본 논문은 초탄성 형상기억합금의 복원성능에 의해 지속적으로 사용이 가능하고 마찰볼트 적용으로 에너지 소산 능력이 우수한 에너지 소산형 댐퍼를 제안하고 성능의 우수성을 입증하기 위해 구조용 탄소강이 적용된 댐퍼와 함께 해석을 통한 결과 비교 분석을 진행하였다. 해석결과에 대해 최대하중, 잔류변위, 에너지 소산등의 분석을 진행하여 초탄성 형상기억합금이 적용된 댐퍼의 우수성을 입증하였 으며, 해석 결과로 초탄성 형상기억합금이 적용됨에 따라 하중 성능과 잔류변위의 회복성능이 상당히 개선됨을 확인하였다. 최대하중의 경우 SSF댐퍼가 382.60kN으로 가장 우수하였으며 잔류변위의 경우 마찰볼트가 적용되지 않은 SS10, SS15가 0mm로 가장 우수한 회복거동을 보였다. 에너지소산의 경우 마찰볼트와 재료의 항복에 의한 연성효과가 우수한 CSF15가 가장 우수한 성능에 대한 거동 특성을 파악한다.

본 연구에서는 용접 여부에 따른 세 가지 유형의 철계-형상기억합금(Fe-Shape Memory Alloys, Fe-SMA)의 고주기 피로 거동에 대한 실험적 연구를 수행하였다. 본 연구를 위해 사용된 Fe-SMA은 스위스 EMPA에서 개발된 Fe-SMA으로, Fe-17Mn-5Si-10Cr-4Ni-1(V,C)의 화학적 조성을 가진다. 용접 여부 및 열처리 여부를 변수로 한 비용접, 용접, 열처리된 용접 시편이 ASTM E606/E606M 표 준에 따라 제작되었다. Fe-SMA의 재료적 특성을 평가하기 위해 직접 인장 실험 및 회복 실험이 수 행되었으며, 용접된 Fe-SMA의 피로 거동 평가를 위해 응력 진폭에 따른 피로 시험이 수행되었다. 피 로 시험은 최대 응력 수준을 Fe-SMA 극한 인장강도의 약 70%인 700MPa에서부터 100MPa씩 감소 시키며, 200MPa의 응력 범위까지 수행되었으며, 응력비(R)는 0으로 설정되었다. 피로 한계는 ASTM E1823-13에 따라 하중 반복 횟수 200만 회를 기준으로 하여 각 시편의 피로 한계를 확인하였다.

Steel plate shear walls (SPSWs) have been recognized as an effective seismic-force resisting systems due to their excellent strength and stiffness characteristics. The infill steel plate in a SPSW is constrained by a boundary frame consisting of vertical and horizontal structural members. The main purpose of this study was to investigate deformation modes and hysteretic characteristics of steel plate shear walls (SPSWs) to consider the effects of their aspect ratios and width-to-thicness ratios. The finite element model (FEM) was establish in order to simulate cyclic responses of SPSWs which have the two-side clamped boundary condition and made of conventional steel grade. The stress distribution obtained from the FEA results demonstrated that the principal stresses on steel plate with large thickness-to-width ratio were more uniformly distributed along its horizontal cross section due to the formation of multiple struts.

Recently, the demand for shape memory alloys in the biomedical industry is increasing. Nitinol alloy, which accounts for most of the shape memory alloy market, occupies most of the biomedical field. Nitinol for biomaterials requires a clean surface without sub-micron surface integrity and surface defects in order to be used more safely in a living body. Among them, new technologies such as polishing using MR fluid are being studied, but there is a disadvantage in that it takes a long time for processing due to a low material removal rate. In this study, material removal studies were conducted for effective polishing, and excellent polishing properties of MR fluid were confirmed.

Friction stir spot welding (FSSW) is a solid-state joining process and a rapidly growing dissimilar material welding technology for joining metallic alloys in the automotive industry. Welding tool shape and process conditions must be appropriately controlled to obtain high bonding characteristics. In this study, FSSW is performed on dissimilar materials AA5052-H32 aluminum alloy sheet and SPRC440 steel sheet, and the influence of the shape of joining tool and tool insertion depth during joining is investigated. A new intermetallic compound is produced at the aluminum and steel sheets joint. When the insertion depth of the tool is insufficient, the intermetallic compound between the two sheets did not form uniformly. As the insertion depth increased, the intermetallic compound layer become uniform and continuous. The joint specimen shows higher values of tensile shear load as the diameter and insertion depth of the tool increase. This shows that the uniform formation of the intermetallic compound strengthens the bonding force between the joining specimens and increases the tensile shear load.

