• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.2
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• pp.86-91
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• 2008

Ships operating in littoral sea are likely to be subjected to accidental load such as stranding. Once she has damage on the hull structure, her ultimate strength will be reduced. This paper is to investigate the effect of the stranding damage on ultimate strength of ship structure by using a series of collapse tests. For the experiment, 720 mm $\times$720 mm in section and 900mm in length of five box-girder models with stiffeners were pre- pared. Of the five, one has no damage and faur have an diamond shaped damage which represents the shape of rock section in seabed. The damage size is different between models. Among the damaged models, the damages of 3 of them were made by cutting the plate and one by pressing to represent stranding damage. Experiments were carried out under pure bending load and the applied load and displacements were recorded. The ultimate strength is reduced as the damage size increases, as expected. The largest damaged model has the damage size of 30% of breadth and its ultimate strength is reduced by 21% than that of no damaged one. The pressed one has lower ultimate strength than cut one. This might be due to the fact that the plate around the pressed damage area effect negatively on the ultimate strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1585-1593
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• 2015

3D-structured (embossed) aluminum sheets have been used in the heat insulation purpose for automative exhaust parts because of increasing their surface areas and stiffness reinforcement imposed in making the embossing pattern. However, there are many restrictions in press forming of the embossed sheet compared with the flat sheet (non-embossed one) because of its difference in the mechanical properties and the geometrical 3-dimensional shape. In this paper we investigated the deformation characteristic of embossed aluminum sheet in the incremental sheet forming process which has frequently used in the design verification and the trial manufacturing of sheet products. The single point incremental forming (SPIF) experiments for the rectangular cone forming using the CNC machine with a chemical wood-machined die and a circular tool shape showed that the formability of the embossed sheet are better than that of the flat sheet in view of the maximum angle of cone forming. This comes from the fact that the embossed sheet between the tool and the elastic die wall is plastically compressed and the flatted area contributes to increase the plastic deformation. Also the tool path along the outward movement from the center showed a better formability than that of the inward movement from the edge. However the surface quality for the tool path along the outward movement evaluated from the surface deflection is inferior than that of the tool path along the inward movement.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.867-873
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• 2003

$Si_{3}N_{4}$-BN based machinable ceramics were fabricated by hot-pressing at $1800^{\circ}C$ for 2 h under a pressure of 25 MPa. The microstructure, mechanical properties, and machinability were investigated. With increasing h-BN content from 5 vol% to 30 vol%, three point flexural strength decreased from 1000 MPa of monolithic S $i_3$ $N_4$ to 720～400 MPa. The fracture toughness, $K_{IC}$ , was decreased from 7.6 MPaㆍ$m^{1/2}$ of monolithic S $i_3$ $N_4$ to 6.5～4.1 MPaㆍ$m^{1/2}$. The grain size and aspect ratio of $\beta$-S $i_3$ $N_4$ slightly decreased with increasing h-BN content. S $i_3$ $N_4$ monolith could not be machined due to brittle fracture, but S $i_3$ $N_4$-BN based machinable ceramics could be machined without fracture, showing excellent machinability. With increasing h-BN content, the thurst force during cutting and micro-drilling process was decreased.

• Journal of the Korean Society of Clothing and Textiles
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• v.30 no.3 s.151
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• pp.386-395
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• 2006

Chitosan, a natural polymer has been used to nonwoven fabrics based polypropylene for sanitary top sheets. The changes in mechanical properties relating to the surface structure of functionally improved nonwoven fabrics were investigated with respect to the molecular weight and concentration of chitosan that was used. Low molecular weight(LMW) chitosan treated fabric was found to be evenly coated on the fabrics. It was shown that the bending and shearing characteristics of chitosan treated fabrics increased, which helped to make it stronger and harder, while shape stability improved following treatment using high molecular weight(HMW) chitosan. And the surface structure of treated fabrics was smooth and the sensitivity of its bulk improved somewhat. The treated fabrics were not overly stiff because the increase in Koshi value was not considerable compared to that of the bending characteristics. In the change of hand value relating to chitosan treated fabrics, THV generally improved. In the case of a 0.5$\%$ chitosan, HMW chitosan treated fabrics produced better THV than LMW chitosan treated fabrics. However, in the case of a 1.0$\%$ chitosan, THV of LMW chitosan treated fabrics produced outstanding results.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.4
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• pp.276-284
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• 2000

