• Computers and Concrete
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• 제9권4호
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• pp.257-273
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• 2012

Based on the heterogeneous characterization of concrete at mesoscopic level, Realistic Failure Process Analysis ($RFPA^{3D}$) code is used to simulate the failure process of concrete-filled tubular (CFT) stub columns. The results obtained from the numerical simulations are firstly verified against the existing experimental results. An extensive parametric study is conducted to investigate the effects of different concrete strength on the behaviour and load-bearing capacity of the CFT stub columns. The strength of concrete considered in this study ranges from 30 to 110 MPa. Both the load-bearing capacity and load-displacement curves of CFT columns are evaluated. In particular, the crack propagation during the deformation and failure processes of the columns is predicted and the associated mechanisms related to the increased load-bearing capacity of the columns are clarified. The numerical results indicate that there are two mechanisms controlling the failure of the CFT columns. For the CFT columns with the lower concrete strength, they damage when the steel tube yields at first. By contrast, for the columns with high concrete strength it is the damage of concrete that controls the overall loading capacity of the CFT columns. The simulation results also demonstrate that $RFPA^{3D}$ is not only a useful and effective tool to simulate the concrete-filled steel tubular columns, but also a valuable reference for the practice of engineering design.

• 한국재료학회지
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• 제33권11호
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• pp.439-446
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• 2023

Changes in the microstructure and mechanical properties of as-roll-bonded AA6061/AA5052/AA1050 three-layered sheet with increasing annealing temperature were investigated in detail. The commercial AA6061, AA5052 and AA1050 sheets with 2 mm thickness were roll-bonded by multi-pass rolling at ambient temperature. The roll-bonded Al sheets were then annealed for 1 h at various temperatures from 200 to 400 ℃. The specimens annealed up to 250 ℃ showed a typical deformation structure where the grains are elongated in the rolling direction in all regions. However, after annealing at 300 ℃, while AA6061 and AA1050 regions still retained the deformation structure, but AA5052 region changed into complete recrystallization. For all the annealed materials, the fraction of high angle grain boundaries was lower than that of low angle grain boundaries. In addition, while the rolling texture of the {110}<112> and {123}<634> components strongly developed in the AA6061 and AA1050 regions, in the AA5052 region the recrystallization texture of the {100}<001> component developed. After annealing at 350 ℃ the recrystallization texture developed in all regions. The as-rolled material exhibited a relatively high tensile strength of 282 MPa and elongation of 18 %. However, the tensile strength decreased and the elongation increased gradually with the increase in annealing temperature. The changes in mechanical properties with increasing annealing temperature were compared with those of other three-layered Al sheets fabricated in previous studies.

• Geomechanics and Engineering
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• 제36권6호
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• pp.619-629
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• 2024

To improve the utilization rate of phosphate tailings (PTs) and widen the sources of subgrade filler, the PTs is employed to modify clay, forming a PTs modified clay, applied in the subgrade. Accordingly, the environmental friendliness of PTs was investigated. Subsequently, an optimal proportion was determined through compaction and California Bearing Ratio (CBR) experiments. Afterward, the stability of mixture with the optimal proportion was further evaluated through the water stability and dry-wet stability experiments. Finally, via the gradation and microstructure experiments, the strength mechanism of PTs modified clay was analyzed. The results show that the PTs were classified in the non-hazardous solid wastes, belonging to Class A building materials. With the increase of PTs content and the decrease of clay content, the optimum water content and the swelling degree gradually decrease, while the maximum dry density and CBR first increase and then decrease, reaching their peak value at 50% PTs content, which is the optimal proportion. The resilient modulus of PTs modified clay at the optimal proportion reaches 110.2 MPa. The water stability coefficient becomes stable after soaking for 4 days, while the dry-wet stability coefficient decreases with the increase of cycles and tends to be stable after 8 cycles. Under the long-term action, the dry-wet change has a greater adverse impact than continuous soaking. The analysis demonstrates that the better strength mainly comes from the skeleton role of PTs and the cementation of clay. The systematic laboratory test results and economic analysis collectively provide data evidence for the advantages of PTs modified clay as a subgrade filler.

