• 한국가스학회지
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• 제15권3호
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• pp.67-73
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• 2011

미래 수소경제시대에 가장 효과적이고 안전한 수소공급방안으로 배관이 적용될 것으로 예측되는데, 우선 첫 단계에서는 기존 가스배관의 수소공급배관 적용 가능성을 평가하는 것이 필요하다. 또한 국내 천연가스배관에 수소가 일부 포함된 대체천연가스가 주입되는 기존 가스배관의 건전성에 미치는 영향을 파악해야만 한다. 수소가 포함된 천연가스를 공급하는 배관에서는 수소취성, 피로파괴, 수소누설 등에 대한 검토가 이루어져야 한다. 본 논문에서는 고압천연가스배관 건전성에 미치는 수소의 영향 평가 작업의 하나로서. 배관재료의 기계적 특성 변화에 미치는 수소의 영향을 거시적으로 평가하기 위하여 인장시험을 수행하여. 수소 주입 전 후의 항복강도 및 인장강도의 변화를 측정하였고, 연성, 가공경화 지수, 항복비의 변화를 알아보았다.

• 한국세라믹학회지
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• 제56권2호
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• pp.205-210
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• 2019

Bioactive glass (BG) finds limited use as a bone replacement material owing to its low mechanical properties. In order to solve this problem, the micro-sized 13-93 BG was prepared as a fabric composite with SiC microfibers, and its mechanical properties and biocompatibility were investigated in this study. The tensile strengths of BG-SiC fiber-bundle composites increased in proportion to the number of SiC fibers. In particular, even when only one SiC fiber was substituted, the tensile strength increased by 81% to 1428 MPa. In the early stage of the in-vitro test, a silica-rich layer was formed on the surface of the 13-93 BG fibers. With time, calcium phosphate grew on the silica-rich layer and the BG fibers were delaminated. On the other hand, no products were observed on the SiC fibers for 7 days, therefore, SiC fibers are expected to maintain their strength even after transplantation in the body.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 춘계학술대회 논문집
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• pp.51-56
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• 2000

Demand for new nondestructive evaluations is growing to detect tensile crack growth behavior to predict long term performance of materials and structure in aggressive environments, especially when they are in non-visible area. Acoustic emission technique is well suited to these problems and has drawn a keen interests because of its dynamic detection ability, extreme sensitivity and location of growing defects. In this study, we analysed acoustic emission signals obtained in tensile test of high strength fire resistance steel for frame structure with time frequency analysis methods. The results obtained are summaries as follows ; In the T and TN specimen consisting of ferrite and pearlite grains, most of acoustic emission events were produced near yield point, mainly due to the dislocation activities during the deformation. However, B specimen under $600^{\circ}C$ - 10min had a two peak which was attribute to the presence of martensite phase. The first peak is before yield point the second is after yield point. The sources of second acoustic emission peak were the debonding of martensite-martensite interface and the micro-cracking of brittle martensite phase. In $600^{\circ}C$-30min to $700^{\circ}C$-60min specimens, many signals were observed from area before yield point and counts were decreased after yield point.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.141-144
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• 2005

Sensing and interfacial evaluation of Ni nanowire strands/polymer composites were investigated using Electro-micromechanical technique. Electro-micromechanical techniques can be used as sensing method for micro damage, loading, temperature of interfacial properties. Using Ni nanowire strands/silicone composites with different content, load sensing response of electrical contact resistivity was investigated under tensile and compression condition. The mechanical properties of Ni nanowire strands with different type/epoxy composites were measured using uniformed cyclic loading and tensile test. Ni nanowire strands/epoxy composites showed humidity and temperature sensing within limited ranges, 20 vol% reinforcement. Some new information on temperature and humidity sensing plus loading sensing of Ni nanowire strands/polymer composites could be obtained from the electrical resistance measurement as a new concept of the nondestructive interfacial evaluation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.35-39
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• 2008

In this study, electromechanical properties of carbon nanotube (CNT) thin film on flexible substrates were measured using a micro-tensile machine with functionality of simultaneous measurements of displacement, load and electrical resistance. The CNT thin film of about 100 nm thick was deposited on flexible substrates, polyethylene terephthalate (PET) using spraying and ink-jetting techniques. To investigate the effect of process condition on the electromechanical properties of CNT thin film, sets of CNT samples were fabricated under various heat treatments and microwave process. The microstructures of the CNT thin film before and after tensile test were investigated using Scanning Electron Microscope (SEM), and the failure modes of the CNT thin films were identified to understand their electromechanical behaviors and interaction with the flexible substrates. Based on the experimental results, the use of CNT thin film as flexible electrodes and strain gages is discussed.