Although the Ti–6Al–4V alloy has been used in the aircraft industry owing to its excellent mechanical properties and low density, the low formability of the alloy hinders broadening its applications. Recently, laser-powder bed fusion (L-PBF) has become a novel process for overcoming the limitations of the alloy (i.e., low formability), owing to the high degree of design freedom for the geometry of products having outstanding performance used in hightech applications. In this study, to investigate the effect of bulk shape on the microstructure and mechanical properties of L-PBFed Ti-6Al-4V alloys, two types of samples are fabricated using L-PBF: thick and thin samples. The thick sample exhibits lower strength and higher ductility than the thin sample owing to the larger grain size and lower residual dislocation density of the thick sample because of the heat input during the L-PBF process.

지진이란 지구 내부의 갑작스러운 에너지 방출로 땅이 흔들리는 자연재해의 일종으로 지표면에 살고 있는 사람들에 게 수많은 피해를 발생시킨다. 이에 따라 지진의 피해를 최소화하는 연구가 활발히 진행되고 있지만 지진 이후 발생한 구조물 의 잔류변형, 댐퍼와 구조물의 보수와 같은 문제는 피할 수 없다. 따라서 본 연구에서는 반영구적으로 사용이 가능한 초탄성 형 상기억합금을 댐퍼에 적용하고 제안한다. 본 연구의 에너지 소산형 댐퍼는 초탄성 형상기억합금과 더불어 마찰볼트가 추가됨으 로써 잔류변형은 적고 에너지 소산 및 하중 성능은 우수한 댐퍼이며 ABAQUS 프로그램을 활용한 유한요소해석을 진행하여 성 능을 입증한다. 재료의 차이, 마찰볼트의 유무, 핵심부재의 크기 차이를 설계 변수로 해석을 진행하여 도출된 힘-변위 거동응답 결과를 최대하중, 잔류변위, 에너지 소산 등의 성능에 대해 비교분석한다. 따라서, 연구 결과를 바탕으로 에너지소산형 댐퍼는 우수한 성능으로 안전한 사회기반을 조성하는 초석이 될 것으로 기대된다.

The electromembrane process, which has advantages such as scalability, sustainability, and eco-friendliness, is used in renewable energy fields such as fuel cells and reverse electrodialysis power generation. Most of the research to visualize the internal flow in the electromembrane process has mainly been conducted on heterogeneous ion exchange membranes, because of the non-uniform swelling characteristics of the homogeneous membrane. In this study, we successfully visualize the electroconvective vortices near the Nafion homogeneous membrane in PDMS-based microfluidic devices. To reinforce the mechanical rigidity and minimize the non-uniform swelling characteristics of the homogeneous membrane, a newly developed swelling supporter was additionally adapted to the Nafion membrane. Thus, a clear image of electroconvective vortices near the Nafion membrane could be obtained and visualized. As a result, we observed that the heterogeneous membrane has relatively stronger electroconvective vortices compared to the Nafion homogeneous membranes. Regarding electrical response, the Nafion membrane has a higher limiting current and less overlimiting current compared to the heterogeneous membrane. Based on our visualization, it is assumed that the heterogeneous membrane has more activated electroconvective vortices, which lower electrical resistance in the overlimiting current regime. We anticipate that this work can contribute to the fundamental understanding of the ion transport characteristics depending on the homogeneity of ion exchange membranes.

Recently, the medical industry’s use of biomaterial has taken an important place. A biomaterial is a semi-permanent material that can be used instead of a specific part of the body when there is a disability. Among them, Nitinol alloy has used in the human body, the material surface quality is very important, and research on processing methods is important to improve the surface quality. Therefore, in this study, a study was conducted to obtain high-quality surface quality using the MR polishing process. As a result, high-quality surface roughness was obtained at a wheel rotation speed of 400rpm(Ra=3.5nm).

High concentrations of fine particles are increasingly being detected due to inflows from abroad and local emission sources in Korea. As most people spend about 90% of their time indoors, the use of indoor air cleaners has grown significantly as they are now thought to be essential items. In this study, the noise, power consumption, and clean air delivery rate (CADR) of commercial air cleaners were analyzed according to the structural shape of the air cleaners. Analyses were performed based on the experimental results of 249 cases for air cleaners certified by Korea Air Cleaning Association. The air cleaners with front inlet and upper outlet air flow direction, which currently account for the highest market share, were found to have the highest noise per CADR (dB(A)/(m3/min)). On the other hand, the air cleaners with the inlet and outlet air flow in the same horizontal direction were found to have lowest noise per CADR than other structures.