The acoustic emission (AE) behavior of reinforced concrete beams tested under flexural loading was investigated to characterize and identify the source of damage. This research was aimed at identifying the characteristic AE response associated with micro-crack development, localized crack propagation, corrosion, and debonding of the reinforcing steel. Concrete beams were prepared to isolate the damage mechanisms by using plain, notched-plain, reinforced, and corroded-reinforced specimens. The beams were tested using four-point cyclic step-loading. The AE response was analyzed to obtain key parameters such as the time history of AE events, the total number and rate of AE events, and the characteristic features of the waveform. Initial analysis of the AE signal has shown that a clear difference in the AE response is observed depending on the source of the damage. The Felicity ratio exhibited a correlation with the overall damage level, while the number of AE events during unloading can be an effective criterion to estimate the level of corrosion distress in reinforced concrete structures. Consequently, AE measurement characterization appears to provide a promising approach for estimating the level of deterioration in reinforced concrete structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.929-933
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• 2010

Four-point bending tests were performed to investigate the interfacial adhesion of Cu-Cu bonding fabricated by thermo-compression process for three dimensional packaging. A pair of Cu-coated Si wafers was bonded under a pressure of 15 kN at $350^{\circ}C$ for 1 h, followed by post annealing at $350^{\circ}C$ for 1 h. The bonded wafers were diced into $30\;mm\;{\times}\;3\;mm$ pieces for the test. Each specimen had a $400-{\mu}m$-deep notch along the center. An optical inspection module was installed in the testing apparatus to observe crack initiation at the notch and crack propagation over the weak interface. The tests were performed under a fixed loading speed, and the corresponding load was measured. The measured interfacial adhesion energy of the Cu-to-Cu bonding was $9.75\;J/m^2$, and the delaminated interfaces were analyzed after the test. The surface analysis shows that the delamination occurred in the interface between $SiO_2$ and Ti.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.635-643
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• 2017

The purpose of this study is to investigate the influence of the cold reduction rate and an ultrasonic fatigue test (UFT) on the fatigue behaviors of STS 304L. The tensile strength, yield strength, hardness value and fatigue limit in the UFT fatigue test linearly increased as thickness decreased from 1.5 mm to 1.1 mm, as the cold reduction rate of STS 304L increased. As a result of the UFT fatigue test (R = -1) of four specimens, the fatigue limit of the S-N curve formed a knee point in the region of $10^6$, and the 2nd fatigue limit caused by giga cycle fatigue did not appeared. In the case of t = 1.1 mm, the highest fatigue limit was 345 MPa, which was 64.3% higher than the original material (t = 1.5 mm). As a result of the UFT fatigue test of STS 304L, many small surface cracks occurred, grown, coalesced while tearing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4388-4397
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• 2015

The purpose of this study was to research the property change of acrylic resins depending on the induced-beam change and research the improved physical property of dry-heat and microwave-cured dental place acrylic resin in order to develop the acrylic resins with the optimum characteristic. As a result of observing flexural rigidity, hardness and color difference, the dry-heat-cured specimens of Vertex RS and Paladent 20 showed ideal property at 5, 15, and 25 kGy irradiation. The microwave-cured specimens of Vertex RS and Paladent 20 showed ideal property at 5 kGy irradiation. The correlation analysis showed a positive correlation among ARD, flexural rigidity (0 418), E coefficient (0.675) and Barcol hardness (0 588). The radiation cure technology is helpful for relieving the contamination caused by the manufacture of polymer composite. It can significantly contribute to the fusion of ultra violet cure technology and nano technology and the improvement of mechanical property without giving effect to the workability of polymer.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.222-222
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• 2003