• 한국주조공학회지
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• 제20권3호
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• pp.167-172
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• 2000

Squeeze casting was performed to fabricate the SiC whisker reinforced magnesium matrix composites, and the suitability of the squeeze casting for the production of the sound composites was determined by micro/macro-structures observations and tensile test. The two-directional infiltration of the melt and the removal of air during infiltration using the devised mold were necessary to produce the composites. The pressure of 100 MPa was effective for the production of composites with the SiC whisker volume fraction of 30%, but the pressure should be lower than 50 MPa in case of below 20% in the volume fraction. The SiC whiskers in the squeeze cast composites were randomly and densely aligned, and the SiC whiskers/magnesium interfaces were continuously well-bonded. The elastic modulus, 0.2% proof stress and tensile strength in the composite were about 2.5times, l0times and 4times as large as those of magnesium, respectively, indicating that the squeeze casting sufficiently provides the high strength magnesium composites reinforced with SiC whiskers.

• 한국주조공학회지
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• 제35권1호
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• pp.1-7
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• 2015

In this study, we investigated the effect of carbon on mechanical properties with different austempering conditions of high carbon(0.7~1.3wt.%C)-2.0wt.%Si steels. The specimens were austenitized at 850, 925 and $1020^{\circ}C$, and austempered at 260, 320 and $380^{\circ}C$ for the various period of time from 3 min to 300 min. After heat treatment, the evolution of stage I and stage II was identified with optical microscope, XRD and hardness test. When the austempering temperature was $260^{\circ}C$, the microstructure consisted of the lower ausferrite while the upper ausferrite micro-structure was formed at $380^{\circ}C$. As the austempering temperature increases from 260 to $380^{\circ}C$, the tensile strength decreases and elongation increases. In addition, when carbon content increases, tensile strength and elongation decrease.

• 한국구조물진단유지관리공학회 논문집
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• 제23권1호
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• pp.122-129
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• 2019

콘크리트에서 염소 이온과 같은 열화물질의 이동은 응력상태 및 재령의 증가에 기인한 공극구조에 따라 변화한다. 본 연구에서는 재령 28일, 91일, 그리고 365일 양생된 OPC 콘크리트의 압축 및 인장 하중조건을 고려하여 촉진탄산화 실험을 실시하였으며, 탄산화 거동을 평가하였다. KS F 2584에 의거하여 탄산화 속도계수를 도출하였는데, 하중을 고려하지 않을 경우 탄산화 속도계수는 재령 28일 대비 재령 91일은 50.0 % 수준으로, 재령 365일에서는 44.8 % 수준으로 감소하였다. 28일 재령 시, 하중의 영향으로 인해 인장재하영역에서는 103.9 ~ 108.8 % 수준으로 압축재하영역에서는 91.9 ~ 104.6 % 수준으로 변화하였다. 재령이 증가함에 따라 탄산화 속도는 크게 감소하였는데, 30 % 인장재하영역에서는 탄산화 속도계수가 1년 경과시 47.3 % 수준으로, 60 % 인장재하영역에서는 52.5 % 수준으로 감소하였으며 30 % 압축재하영역에서는 45.8 %로, 60 % 압축재하영역에서는 44.9 % 수준으로 감소하였다. 압축재하영역 30 %에서는 공극압밀로 인해 탄산화 속도계수가 감소하였으나 하중의 증가에 따라 압축재하영역 60 %에서는 미세균열의 영향으로 탄산화 속도계수가 증가하였다. 또한 인장재하영역은 압축부와는 다르게 탄산화 속도계수가 선형적으로 증가하는 경향을 나타내었다.

• 한국생산제조학회지
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• 제22권3호
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• pp.372-379
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• 2013

In this study, we investigated the traits of the clad metals used in hot-rolled clad steel plates. We examined the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516) under the specific circumstances of post heat treatment and whether a weld was multilayered and thick or repeated because of repairs. The test conditions were as follows. The clad steel plates were butt-welded using FCAW/SAW, and the heat treatment was conducted at $625^{\circ}C$, for 80, 160, 320, 640, or 1280 min. The change in the corrosion resistance was evaluated in these specimens. In the case of the carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro- hardness gradually increased and then decreased after 640 min. The elongation and contraction of the area increased gradually. An oxalic acid etch test and EPR test on STS316, a clad metal, showed a STEP structure and no sensitization. From the test results for the multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. In summary, the purpose of this study was to suggest some considerations when developing on-site techniques and evaluate the sensitization of stainless steels.

• Advances in Computational Design
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• 제7권2호
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• pp.129-137
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• 2022

Compo-casting method is one of the popular technique to produce metal based matrix composites. But, one of the main challenges in this process is un-uniform spreading of reinforced subdivisions (particles) inside the metallic matrix and the lack of desirable mechanical properties of the final produced composites due to the low bonding strength among the metal matrix and reinforcement particles. To remove these difficulties and to promote the mechanical properties of these kind of composites, the WARM ARB technique was utilized as supplementary technique to heighten the mechanical and microstructural evolution of the casted Al/Al₂O₃ composite strips. The microstructure evolution and mechanical properties of these composites have been considered versus different WARM ARB cycles by tensile test, average Vickers micro hardness test, wear test and scanning electron microscopy (SEM). The SEM results revealed that during the higher warm- ARB cycles, big alumina clusters are broken and make a uniform distribution of alumina particles. It was shown that cumulating the forming cycles improved the mechanical properties of composites. In general, combined compo-casting and ARB process would consent making Al/Al₂O₃ composites with high consistency, good microstructural and mechanical properties.