, including solid, hollow, and grid. These were printed using three different resin printers with nine models in each group. After scanning, each data was imported into the 3D data processing software together with the master cast, aligned and trimmed, and then put into the 3D data analysis software again to compare the overall and marginal deviation whose results are expressed using root mean square values and color maps. To evaluate the trueness of the resin model, the test data and reference data were compared, and the precision was evaluated by comparing the test data sets. Color maps were observed for qualitative analysis. Data were statistically analyzed by one-way analysis of variance and Bonferroni method was used for post hoc comparison (α = .05). RESULTS. The influence of different internal structures on the accuracy of 3D printed resin models varied significantly (P < .05). Solid and grid models showed better accuracy, while the hollow model exhibited poor accuracy. The color maps show that the resin models have a tendency to shrink inwards. CONCLUSION. The internal structure design influences the accuracy of the 3D printing model, and the effect varies in different printing systems. Irrespective of the kind of printing system, the printing accuracy of hollow model was observed to be worse than those of solid and grid models.

• 대한토목학회논문집
• /
• 제28권5A호
• /
• pp.747-756
• /
• 2008

본 논문에서는 전달길이에 영향을 미치는 인자에 따라 프리텐션 부재가 받는 동적 충격에 의한 영향을 실험적으로 고찰하였다. 이를 위해 긴장재의 직경, 콘크리트의 피복 두께, 구속 철근과 비부착 구간의 유무, 긴장력 도입 방식을 변수로 한 10개의 프리텐션 콘크리트 부재를 제작하고, 긴장재에 부착한 전기 저항식 변형률 게이지를 통하여 부재에 긴장력 도입 시 변형률 변화를 동적으로 측정하였다. 실험 결과, 순간 전달 방식으로 긴장력을 도입할 때 절단단부에서 큰 동적 효과가 발생하는 것을 확인할 수 있었다. 또한, 변형률 변화량으로 각 부재의 긴장력을 비교한 결과, 각 인자에 따라 차이가 존재하는 것을 확인했다. 직경 15.2 mm 강선보다 12.7 mm 강선의 잔류 긴장력 비율이 더 컸으며, 75 mm의 콘크리트 피복 두께만으로도 충분한 구속 효과를 기대할 수 있는 것으로 판단된다. 구속 철근의 영향은 미미했고, 비부착 구간의 영향으로 잔류 긴장력이 향상되었다. 순간 전달 방식보다 지연 전달 방식으로 긴장력을 도입할 때 긴장력 손실이 적은 것으로 확인되었다.

• 한국임상수의학회지
• /
• 제40권3호
• /
• pp.215-220
• /
• 2023

A 3-month-old Korean native cattle (Hanwoo) calf with difficulty taking normal posture and an inability to rise was referred for a definite diagnosis and active treatment, including surgery. The calf had a history of an accident in which both hind limbs were trapped in a barn structure. After admission, a "rabbit leg" posture was observed, a typical sign of gastrocnemius muscle rupture, and both digits were knuckled downward like they were trying to grip the ground. This was considered to be a result of the superficial digital flexor not rupturing but only the gastrocnemius muscle rupturing. Physical examination revealed laceration of the metatarsus and firmness behind both stifle joints which were presumed to be the sites of gastrocnemius muscle rupture. Skeletal abnormalities, including fractures, were ruled out by radiography. Based on these findings, the patient was diagnosed with bilateral gastrocnemius muscle rupture, and surgery was performed to reconnect the head of the ruptured muscle. Because the rupture occurred perpendicular to the muscle direction, the locking loop technique, a method of suturing severed tendons, was used to reduce the tension. After surgery, the cast was used to prevent further injuries and promote voluntary rehabilitation. Follow-up was completed, with the calf showing normal posture and gait 112 days after surgery. This is the first case report in the Republic of Korea describing the successful diagnosis and treatment of bilateral gastrocnemius muscle rupture in a calf.

