• Journal of the Korean Wood Science and Technology
• /
• 제45권2호
• /
• pp.139-146
• /
• 2017

This study was conducted to develop a new drying technology in order to quickly and massively dry bamboo tubes without crack and check. The bamboo tubes with the diameter of 45 mm - 68 mm had been impregnated in the solution of PEG-1000, and then were dried under room temperature and high temperature, respectively. The cracks occurred on all control specimens while no cracks were found on PEG treated specimens during drying at room temperature due to effect of PEG restraining the circumferential shrinkage of bamboo tube. But the drying period of this method was too long (200 days) compared to 10 hours of kiln drying. During fast high temperature drying, cracks occurred on all control specimens, but no cracks were found on PEG treated specimens, which could be accounted for more solidified PEG due to higher drying temperature and faster drying rate, and the tension set formed on the surface of bamboo tube in the early stage of drying owning to high drying temperature and low relative humidity. Thus, it is advised that PEG treated bamboo tube should be fast dried at high temperature in order to not only prevent crack or check in short drying period but also increase the dimensional stability of the products made of bamboo tubes.

• Computers and Concrete
• /
• 제11권2호
• /
• pp.123-148
• /
• 2013

The nonlinear finite element method with eight noded isoparametric quadrilateral element for concrete and two noded element for reinforcement is used for the prediction of the behavior of reinforcement concrete structures. The disturbed state concept (DSC) including the hierarchical single surface (HISS) plasticity model with associated flow rule with modifications is used to characterize the constitutive behavior of concrete both in compression and in tension which is named DSC/HISS-CT. The HISS model is applied to shows the plastic behavior of concrete, and DSC for microcracking, fracture and softening simulations of concrete. It should be noted that the DSC expresses the behavior of a material element as a mixture of two interacting components and can include both softening and stiffening, while the classical damage approach assumes that cracks (damage) induced in a material treated acts as a void, with no strength. The DSC/HISS-CT is a unified model with different mechanism, which expresses the observed behavior in terms of interacting behavior of components; thus the mechanism in the DSC is much different than that of the damage model, which is based on physical cracks which has no strength and interaction with the undamaged part. This is the first time the DSC/HISS-CT model, with the capacity to account for both compression and tension yields, is applied for concrete materials. The DSC model allows also for the characterization of non-associative behavior through the use of disturbance. Elastic perfectly plastic behavior is assumed for modeling of steel reinforcement. The DSC model is validated at two levels: (1) specimen and (2) practical boundary value problem. For the specimen level, the predictions are obtained by the integration of the incremental constitutive relations. The FE procedure with DSC/HISS-CT model is used to obtain predictions for practical boundary value problems. Based on the comparisons between DSC/HISS-CT predictions, test data and ANSYS software predictions, it is found that the model provides highly satisfactory predictions. The model allows computation of microcracking during deformation leading to the fracture and failure; in the model, the critical disturbance, Dc, identifies fracture and failure.

• 대한금속재료학회지
• /
• 제47권12호
• /
• pp.811-818
• /
• 2009

In order to meet increasingly complex and rigorous technical specifications, extensive effort has been devoted to fabricate clad materials with multi-layered metal plates. In this study, novel stainless steel/aluminum/copper (STS/Al/Cu) three-ply clad materials were fabricated by a hot rolling process for cookware applications. The effect of the testing temperature on the mechanical properties of the clad materials and on each component metal was investigated during the tensile tests. The interface properties of the clad materials were also examined by optical microscopy (OM) and an electron probe micro-analyzer (EPMA). The best mechanical and interfacial properties for a warm working process were found in a sample annealed at a temperature of $300^{\circ}C$. For the sample annealed at $400^{\circ}C$, the results of the tensile test indicated that interface delamination occurred only in the region of the Al/Cu interfaces. This was due to the formation of the thick and brittle intermetallic compound of $Al_2Cu$ in the Al/Cu interface. In contrast, no interface delamination was observed in the STS/Al interface, most likely due to its strong bond strength.