• 한국식품과학회지
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• 제49권1호
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• pp.44-49
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• 2017

아임계수 추출 기술을 이용하여 참당귀로부터 데쿠신, 노다케닌을 추출하고 HPLC, HPLC-ESI/MS를 이용하여 추출조건에 따른 유효성분을 정성 및 정량적으로 비교 분석하였다. 추출결과, 데쿠신과 노다케닌의 추출함량은 아임계수 추출법과 비교하여 열수 추출 방법을 이용하는 것이 약간 많거나 유사하였지만, 추출 시간은 아임계수 추출법이 5-10분 이내로 매우 빠르게 추출할 수 있는 장점이 있다. 그리고 총 페놀함량, 총 플라보노이드 함량은 아임계수 추출법이 우수하게 많이 추출됨을 확인 할 수 있었고, DPPH, ABTS 라디칼 소거능을 이용한 산화방지 효과도 아임계수 추출법이 우수하였다. 특히, 아임계수 추출 조건인 추출 온도와 추출 시간이 증가할수록 총 페놀함량 및 총 플라보노이드 함량, 그리고 산화방지 효과 또한 점차적으로 증가하는 경향을 나타내었고 높은 상관관계를 보였다. 이는 오직 물만을 사용하여 유효성분을 추출하는 친환경적이며 안전하고 독성이 없는 아임계수 추출의 잠재성과 우수성을 확인한 결과이며, 다양한 한약재뿐만 아니라 다른 식품 추출 산업에 응용하여 사용될 수 있을 것이다.

• 대한치과보철학회지
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• 제43권4호
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• pp.426-437
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• 2005

Statement of problem : Although zirconium oxide ceramics are more and more commonly used in restorative dentistry, for many clinical applications only limited data can be found in the literature. However it is quite clear that hydrofluoric acid etching is impossible with zirconia ceramics. Therefore, other bonding techniques are required in order to lute these materials adhesively. Purpose : The purpose or this study was to evaluate the effects of surface treatments on shear bond strengths between two resin cements and a zirconia ceramic. Materials and methods : Experimental industrially manufactured yttrium-oxide-partially-stabilized zirconia ceramic discs (Adens, Korea) were used for this study. The ceramic specimens divided into five experimental groups and a control group (as received). Five surface treatments were studied 1) sandblasting with 110$\mu$m $Al_2O_3$ at 3 bars pressure 13 seconds at a distance of 10 mm, 2) flame-treated with the Silano-Pen for 5 $s/cm^3$, 3) grinding with a diamond bur. 4) sandblasting + Silano-Pen treatment, 5) diamond bur preparation + Silano-Pen treatment. Acrylic plastic tube (5 mm in height and 3 mm in diameter) were filled with composite to fabricate composite cylinders The composite cylinders were bonded to the ceramic specimens with either Superbond C&B or Panavia F resin luting agents. All cemented specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min; the maximum load at fracture was recorded. Sheat bond strength data were analyzed with oneway analysis of variance and Tukey HSD tests (P<.05). Treated ceramic surfaces and fracture surfaces after shear testing were examined morphologically using scanning electron microscope. Results: Ceramic surface treatment with Silano-Pen after sandblasting improved the bond strength of Superbond C&B resin cement. Supevbond C& B resin cement at Silano-Pen aiker sandblasting($27.4{\pm}3.8MPa$) showed statistically higher shear bond strength than the others. Conclusion: Within the limitation of this study, Superbond C& &B resin cement are suitable for cementation of zirconia ceramics and flame-treated with the Silano-Pen after sandblasting is required to enhance the bond strength.