• 대한토목학회논문집
• /
• 제29권2C호
• /
• pp.41-49
• /
• 2009

구조물의 대형화와 재료비의 증가로 인해 다수의 기성말뚝을 대체할 수 있는 대형 현장타설말뚝의 사용이 증가하고 있다. 특히, 지하연속벽공법이 적용된 현장의 기초시공에 따른 시공성 및 경제성을 향상시키거나 토사층이 깊게 분포한 경우 공벽의 안정성을 확보하기 위한 기초형식으로 바렛말뚝의 사용이 증가하고 있는 실정이다. 본 논문에서는 국내 4개 현장을 대상으로 바렛말뚝을 시공하고 양방향 재하시험을 실시하여 말뚝의 지지력 및 침하특성을 고찰하였다. 또한 하중전이분석을 통하여 주면마찰력의 평가를 위한 ${\beta}$값을 분석하여 비교 평가하였고 3차원 유한요소해석을 통하여 양방향재하시험에 따른 경계면 효과와 하중-침하특성을 살펴보았다.

• Structural Engineering and Mechanics
• /
• 제84권3호
• /
• pp.311-321
• /
• 2022

In the buildings with long spans and high floors, such as logistics warehouses and semiconductor factories, it is difficult to install supporting posts under beams during construction. Therefore, the size of structural members becomes larger inevitably, resulting in a significant increase in construction costs. Accordingly, a prestressed hybrid wide flange (PHWF) beam with hollowed steel webs was developed, which can reduce construction costs by making multiple openings in the web of the steel member embedded in concrete. However, since multiple openings exist and prestress is introduced only into the bottom flange concrete, it is necessary to identify the shear resistance mechanism of the PHWF beam. This study presents experimental shear tests of PHWF beams with hollowed steel webs. Four PHWF beams with cast-in-place (CIP) concrete were fabricated, with key variables being the width and spacing of the steel webs embedded in the concrete and the presence of shear reinforcing bars, and web-shear tests were conducted. The shear behavior of the PHWF beam, including crack patterns, strain behavior of steel webs, and composite action between the prestressed bottom flange and CIP concrete, were measured and analyzed comprehensively. The test results showed that the steel web resists external shear forces through shear deformation when its width is sufficiently large, but as its width decreased, it exerted its shear contribution through normal deformation in a manner similar to that of shear reinforcing bars. In addition, it was found that stirrups placed on the cross section where the steel web does not exist contribute to improving the shear strength and deformation capacity of the member. Based on the shear behavior of the specimens, a straightforward calculation method was proposed to estimate the web-shear strength of PHWF beams with CIP concrete, and it provided a good estimation of the shear strength of PHWF beams, more accurate than the existing code equations.

• Steel and Composite Structures
• /
• 제50권3호
• /
• pp.319-336
• /
• 2024

Ultra-high-performance concrete (UHPC) has attracted increasing attention in prefabricated steel-concrete composite beams as achieving the onsite construction time savings and structural performance improvement. The inferior replacement and removal efficiency of conventional prefabricated steel-UHPC composite beams (PSUCBs) has thwarted its sustainable applications because of the widely used welded-connectors. Single embedded nut bolted shear connectors (SENBs) have recently introduced as an attempt to enhance demountability of PSUCBs. An in-depth exploration of the mechanical behavior of SENBs in UHPC is necessary to evidence feasibilities of corresponding PSUCBs. However, existing research has been limited to SENB arrangement impacts and lacked considerations on SENB geometric configuration counterparts. To this end, this paper performed twenty push-out tests and theoretical analyses on the shear performance and design recommendation of SENBs. Key test parameters comprised the diameter and grade of SENBs, degree and sequence of pretension, concrete casting method and connector type. Test results indicated that both diameters and grades of bolts exerted remarkable impacts on the SENB shear performance with respect to the shear and frictional responses. Also, there was limited influence of the bolt preload degrees on the shear capacity and ductility of SENBs, but non-negligible contributions to their corresponding frictional resistance and initial shear stiffness. Moreover, inverse pretension sequences or monolithic cast slabs presented slight improvements in the ultimate shear and slip capacity. Finally, design-oriented models with higher accuracy were introduced for predictions of the ultimate shear resistance and load-slip relationship of SENBs in PSUCBs.