• Composites Research
• /
• 제17권5호
• /
• pp.1-6
• /
• 2004

HDPE (high density polyethlyne) 라이너와 금속 boss를 가진 복합재료 압력용기가 필라멘트 와인딩 공정에 의해 개발되었다. 이 용기의 끝 부위는 dome-shape 부위 그리고 용기의 중앙부는 cylinder-shape로 형성되었다. 용기를 구성하는 재료인 HDPE, 수지 그리고 강화섬유와 같은 용기재료에 대해 환경실험이 1년 이상 실행되었다 Boss 설계는 FEM 해석으로 가스 누출을 최대한 방지해 주는 것으로 확인되었다. 실험적인 방법에 의해 가장 이상적인 fiber tension이 얻어졌고, image analyzer에 의해 측정된 섬유의 체적율, $\textrm{V}_{f}$,는 실린더에서 55.4 %, dome part에서 55.6 % 이었다. Winding pattern은 용기의 파괴가 실린더 부위에서 일어나도록 dome 부위의 복합재료 두께조절을 하도록 프로그램 되었다 경화 중 용기는 돌려졌었고 고정 내부압력 0.62 bar를 가함으로서 최종용기의 파괴압력이 28 % 향상되었다. Under-wound, fully wound된 용기의 파괴 및 피로시험결과를 충족하였다.

• Journal of Chest Surgery
• /
• 제42권2호
• /
• pp.165-174
• /
• 2009

배경: 심장 수술의 발전과 함께 자기 조직이 아닌 다른 인공 보철편의 필요가 늘어나 그에 따른 다양한 대체제가 연구 개발, 이용되고 있다. 본 연구는 더 나은 인공 조직보철편의 개발을 위해 이종이식 판막(돼지)과 심낭(돼지, 소)을 고정액에 따른 조직의 물리적 성질의 변화와 장력의 관계, 탄력도 변화, 열성 안정성을 알아보고자 하였다. 대상 및 방법: 이종이식 판막과 심낭을 처리하지 않은 그룹(fresh), glutaraldehyde (GA)로 고정한 그룹, glutaraldehyde (GA)에 ethanol 등과 같은 용매(solvent)를 첨가하여 고정한 그룹 세 그룹으로 나누어 검사하였다. 1) 각각의 군을 물리적 활성도 검사를 시행하였다. 2) 각 군별로 이종이식편의 일방향성 장력과 탄력도를 검사 비교하였다. 3) 소 심낭과 돼지 심낭을 각군 간에 열성 안정성 검사를 시행하였다. 결과: 1) 물리적 활성도 검사에서 촉진시 유의한 차이가 없었고, 봉합과, 신장도면에서 저농도 GA에 비해 GA+용매 처리군이 좀더 단단하게 느껴졌다. 2) 일반적으로 돼지의 대동맥, 폐동맥 판막의 원주방향 일방향성 장력과 탄력도는 아무것도 처리하지 않은 것보다 GA 혹은 GA+용매 처리 시 나아졌고, GA 혹은 GA+용매로 처리한 것 간에는 유의한 차이가 없었다(p>0.05). 소와 돼지의 심낭의 경우에도 GA 혹은 GA+용매로 처리한 것 간에는 유의한 차이가 없었다(p>0.05). 3) 각 실험과 군간에 GA 농도별로 비교 시 모든 군에서 그렇지는 않았지만, 고농도로 GA로 처리한 군(돼지의 폐동맥 판막, 돼지 심낭)에서 탄력도가 더 증가하는 경향이었다. 4) 소와 돼지 심낭 절편의 열 안정성 검사에서 GA 처리군과 GA+용매로 처리군간에 급격 수축 시점이 $80^{\circ}C$로 서로 차이가 없었다(소 심낭: p=0.057, 돼지 심낭: p=0.227). 결론: 이종 이식 보철편의 GA 고정 시 용매의 첨가는 압력-장력, 압력-탄력도, 열성 안정성 등 물리적 손실은 가져오지 않는 것으로 생각되며, 계속해서 더 나은 이식 보철 편 개발을 위한 여러 기능성 용매의 사용이나 세정 액의 연구개발이 필요하다.

