• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.155-163
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• 2008

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally bonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips. Specimens consist of 9 small-scaled specimens with the different post-tensioning level as a main test parameter. A control specimen and specimens with simply bonded CFRP strips have been manufactured to compare the structural performances of prestressed system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned CFRP strips reached the rupture strength of the CFRP strip. The cracking and yielding loads were also increased proportionally to the post-tensioning level, but the ultimate loads were nearly equal regardless of the post-tensioning level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.147-154
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• 2008

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally unbonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips using embedded or stud-type plate anchorages. Total 10 small-scaled specimens were manufactured with the different post-tensioning level and types of mechanical anchorage as a main test parameter. A control specimen and specimens with simply bonded CFRP strips were included to compare the structural performances of each system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned unbonded CFRP strips reached the rupture strength of the CFRP strip. Also, it was observed that the specimens with stud-type anchorage have equivalent strengthening performance compared with embedded-type anchorage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.384-384
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• 2009

에폭시 수지에 유기화된 층상실리케이트 나노입자를 1wt% 충진한 경우 나노콤포지트와 마이크로 입자를 50wt% 충진한 경우 마이크로 콤포지트를 제조하였다. 초음파 분산법을 이용하여 나노 및 마이크로입자를 120분 동안 분산시킨 에폭시- 나노/마이크로 콤포지트이다. 나노콤포지트와 마이크로콤포지트의 단시간 교류절연파괴특성을 조사하기 위해 와이블 분포 plot을 통하여 나타내었다. 와이블 plot은 기울기로서 형상파라미터를 나타낸 경우로서 이는 파괴강도의 균질성을 의미하게 된다. 63.2% 누적분포함수를 나타낸 경우 척도파라미터로서 나타내어진다. 마이크로 콤포지트의 경우 형상파라미터가 2.99, 나노콤포지트는 8.96를 나타내었다. 또한 마이크로 콤포지트 및 나노콤포지트 스케일 파라미터는 164.25kV/mm, 245kV/mm를 얻었다. 또한 B10수명의 경우 마이크로콤포지트와 나노콤포지트의 경우 77.57kV/mm, 139.3 6kV/mm로서 나노콤포지트의 경우 완전하게 박리가 일어난 경우이다. 마이크로 입자를 분산시켜 입자간거리와 나노입자를 분산시켜 박리가 일어난 경우 입자간거리는 대단히 큰 차이를 나타내고 있다. 나노입자가 교번전계 하에서 주입된 전하 및 케리어 이동을 억제하는 경우로 이와같은 결과를 얻을 수 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2139-2157
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• 1994

In order to understand the delamination between leadframe and epoxy molding compound in an electronic packaging of surface mounting type, the stress intensity factor, T-stress and J-integral in fracture mechanics are obtained. The effects of geometry, material properties and molding process temperature on the delamination are investigated taking into account the temperature dependence of the material properties, which simulates as more realistic condition. As the crack length increases the J-integral increases, which suggest that the crack propagates if it starts growing from the small size. The effects of the material properties and molding process temperature on stress intensity factor, T-stress is and J-integral are less significant than the chip size for the practical cases considered here. The T-stress is negative in all eases, which is in agreement with observation that interfacial crack is not kinked until the crack approaches the edge of the leadframe.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.126-135
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• 2002

Plate bonding technique has been widely used in strengthening of existing concrete structures, although it has often a serious problem of premature falure such as interface separation and rip-off. However, this premature failure problem has not been well explored yet especially in view of local failure mechanism around the interface of plate ends. The purpose of the present study is, therefore, to identify the local failure of strengthened plates and to derive a separation criterion at the interface of plates. To this end, a comprehensive experimental program has been set up. The double lap pull-out tests considering pure shear force and half beam tests considering combined flexure-shear force were performed. The main experimental parameters include plate thickness, adhesive thickness, and plate end arrangement. The strains along the longitudinal direction of steel plates have been measured and the shear stress were calculated from those measures strains. The effects of plate thickness, bonded length, and plate end treatment have been also clarified from the present test results. Nonlinear finite element analysis has been performed and compared with test results. The Interface properties are also modeled to present the separation failure behavior of strengthened members. The cracking patterns as well as maximum failure loads agree well with test data. The relation between maximum shear and normal stresses at the interface has been derived to propose a separation failure criterion of strengthened members. The present study allows more realistic analysis and design of externally strengthened flexural member with steel plates.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.287-288
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• 2008

에폭시-층상실리케이트 나노콤포지트의 균질분산과 층상실리케이트내로 침투되는 박리정도를 향상시키기 위해 친환경적 분산기법인 물리적방법으로 Homogenizer와 Power Ultrasonic를 적용한 기법을 실시하였다. Homogenizer의 최적속도를 얻기 위해 분산시킨 나노콤포지트의 박리정도, 유리천이온도를 구할 수 있었고, Homogenizer와 Ultrasonic을 동시에 적용하여 최적시간을 구하기 위해 적용된 나노콤포지트를 절연파괴 강도의 Weibull Plots을 통하여 판단할 수 있는 좋은 결과를 얻을 수 있었다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.4
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• pp.401-409
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• 2009

This paper presents a method of calculating the stress intensity factor (K) and crack propagation direction (${\theta}_0$) at the crack-tip that is associated with delamination in the large scale integration(LSI) package. To establish a reasonable strength evaluation method and life prediction, it is necessary to assess fracture parameters under various fracture conditions. Therefore, we conducted quantitative stress singularity analysis considering thermal stress simulating the changes of crack length (a), (h) and (v) in delamination using the 2-dimensional elastic boundary element method (BEM), and from these results predicted crack propagation direction and path.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.98-105
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• 2016

In this study, projectiles with 2 kinds of nose shape: spherical and flat were impacted into normal concrete and fiber reinforced concrete panels. The fracture depth and form, crater diameter, tensile strain at rear face were evaluated. It was confirmed that smaller projectile nose areas resulted in deeper penetrations associated with concentrated impact forces and small front-face crater diameters in impact test. Conversely, larger projectile nose areas resulted in shallower penetrations and larger front-face fracture diameters. Similar front-face failure and strain distribution relationships based on the projectile nose shape were observed for normal and fiber-reinforced concrete although the rear-face tensile strain and scabbing were significantly reduced by the fiber reinforcement. In addition, a direct relationship was confirmed between the penetration depth based on the projectile nose shape and the tensile strain on the rear face. Thus the impact strain behavior is required to predict the scabbing behavior with penetration depth.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.283-292
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• 2005

This paper predicts premature failure load of reinforced concrete beams by epoxy-boned partially steel plates. A parametric study is conducted to estimate premature failure load of beams such as with or without stirrups, unplated length ratio, steel and reinforcement ratio, shear span to depth ratio of reinforcement beam. By results of finite element analysis, it turned out that the unplated length played a dominant role in partially plated beams but reinforcement ratio and shear span to depth ratio effected the premature failure load. The approximate expression with regard to combined design variables is compared with experimental results. It shows closely agreement.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.11-15
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• 2010

In this paper, we focused on the optimization of bonding conditions for the successful thermo-compression bonding of electrodes between the RPCB and FPCB with Sn-Pb solder. The peel strength was proportionally affected by the bonding conditions, such as pressure, temperature, and time. In order to figure out an optimized bonding condition, fracture energies were calculated through F-x (force-displacement) curves in the peel test. The optimum condition for the thermo-compression bonding of electrodes between the RPCB and FPCB was found to be temperature of $225^{\circ}C$ and time of 7 s, and its peel strength was 22 N/cm.