• 한국해양공학회지
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• 제15권2호
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• pp.94-98
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• 2001

fatigue life and nondestructive evaluation were examined experimentally using surface crack specimen and compact tension specimen of 5083 aluminium alloy. Acoustic emission signals emanated during failure of aluminum alloys has been the subject of numerous investigations. Possible sources of AE during deformation have been suggested as the dislocations, fracture of brittle particles and debonding of these particles from the alloy matrix. Fatigue life and penetration behavior of long surface crack can be evaluated quantitatively using K values proposed by authors. The influence of stress ratio on the frequency characteristics of AE signals were investigated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기물성,응용부문
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• pp.74-76
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• 2002

The suspension insulators are subjected to harsh environment in service for a long time. Long term reliability of the insulators is required for both mechanical and electrical performances. We studied an analysing method to find out a deformation of brittle porcelain with a thermal expansion of cement for suspension insulator. These simulation analysis and experimental results show that cement volume growths affect severely to be mechanical failure ageing.

• 한국전산구조공학회논문집
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• 제28권3호
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• pp.309-316
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• 2015

상태 기반 페리다이나믹 모델은 일반적인 재료 구성 모델을 구현할 수 있고 비국부 영역 내에서 연결된 모든 결합의 변형을 통해 각 절점의 재료 응답이 결정되기 때문에 체적 및 전단 변형을 모두 표현할 수 있다. 따라서 상태 기반 모델은 복잡한 동적 취성 파괴 현상(분기균열, 2차 균열, 계단균열, 균열 유착 등)을 해석하는데 유용하다. 본 논문에서는 평면응력 탄성체에 대해 2차원 상태 기반 페리다이나믹 모델을 적용하고 에너지해방율과 페리다이나믹 에너지 포텐셜로부터 손상 모델을 구성하였다. 페리다이나믹 파괴 해석 모델을 통해 취성 유리 재료에 대해 균열 면에 평행한 압축 응력파가 균열 분기 패턴에 미치는 영향에 대해 조사하였다. 실험을 통해 관찰된 동적 균열 진전 및 분기 패턴에 대한 주요 특성들이 페리다이나믹 해석을 통해 확인되었다. 또한 강한 인장 하중 하의 계단균열과 이차균열 등이 상태 기반 페리다이나믹 시뮬레이션을 통해 잘 모사가 되는 것을 확인할 수 있었다.

• Geomechanics and Engineering
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• 제16권2호
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• pp.195-204
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• 2018

Based on theories of rock mechanics, rock fragmentation, mechanics of elasto-plasticity, and energy dissipation etc., a method is presented for evaluating the rock fragmentation efficiency by using plastic energy dissipation ratio as an index. Using the presented method, the fragmentation efficiency of rocks with different strengths (corresponding to soft, intermediately hard and hard ones) under indentation is analyzed and compared. The theoretical and numerical simulation analyses are then combined with experimental results to systematically reveal the fragmentation mechanism of rocks under indentation of indenter. The results indicate that the fragmentation efficiency of rocks is higher when the plastic energy dissipation ratio is lower, and hence the drilling efficiency is higher. For the rocks with higher hardness and brittleness, the plastic energy dissipation ratio of the rocks at crush is lower. For rocks with lower hardness and brittleness (such as sandstone), most of the work done by the indenter to the rocks is transferred to the elastic and plastic energy of the rocks. However, most of such work is transferred to the elastic energy when the hardness and the brittleness of the rocks are higher. The plastic deformation is small and little energy is dissipated for brittle crush, and the elastic energy is mainly transferred to the kinetic energy of the rock fragment. The plastic energy ratio is proved to produce more accurate assessment on the fragmentation efficiency of rocks, and the presented method can provide a theoretical basis for the optimization of drill bit and selection of well drilling as well as for the selection of the rock fragmentation ways.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1329-1335
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• 2005