• Clinics in Shoulder and Elbow
• /
• 제16권1호
• /
• pp.33-39
• /
• 2013

목적: 고령 환자의 상완골 원위부 골절에서 이중 강선 장력대 고정술을 이용한 수술의 임상적 결과를 분석하여 그 유용성을 알아보고자 한다. 대상 및 방법: 상완골 원위부 골절 환자 중 AO 분류상 C형 골절과 골다공증을 가진 65세 이상의 고령 환자에서 이중 강선 장력대 고정술을 이용해 관혈적 정복과 내고정을 시행 받은 10예를 대상으로 하였다. 남자가 1명, 여자가 9명이었으며 평균 연령은 74.6(66~84)세였다. 평균 추시 기간은 39.2(20~74)개월이었다. 골유합 유무, 시기와 주관절의 운동 범위를 측정하였고, Mayo 주관절 수행 점수, Jupiter 등에 의한 평가법을 이용하여 기능 상태를 평가하였다. 결과: 골유합은 10명에서 2차적인 전위 없이 이루어졌고, 평균 골유합 기간은 16.6(13~22)주였다. 최종 추시시 측정한 평균 주관절 운동범위는 굴곡 구축은 8.5 (0~15)도, 후속 굴곡 119(100~140)도, Mayo 주관절 수행 점수는 82(70~90)점으로 각각 우수 2예(20%), 양호 7예(70%), 보통 1예(10%)였다. Jupiter 등에 의한 평가법을 따르면 각각 우수 7예(70%), 양호 1예(10%), 보통 2예(20%)였다. 1예에서 이소성 골화가 있었으나 그에 따른 증상은 동반되지 않아 추시 관찰하기로 하였으며, 1예에서 강선에 대한 피부 자극 증상이 발생하여 장력대 강선 교체 수술을 시행하였다. 결론: 골다공증을 가진 고령 환자의 상완골 원위부 C형 골절의 수술적 치료에서 이중 강선 장력대 고정술은 견고한 고정과 동시에 조기 관절 운동을 가능하게 하여 효과적이며 우수한 치료법으로 사료된다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2000년도 추계학술대회 논문집
• /
• pp.823-826
• /
• 2000

Burr formed in drilling are classified into three types. no burr, burrs with cap, teared burr. To control burr size in drilling. the second type burrs with cap are to be formed because it is small and uniform. It is necessary to understand the mechanism of cap formation to derive the burr formation into second type burr with cap. In several materials, second type burrs are formed in drilling by changing cutting conditions. It is observed that cap is formed as a result of the plastic deformation along the outside of exit hole. According to the tension behavior of the material in concentrated region between hole and drill outside edge, the geometry of burr with cap is determined.

• 한국해양공학회지
• /
• 제11권4호
• /
• pp.40-48
• /
• 1997

There are many research results as individual uni-axial tension creep test of heat-resisting materials. However, there are very few about the study on the high temperature creep test for the Initial Strain Method, and especially any study on it about the friction welded joints of SUH3 to SUH35. One of the important concerns is a reliable method of evaluating static creep properties. No reliable method seems available at present to evaluate or predict static creep properties. So, the reliable method to evaluate and predict them by the ISM and AE techniques was made.

• 한국정밀공학회지
• /
• 제18권10호
• /
• pp.200-207
• /
• 2001

Burrs farmed in drilling are classified into three types, no burr, burrs with cap, teared burr. To control burr size in drilling, the second type burrs with cap are to be formed because it is small and uniform. It is necessary to understand the mechanism of cap formation to derive the burr formation into second type burr with cap. In several materials. second type burrs are formed in drilling by changing cutting conditions. It is observed that cap is formed as a result of the plastic deformation along the outside of exit hope. According to the tension behavior of the material in concentrated region between hole and drill outside edge, the geometry of burr with cap is determined. Simplified 2D FEM analysis shows good prediction for burr formation.

• 한국공간구조학회논문집
• /
• 제22권2호
• /
• pp.47-55
• /
• 2022

In this study, we focus on the feasibility of structural topology optimization for a steel-timber composite beam design of optimally allocating glue-laminated timbers into a web with openings under the condition of given steel flanges. The motivation of this study is to topologically take maximal stiffness harmonizing both tension and compression performance of the steel-timber composite beam and become the eco-frandly timber design for buidling members. As a result of this study, the key web-openings allocation becomes triangle spaces, i.e., empty or no materials, of optimal topologies of both a pure timber plate and a steel flange-web timber plate without web-openings. Several applicable examples verify the effectiveness of topology optimization for steel-timber beams with web-openings.