최근 유기농산물에 대한 선호가 증가하고 있다. 유기농산물 생산에 있어 물리적 제초는 필수적이다. 하지만, 국내 밭 제초작업 기계화율은 60% 미만으로 낮으며, 농촌 인구의 고령화·여성화로 소형 제초기의 개발이 필요하다. 또한, 제초기의 경우 사용자가 반복적 진동에 노출되기 때문에 이를 절감할 수 있는 노력이 필요하나, 이에 대한 연구는 미흡한 실정이다. 따라서, 본 연구에서는 여성·고령 농업인도 사용하기 편리한 전동 배부식 중경제초기를 개발하는 데 있어 수평 회전식 원판에 부착된 제초날의 형상(원형, 삼각형, 일자형) 및 폭(15, 20, 25mm)에 따른 제초성능 및 ISO5349-1에 따라 손에 전달되는 진동을 분석하였다. 제초율은 원형 제초날에서 90.4~96.4%로 가장 높게 나타났으며, 진동 또한 원형 제초날을 사용하였을 때 사용자의 10%가 수지백증이 발병하는데 걸리는 시간이 20년 내외로 삼각형 및 일자형 제초날을 사용했을 때 보다 200% 가량 증가하는 것으로 나타났다. 따라서, 원형 제초날을 사용하였을 때 진동을 감소시킬 수 있으며, 불필요한 반력을 줄여 높은 제초효과를 볼 수 있을 것으로 판단된다.

This paper conducted a comparative analysis of the shear buckling characteristics of trapezoidal and sinusoidal corrugated steel plates considering of their initial imperfection. Initial imperfection refers to the state where the shape of the corrugated plate is initially not perfect. As such, an initially imperfect shape was assumed using the eigen buckling mode. To calculate the buckling stress of corrugated steel plates, the linear buckling analysis used a boundary condition which was applied to the plate buckling analysis. For the comparison of trapezoidal and sinusoidal corrugation, the shape parameters were assumed using the case where the length and slope of each corrugation were the same, and the initial imperfection was considered to be from 0.1% to 5% based on the length of the steel plate. Here, for the buckling analysis, ANSYS, a commercial FEA program, was used. From the results of buckling analysis, the effect of overall initial imperfection showed that the larger the initial imperfection, the lower the buckling stress. However, in the very thin model, interaction or local buckling was dominant in the perfect shape, and in this case, the buckling stress did not decrease. Besides, the sinusoidal model showed higher buckling stress than the trapezoidal one, and the two corrugation shapes decreased in a similar way.

Speaker is the converting device which change electric energy to sound energy, and we can easily see the speaker. They are widely used to home and car audio unit, home and industrial alarm device. Sometimes, the alarm sounds cause the environmental noise. Therefore it is important to design the appropriate speaker according to the installed device and position. In order to study the vibration and sound characteristics, the curvature of the cone paper is changed. Finite element method is used to compute the vibration characteristics and mode. Indoor and Vehicle teats are carried out to investigate the non-linear characteristics and the sound characteristics for some car speakers.

In this study, AlSi10Mg powders with average diameters of 44 μm are additively manufactured into bulk samples using a selective laser melting (SLM) process. Post-heat treatment to reduce residual stress in the as-synthesized sample is performed at different temperatures. From the results of a tensile test, as the heat-treatment temperature increases from 270 to 320oC, strength decreases while elongation significantly increases up to 13% at 320oC. The microstructures and tensile properties of the two heat-treated samples at 290 and 320oC, respectively, are characterized and compared to those of the as-synthesized samples. Interestingly, the Si-rich phases that network in the as-synthesized state are discontinuously separated, and the size of the particle-shaped Si phases becomes large and spherical as the heat-treatment temperature increases. Due to these morphological changes of Si-rich phases, the reduction in tensile strengths and increase in elongations, respectively, can be obtained by the post-heat treatment process. These results provide fundamental information for the practical applications of AlSi10Mg parts fabricated by SLM.

본 논문은 철계-형상기억합금(Fe-SMA)의 부식특성을 평가하기 위한 실험적 연구이다. 연구를 수행하기 위해 동전위 분극실험을 통해 Fe-SMA의 부식성능을 평가하였다. 시편을 3전극 플렛셀에 설치 후 전위차계를 이용하여 –200mV∼1000mV 구간의 전위를 2mV/s으 속도로 측정하였다. 기준전극 및 상대전극으로 각각 SCE 기준전극과 백금 와이어를 이용하였다. 동전위 분극곡선 및 타펠 피팅을 이용하여 부식전위 및 부식전류밀도를 측정하였다. Fe-SMA의 부식특성을 직관적으로 확인하기 위해 SD400 철근을 비교군으로 설정하였다. 염화물 환경에서 Fe-SMA의 부식성능을 확인하기 위해 3.5wt% 농도의 NaCl 용액에서 실험을 실시하였으며, 콘크리트 환경에서 Fe-SMA의 부식성능을 확인하기 위해 CaO를 이용하여 수용액의 pH를 13으로 조절하였다. 실험결과 Fe-SMA는 SD400 대비 모든 조건에서 우수한 내부식성이 나타났다. Fe-SMA의 콘크리트 환경에서 내부식성은 우수한 것으로 나타났다. 하지만 Fe-SMA가 염화물에 노출되면 부식저항이 급격히 감소되는 것으로 나타났다. 따라서 염화물에 직접적으로 노출되는 환경에서 Fe-SMA를 사용할 경우 부식을 방지하기 위한 적절한 조치가 필요할 것으로 사료된다.