An aluminum or CFRP (Carbon Fiber ReinfDrced Plastics)is representative one of light-weight materials but its axial collapse mechanism is different from each other. The aluminum member absorbs energy by stable plastic deformation, while the CFRP member absorbs energy by unstable brittle failure with higher specific strength and stiffness than those in the aluminum member. In an attempt to achieve a synergy effect by combining the two members, aluminum CFRP compound square members were manufactured, which are composed of aluminum members wrapped with CFRP outside aluminum square members with different fiber orientation angle and thickness of CFRP, and axial collapse tests were performed fur the members. The axial collapse characteristics of the compound members were analyzed and compared with those of the respective aluminum members and CFRP members. Test results showed that the collapse of the aluminum CFRP compound member complemented unstable brittle failure of the CFRP member due to ductile characteristics of the inner aluminum member. The collapse modes were categorized into four modes under the iuluence of the fiber orientation angle and thickness of CFRP. The absorbed energy Per unit mass, which is in the light-weight aspect was higher in the aluminum CFRP compound member than that in the aluminum member and the CFRP member alone.

• 한국주조공학회지
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• 제34권5호
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• pp.170-178
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• 2014

Using the Gleeble test, the effects of [Mn/S] ratios and the presence of sulfides on the high-temperature fracture morphology of heavy-section steel castings were analysed via the observations of the microstructures. The specimens for which the [Mn/S] ratio was in the range of 60~80 showed a ductile fracture morphology with an area reduction of more than 60%, while some specimens with similar [Mn/S] ratios showed a brittle fracture morphology with an area reduction of 0.0% due to the liquidation of sulfides at the grain boundary. The fracture morphology was classified into three types in the Gleeble high-temperature tensile test specimens. The first type showed dimple formation at the grain boundary, the formation of globular MnS sulfides, and plastic deformation of sulfides at an elevated temperature, indicating a needle-point type of ductile fracture with area reductions of 96.0~97.8%. The second type was a knife-edge type brittle fracture with an area reduction of 0.0% due to the film-type liquidation of sulfides at the grain boundary, band-type liquidation, and the liquidation of a terraced nipple pattern. The third type was the typical ductile fracture with an area reduction of 31.3~81.0%, in accordance with the mixture of dimples with in the grains and terraced nipple pattern at the grain boundary.

• 대한금속재료학회지
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• 제50권12호
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• pp.939-948
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• 2012

A 3-ply clad metal consisting of aluminum and copper was fabricated by roll bonding process and the microstructures and mechanical properties of the roll-bonded and post-roll-bonding heat treated Cu/Al/Cu clad metal were investigated. A brittle interfacial reaction layer formed at the Cu/Al interfaces at and above $400^{\circ}C$. The thickness of the reaction layer increased from $12{\mu}m$ at $400^{\circ}C$ to $28{\mu}m$ at $500^{\circ}C$. The stress-strain curves demonstrated that the strength decreased and the ductility increased with heat treatment up to $400^{\circ}C$. The clad metal heat treated at $300^{\circ}C$ with no indication of a reaction layer exhibited an excellent combination of the strength and ductility and no delamination of layers up to final fracture in the tensile testing. Above $400^{\circ}C$, the ductility decreased rasxpidly with little change of strength, reflecting the brittle nature of the intermetallic interlayers. In Cu/Al/Cu clad heat treated above $400^{\circ}C$, periodic parallel cracks perpendicular to the stress axis were observed at the interfacial reaction layer. In-situ optical microscopic observation revealed that cracks were formed in the Cu layer due to the strain concentration in the vicinity of horizontal cracks in the intermetallic layer, promoting the premature fracture of Cu layer. Vertical cracks parallel to the stress axis were also formed at 15% strain at $500^{\circ}C$, leading to the delamination of the Cu and Al layers.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.1021-1038
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• 2016

Considerable part of reinforced concrete building has suffered from destructive earthquakes in Turkey. This situation makes necessary to determine nonlinear behavior and seismic performance of existing RC buildings. Inelastic response of buildings to static and dynamic actions should be determined by considering both flexural plastic hinges and brittle shear hinges. However, shear capacities of members are generally neglected due to time saving issues and convergence problems and only flexural response of buildings are considered in performance assessment studies. On the other hand, recent earthquakes showed that the performance of older buildings is mostly controlled by shear capacities of members rather than flexure. Demand estimation is as important as capacity estimation for the reliable performance prediction in existing RC buildings. Demand estimation methods based on strength reduction factor (R), ductility (${\mu}$), and period (T) parameters ($R-{\mu}-T$) and damping dependent demand formulations are widely discussed and studied by various researchers. Adopted form of $R-{\mu}-T$ based demand estimation method presented in Eurocode 8 and Turkish Earthquake Code-2007 and damping based Capacity Spectrum Method presented in ATC-40 document are the typical examples of these two different approaches. In this study, eight different existing RC buildings, constructed before and after Turkish Earthquake Code-1998, are selected. Capacity curves of selected buildings are obtained with and without considering the brittle shear capacities of members. Seismic drift demands occurred in buildings are determined by using both $R-{\mu}-T$ and damping based estimation methods. Results have shown that not only capacity estimation methods but also demand estimation approaches affect the performance of buildings notably. It is concluded that including or excluding the shear capacity of members in nonlinear modeling of existing buildings significantly affects the strength and deformation capacities and hence the performance of buildings.