• Advances in materials Research
• /
• 제13권3호
• /
• pp.243-251
• /
• 2024

The asymmetric polylactic acid (PLA) membrane was prepared via phase inversion method using non-solvent induced separation (NIPS) technique. This study aims to synthesized as well as to characterize the PLA membrane and evaluating the membrane performance on water flux and permeability. In addition, this research also studied the removal performance of methylene blue dye. The polymer solution has been prepared using 12 wt.% of PLA and dissolved in 88 wt.% of Dimethylacetamide (DMAc) as a solvent. Then, the cast film was immersed in different ratio of coagulant bath medium (distilled water: methanol: ethanol) ranging from 100:0:0, 75:25:0, 75:0:25 and 75:12.5:12.5, respectively). Several characterizations were performed which include, membrane contact angle and membrane porosity. Performance PLA membranes were determined in terms of water flux and permeability at 1 bar transmembrane pressure using dead-end permeation cell. Finally, methylene blue (MB) removal efficiency was tested at the same transmembrane pressure. The findings revealed that the increase of alcohol concentration in coagulant bath resulted in higher porosity and lower contact angle. In short, MB dye rejection efficiency is also closely related to the amount of alcohol ratio used in coagulant baths. Increases in concentration of methanol and ethanol in coagulant bath medium increases the membrane porosity thus increased in efficiency of methylene blue rejection.

• 한국구조물진단유지관리공학회 논문집
• /
• 제12권6호
• /
• pp.180-192
• /
• 2008

본 연구에서는 보다 자유로운 형상의 슬리브를 만들 수 있는 구상흑연 주철을 이용하여 보다 효과적으로 구조성능을 발휘하면서 SD500 고강도 철근에 적합하게 개발된 모르타르 충전식 슬리브 철근이음을 대상으로 실물크기의 19개 실험체를 제작하여 반복가력실험을 실시하였다. 그리고 강도, 강성, 슬립을 중심으로 한 구조성능에 대하여 본 실험의 주요한 변수에 따르는 영향을 분석하고, 국내기준을 비롯한 주요기준의 요구 성능과 비교하였다. 본 연구결과에서는 SD500 고강도 철근용으로 개발한 모르타르 충전식 슬리브 철근이음은 반복하중이 작용하는 경우에 대하여 국내기준을 비롯한 주요기준에서 요구하는 구조성능을 보유하고 있는 것이 확인되었고, SD500 고강도 철근용 모르타르 충전식 슬리브 철근이음에 대한 구조설계 기준 정립에 필요한 정량적인 기술 데이터를 제시하였다.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• 제21권3호
• /
• pp.257-265
• /
• 1999

골재생유도술에 의한 골재생과정의 생물학적 현상을 보다 구체적으로 이해하고자, 백서의 대퇴골에 인위적인 골결손부를 형성하고 비흡수성 차폐막을 설치한 다음 골재생유도 과정에서의 미세혈관의 구축 양상을 통상적인 광학 현미경적 소견 및 미세혈관주형 표본 관찰법을 중심으로 관찰한바 다음과 같은 결과를 얻었다. 광학 현미경적 소견의 초기 즉 술후 1주 및 2주 소견상 차폐막에 의해 피개된 실험부에서 보다 정연한 골성회복이 이루어졌으며, 이는 차폐막으로 인한 혈관망 형성의 양상에 의해 영향을 받는 것으로 나타났다. 즉, 차폐막에 의한 연조직 침입이 차단됨으로 인해 인접 골조직으로부터 수평적으로 들어온 혈관에 의해 규칙적인 혈관 분포를 나타내나, 대조군의 경우 연조직에서 유입된 혈관망에 의해 불규칙한 혈관망을 나타내었다. 시간이 경과되면서 재생된 결손부의 골은 재구성되면서 대조군과 실험군 사이에 골성회복의 양상은 유사하였으나, 인접 실험군의 골조직으로부터 유입된 혈관에 의해 형성된 규칙적인 혈관망이 연조직으로부터 침입한 혈관에 의해 그 규칙적인 배열이 흐트러진 대조군에 비하여 골성회복의 속도가 빨라진다는 사실을 확인하였다. 이상의 결과는 차폐막에 의한 골재생 유도과정에서 혈관의 유래와 혈관망의 정렬상태가 골성회복의 속도와 밀접한 관련이 있음을 보여주는 것이다.