• 한국의학물리학회지:의학물리
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• 제20권2호
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• pp.80-87
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• 2009

비혈관 스텐트(식도용, 담도용, 대장용, 십이지장용, 기관지용) 재질로 가장 널리 사용되고 있는 Nitinol wire 형상기억합금의 기계적 특성 향상을 위해 초음파 나노표면 개질(UNSM) 기술을 적용하여 Nitinol wire의 상변화와 초탄성 특성 및 표면 잔류응력 등의 변화를 연구하였으며, 탄력에너지와 부식내구성을 통한 스텐트의 수명 연장방법을 연구하고자 하였다. 본 연구에 사용된 Nitinol wire는 ${\phi}1.778$ mm로 UNSM 처리 전후의 표면거칠기 값은 Ra=0.092${\mu}m$와 Ra=0.093${\mu}m$로 비슷 하였지만, 초기시편에서는 미세결함과 인발가공 흔적이 확연히 관찰되었으나, UNSM 후에는 인발가공 흔적과 미세 표면 결함은 사라진 것이 발견되었다. 또한 잔류응력 측정 결과, 초기 시험편에는 +3.65 MPa였으나 UNSM 처리 후에는 -4.09 MPa로 확인되었으며, XRD를 통한 결정구조 분석 결과 $42.28^{\circ}$에서 초기보다 약한 (110) 오스테나이트 피크가 관찰되었으며, 대신 (020), ($1{\overline{1}}1$), 그리고 (021) 피크가 명확히 Martensite (B19' Monoclinic lattices) 구조로 확인되었고, (300)의 R상 (Rhombohedral lattices)에 대한 추가 피크가 미비하게 관찰되었다. 탄성변형에 따른 에너지 흡수력과 하중 제거에 따른 에너지의 회복력인 탄력계수(modulus of resilience) $U_r$은 단위체적당 변형률 에너지로 4.31 $MJ/m^3$에서 5.85 $MJ/m^3$로 증가하였다. 이와 같이 표면결함 제거와 인장응력을 압축응력으로 재편성하는 것만으로도 피로내구성을 크게 향상시킬 수 있다고 사료되며, 생체적합성과 더불어 내부식성, 내마모성 및 내구수명 향상을 실용화할 수 있는 표면개질 장치가 개발된다면, 현재 한국인 사망원인 1위인 순환계 질환(심근경색, 뇌졸중 등)에 사용되는 혈관계통의 스텐트 개발에도 응용개발연구가 가능할 것으로 예상된다.

• 구강회복응용과학지
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• 제23권3호
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• pp.249-257
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• 2007

State of problem : The use of zirconium oxide all-ceramic material provides several advantages, including a high flexural strength(>1000MPa) and desirable optical properties, such as shading adaptation to the basic shades and a reduction in the layer thickness. Along with the strength of the materials, the cementation technique is also important to the clinical success of a restoration. Nevertheless, little information is available on the effect of different surface treatments on the bonding of zirconium high-crystalline ceramics and resin luting agents. Purpose : The aim of this study was to test the effects of surface treatments of zirconium on shear bond strengths between bovine teeth and a zirconia ceramic and evaluate differences among cements Material and methods : 54 sound bovine teeth extracted within a 1 months, were used. They were frozen in distilled water. These were rinsed by tap water to confirm that no granulation tissues have left. These were kept refrigerated at $4^{\circ}C$ until tested. Each tooth was placed horizontally at a plastic cylinder (diameter 20mm), and embedded in epoxy resin. Teeth were sectioned with diamond burs to expose dentin and grinded with #600 silicon carbide paper. To make sure there was no enamel left, each was observed under an optical microscope. 54 prefabricated zirconium oxide ceramic copings(Lava, 3M ESPE, USA) were assigned into 3 groups ; control, airborne-abraded with $110{\mu}m$ $Al_2O_3$ and scratched with diamond burs at 4 directions. They were cemented with a seating force of 10 ㎏ per tooth, using resin luting cement(Panavia $F^{(R)}$), resin cement(Superbond $C&B^{(R)}$), and resin modified GI cement(Rely X $Luting^{(R)}$). Those were thermocycled at $5^{\circ}C$ and $55^{\circ}C$ for 5000 cycles with a 30 second dwell time, and then shear bond strength was determined in a universal test machine(Model 4200, Instron Co., Canton, USA). The crosshead speed was 1 mm/min. The result was analyzed with one-way analysis of variance(ANOVA) and the Tukey test at a significance level of P<0.05. Results : Superbond $C&B^{(R)}$ at scratching with diamond burs showed the highest shear bond strength than others (p<.05). For Panavia $F^{(R)}$, groups of scratching and sandblasting showed significantly higher shear bond strength than control group(p<.05). For Rely X $Luting^{(R)}$, only between scratching & control group, significantly different shear bond strength was observed(p<.05). Conclusion : Within the limitation of this study, Superbond $C&B^{(R)}$ showed clinically acceptable shear bond between bovine teeth & zirconia ceramics regardless of surface treatments. For the surface treatment, scratching increased shear bond strength. Increase of shear bond strength by sandblasting with $110{\mu}m$ $Al_2O_3$ was not statistically different.