• 한국지구과학회지
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• 제21권3호
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• pp.302-314
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• 2000

옥천대 내의 옥천누층군과 조선누층군의 경계지역인 제천시 남부의 금성지역 내에는 선캠브리아 기반암인 당두산변성암복합체와 조선누층군인 도리층, 그리고 이들을 관입한 쥬라기 제천화강암이 분포한다. 당두산변성암복합체는 석영편암, 운모편암, 규암 및 페그마타이트 등으로 구성되어 있으며, 도리층은 주로 엽리상 석회암으로 구성된다. 연구지역 내의 지층들에서는 고생대 이후에 최소한 세 번의 변형작용의 영향이 인지된다. 당두산변성암복합체는 연구지역 내에서 세 곳에 분포하는데, 두 곳은 단층과 관련되어 분포하고, 한 곳은 도리층 내에 내암군으로 분포하고 있다. 당두산변성암복합체의 상승과 관련하여 이 연구에서는 두 번째 변형작용의 산물인 월굴리 및 당두산드러스트와 세 번째 변형작용 이후의 정단층인 중보들, 고교, 중전리단층들에 의해 당두산변성암복합체가 상승하여 현재와 같은 분포 상태를 보이는 것으로 해석되었다. 연구지역 서쪽의 부산변성암복합체는 연성변형작용에 의해서 상승하여 옥천누층군 내에 노출된 것으로 보고되어 있으나, 당두산변성암복합체는 취성 내지 반취성 변형작용에 의해서 상승하였다. 기존에 보고된 옥천누층군과 조선누층군이 고생대 이후 받은 변형작용 순서에 의하면, 변형작용은 시간에 따라서 연성에서 취성으로 바뀐 것으로 보고되어 있다. 따라서 아직 그 지질시대는 규명되지 못 하였지만, 당두산변성암복합체의 상승은 부산변성암복합체의 상승보다 후에 일어난 것으로 생각된다.

• Design & Manufacturing
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• 제13권4호
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• pp.10-16
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• 2019

Semiconductor chip is bonded to the substrate by melting solder bumps. In general, the chip bonding is applied by a Reflow process or a Thermo-Compression(TC) bonding process. In this paper, we introduce a Laser Assisted Thermo-Compression bonding (LATCB) process to improve the anxiety of the existing process(Reflow, TC bonding). In the LATCB process, the chip is bonded to the substrate by irradiating a laser with a uniform energy density in the same area as the chip to melt only the solder bumps and press the chip with a Transparent Compression Module (TCM). The TCM consists of a fused silica header for penetrating the laser and pressurizing the chip, and a piezoelectric actuator (P.A.) coupled to both ends of the header for micro displacement control of the header. In addition, TCM is a structure that can pressurize the chip and deliver it to the chip and solder bumps without losing the energy of the laser. Fused silica, which is brittle, is vulnerable to deformation, so the header may be damaged when an external force is applied for pressurization or a displacement differenced is caused by piezoelectric actuators at both ends. On the other hand, in order to avoid interference between the header and the adjacent chip when pressing the chip using the TCM, the header has a notch at the bottom, and breakage due to stress concentration of the notch is expected. In this study, the thickness and notch length that the header does not break when the external force (500 N) is applied to both ends of the header are optimized using structural analysis and Coulomb-Mohr failure theory. In addition, the maximum displacement difference of the P.A.s at both ends where no break occurred in the header was derived. As a result, the thickness of the header is 11 mm, and the maximum displacement difference between both ends is 8 um.