나노크기 금속입자가 분산된 세라믹 나노복합재료는 향상된 기계적 특성과 함께 독특한 전기적, 자기적 특성을 보여주어 새로운 기능성 재료로의 응용가능성을 갖고 있다. 그러나 소결 중의 반응이나 입자성장 등으로 형성된 반응상 또는 조대한 입자상이 세라믹 기지의 입계 등에 존재한다면, 나노크기 금속상 분산에 의한 기계적 특성의 향상과 독특한 기능성 부여라는 장점들이 없어지게 된다. 따라서 요구되는 특성을 구현할 수 있는 금속분산 나노복합재료의 제조를 위해서는 미세조직 제어를 위한 최적의 제조공정 확립과 미세조직과 특성 등의 관계에 대한 연구가 요구된다. 본 연구에서는 기지상으로 A1$_2$O$_3$를, 분산상으로는 저융점 금속이며 일반적인 A1$_2$O$_3$의 가압소결시에 (약 140$0^{\circ}C$) 액상으로 존재하는 금속 Cu를 선택하여 조성이 5 vol% Cu가 되도록 복합재료를 제조하였다. $Al_2$O$_3$와 CuO 원료분말들은 습식 및 건식 볼 밀링을 통하여 균일한 분말혼합체로 제조되었다. 혼합분말은 열간가압소결기 내에 장입한 후 35$0^{\circ}C$에서 30분 동안 H$_2$가스를 흘려주며 CuO를 Cu로 환원 처리하였다. 계속해서 H$_2$분위기를 유지하며 승온한 후, 각각 1000-145$0^{\circ}C$에서 분위기를 Ar 으로 치환하였다. 소결은 145$0^{\circ}C$에서 30 ㎫의 압력으로 1시간동안 행하였다 소결한 시편들은 직사각형 형태로 가공하였으며 표면은 0.5$\mu\textrm{m}$의 다이아몬드 입자로 연마하였다. XRD, SEM 및 TEM을 이용하여 상분석 및 미세조직관찰을 행하였다. 파괴강도는 3중점 굽힘 법으로 (3-point bending test) 측정하였다. 이때 시편 하부의 지지 점간의 거리는 30mm, cross-head 속도는 0.5 mm/min으로 하였고 5개의 시편을 측정하여 평균값을 구하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.36-36
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• 1999

한국중공업(주)에서 수행한 KSTAR 진공용기 시작품 제작이 완성됨에 따라 제작과 관련된 종합기술을 분석하여 보았다. KSTAR 진공용기 시작품(그림1)은 전체의 1/4섹터인 90도 부분으로서 NBI(Neutral Beam Injection) 포트를 포함하는 45도 섹터와 축소포트(Reduced Port)를 포함하는 45도 섹터를 각각 먼저 제작한 후 두 부분을 용접하여 최종 시작품을 완성하였다. 용접은 SMAW법과 GTAW법 등 두가지 방법을 사용하였으며, 초기 용접시는 용접 면적이 작기 때문에 GTAW법을 이용하였고, 마무리 용접과 같이 용접 면적이 넓고 거친 부분에는 SMAW법을 이용하여 용접하였다. 모든 용접이 완전통과 용접이기 때문에 구조적 안전 면에서 좋으나, 진공측면에서는 다소 미흡한 점이 있다. 시작품은 상하 대칭구조로서 원통부분, 원형부분, 원추부분, 너클부분 (그림2) 등으로 나뉘어 지며 이중 원형품은 금형을 이용하여 성형하였고, 나머지 부분은 굽힘가공 후 절단적업을 하였다. 진공용기 조립은 안쪽과 바깥쪽 내벽부터 용접한 후 폴로이달 리브를 용접하고 외벽을 용접한다. 수평포트와 수직포트를 위해 스터브를 용접한 후 미리 용접해둔 NBI 포트 및 축소포트를 부착시켰다. 용접부위의 누설시험을 위한 방법으로, 용접주위 표면에서 개구하고 있는 홈에 적색 침투액을 침투시켜 침투 후 이 액을 홈의 개구로부터 빨아 내어 용접부위 표면상태에서 실제의 홈의 폭보다 확대한 홈의 지시모양으로 나타내게 하여 누설여부를 알기 쉽게 하는 액체 침투 탐상법을 적용하였다. 지시모양의 크기가 5mm 이상인 부분에 대해서는 재용접을 하였다. 누설 시험으로 초음파 탐상시험이 본제품 제작시 수행되어야 한다. 완성된 시작품에 대해 3군데의 위치에서 각각의 부분들이 용접되기 전과 후에 치수를 각각 측정하여 비교하였다. 또한 포트들에 대해서도 용접 전후 치수를 각각 측정하였다. 이러한 측정은 줄자를 사용하여 측정하였으므로 차 후 3차원 정밀 측정이 수반되어야 한다. 이상과 같이 시작품 제작을 통하여 문제점을 파악하고 개선책을 마련함으로서 향 후 KSTASR 진공용기 본 제품 제작할 때 반영코자 한다.