• 한국포장학회지
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• 제5권1호
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• pp.47-55
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• 1999

탄수화물에서 유래되는 chitin은 cellulose와 유사한 $poly-{\beta}(1,4)-N-acetyl-D-glucosamine$의 섬유상의 중합체로서 물과 유기용매 녹지 않으나 acetyl amino group 을 탈아세틸화 시키면 키토 산으로 되어 묽은 산 용액에 용해되어 점성이 있는 용액이 되므로 화학, 의학 및 식품 산업분야 등에 다양한 용도로 이용되고 있다. 본 실험에서는 게 가공 폐기물로부터 부가가치가 높은 chitin 및 키토산 을 제조하였으며 침지조건을 달리하여 제조한 키토산의 특성을 조사하였다. 원료인 게껍질의 일반 성분은 수분 8.24%, 지방 3.65%, 단백질 28.73%, 회분 35.5%, chitin 23.55%로 나타났다. chitin의 제조는 5% HCl과 5% NaOH를 침지 온도와 시간을 달리하여 탈회분, 탈단백질하여 제조하였다. 탈회분은 온도에 따라 큰 변화는 없었으며, $30^{\circ}C$에서 30분 반응하였을 때 회분함량이 3.22%, 60분 후 1,07%로 감소했다. $50^{\circ}C$ 및 $70^{\circ}C$에서는 30분 처리하였을 때 1.46%, 1.19%를 나타낸 후 시간이 증가하여도 감소량이 뚜렸하지 않았다. 탈단백질은 위와 동일한 조건으로 침지하였으며 시간이 경과함에 따라 감소하였고 $70^{\circ}C$에서 90분 반응하였을 때 chitin의 질소 함량 6.92%에 근접하였다. 키토선 제조는 chitin을 50% Noah에 침지 시간을 달리하여 탈아세틸화하였다. 탈아세틸화도는 2시간 침지 후 82.84%를 나타내었으며 시간이 경과할수록 증가하였다. 한편 침지 후 여액의 NaOH를 다시 사용하였을 때 키토산의 점도 및 분자량은 시간의 경과에 따라 감소하였다. 즉 점도는 2시간 경과함에 따라 95 cps, 4시간 70 cps, 6시간 65cps, 8시간 60cps로 감소하였으며, 분자량은 110,286, 99,000, 96,666, 94,300으로 감소하였다. 횟수에 따른 점도 및 분자량은 시간의 경과에 따라 증가하였다. 반복 사용된 반응용액에서 제조된 키토산은 기계적인 물성변화는 거의 없었고, 각 solvent에서 반응시간 경과에 따라 약간 증가함이 있었고 acetic acid에 용해하여 제조한 chitosan film의 TS가 lactic acid chitosan film보다 우수함을 알 수 있었다. 수증기투과도의 경우 lactic acid에 용해하여 제조한 chitosan film이 acetic acid에 용해하여 제조한 chitosan film보다 큰 수증기 투과도를 보였다.