• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.151-160
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• 1999

A series of laboratory tests for the marine clay sampled under the sea of Kwangyang bay have been conducted. The main types of tests are the general index property tests, the oedometer tests and the triaxial compression tests in both undrained(CIU) and drained(CID) conditions. The clayey samples, classified as CL, CH with natural water content of 38.3~84.6% and liquidity index of 0.71~0.98, are in the normally consolidated state with O.C.R. of 1.0l~l.60. The undrained stress path from CIU tests can be normalized with isotropic consolidation pressure$(p_0)$ and equal shear strain contour is linear passing through the origin in the (q, p) plot. The undrained shear strain is found to be the only function of the stress ratio($\eta$) and linear with intercept in the ($\varepsilon/\eta,\eta$) plot. The built-up pore pressure normalized with pc is also linear with respect to $\eta$. and its slope is defined by ´C´ as a pore pressure parameter. Equations to predict the undrained stress path and the shear strain are proposed. It is proved that the proposed equations give better agreements to the measured values than the Cam-clay theories. The failure points of the stress path are located on the same C.S.L. in (q, p) plot during both CIU and CID tests, which justifies the concept of critical state theory.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.303-311
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• 1998

Ten reinforced concrete rigid frames and infilled shear wall frames were tested under both vertical and cyclic loadings. Experiments were carried out to evaluate the structural performance of such test specimens, such as the hysteretic behavior, the maximum horizontal strength, crack propagation, and ductility etc. under load reversals. All the specimens were modeledin one-third scale size. Based on the test results reported in this study, the follwing conclusions can be made. For the rigid frame type and the fully rigid babel type shear wall specimens, the hysteresis diagrams indicate that the degradations of their strength were developed slowly beyond maximum carrying capacity. It was shown that when the hoop reinforcement ratio became higher, the energy dissipation capacity became larger and the failure mode became ductile. The specimens designed by the less hoop reinforcement for the fully rigid babel type shear wall, were mainly failed due to diagonal crack in comparison with the specimens designed by the larger hoop reinforcement ratio. Maximum horizontal resisting moment capacity of speciment designed by the fully rigid babel shear wall were increased by 5.47~7.95 times in comparison with the rigid frame type.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.41-47
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• 2010

The effect of PCB and BGA pad designs was investigated on the mechanical property of Pb-free solder joints. The mechanical property of solder joint was tested by three different test methods of drop impact tests, bending impact test, and high speed shear test. Two kinds of pad design such as NSMD (Non-Solder Mask Defined) and SMD (Solder Mask Defined) were applied with the OSP finished Pb-free solder (Sn-3.0Ag-0.5Cu, Sn-1.2Ag-0.5Cu). in the drop impact test and bending impact test, the characterized lifetime showed the same tendency, and SMD design showed better mechanical property of solder joint than NSMD regardless of test method, which was due to the different crack path. The fracture crack on SMD pad was propagated along the intermetallic compound (IMC) layer of solder joint, while the fracture crack on NSMD pad propagated through upper edge of land which shields pattern. In the high speed shear test, pad lift occurred on the solder joint of NSMD. SMD/SMD combination of pad design consequently illustrated the best mechanical property of BGA/PCB solder joint, followed by SMD/NSMD, NSMD/SMD, and NSMD/NSMD.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.207-218
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• 2013

One of the input parameters in the evaluation of seismic performance of rockfill dams is shear-wave velocity of rock debris and clay core. Reliable evaluation of shear-wave velocity by surface-wave methods requires overcoming the problems of rock-debris discontinuity, material inhomogeneity and sloping boundary. In this paper, for the shear-wave velocity investigation of rockfill dams, SBF (Short-Array Beamforming) technique was proposed using the principles of conventional beamforming technique and adopted to solve limitations of the conventional surface-wave techniques. SBF technique utilizes a 3- to 9-m long measurement array and a far-field source, which allowed the technique to eliminate problems of near-field effects and investigate local anomalies. This paper describes the procedure to investigate shear-wave velocity profile of rockfill dams by SBF technique and IRF (Impulse-response filtration) technique with accuracy and reliability. Validity of the proposed SBF technique was verified by comparisons with downhole tests and CapSASW (Common-Array-Profiling Spectral-Analysis-of-Surface-Waves) tests at a railroad embankment compacted with rock debris.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.17-25
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• 2004

The flat dilatometer test (DMT) is a geotechnical tool to estimate in-situ properties of various types of ground materials. The undrained shear strength is known to be the most reliable and useful parameter obtained by DMT. However, the existing relationships which were established for other local deposits depend on the regional geotechnical characteristics. In addition, the flat dilatometer test results have been interpreted using three intermediate indices - material index $(I_D)$, horizontal stress index $(K_D)$, and dilatometer modulus (E$_{D}$) and the undrained shear strength has been estimated merely using the horizontal stress index $(K_D)$. In this paper, the applicability of the flat dilatometer to Korean soft clay deposit has been investigated. Then an artificial neural network was developed to evaluate the undrained shear strength by DMT and the ANN, based on the $p_0, p_1, p_2, {\sigma '}_v$ and porewater pressure. The ANN which adopts the back-propagation algorithm was trained based on the DMT data obtained from Korean soft clay. To investigate the feasibility of ANN model, the prediction results obtained from data which were not used to train the ANN and those obtained from existing relationships were compared.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.457-463
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• 2016

The newly developed super ductile duplex stainless steel (SDSS) has good strength and ductility, and it can be used to reduce weight and improve the fabrication efficiency of a carbody of a rolling stock. In this study, spot weldability tests were conducted to take advantage of SDDSS in a carbody for an intermodal tram. Specimens of various thickness (0.4 to 5.0 mm) were prepared to find the proper welding conditions, and tensile load tests were conducted to evaluate the tensile-shear strength of spot welded joints. Then, nugget diameters were measured to verify the quality. The tensile-shear strength was found to be proportional to the heat parameter. It was verified that the tensile-shear strengths and nugget sizes of the joints satisfy the standard requirements. The overall weldability tests confirmed that SDDSS can be used effectively for the carbody of an intermodal tram.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.87-97
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• 2015

In this study, an experimental study was performed to evaluate the concrete breakout strength of cast-in-place(CIP) anchors in cracked concrete under static shear loading. The CIP anchors involved in this study were 30mm in diameter with an edge distance of 150mm and an embedment length of 240mm. The experiment was carried out for two specimens in uncracked concrete and three specimens in cracked concrete orthogonal and parallel to the direction of shear loading, respectively. Compared to the uncracked concrete specimen, cracked specimen orthogonal to the direction of shear loading showed no reduction in the concrete breakout strength and that parallel to the load direction about 91% strength which corresponds to 84% of uncracked concrete strength defined in ACI 318-11. Therefore, the experimental results showed smaller decrease in the shear resistance of CIP anchors in cracked concrete than that specified in ACI code which account for 71% strength of uncracked concrete in cracked concrete.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.77-77
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• 2009

ELV(; End of Life Vehicles)를 비롯한 최근 환경 동향은 자동차 전장 모듈에 대하여 다양한 무연 솔더 적용을 요구하고 있다. 특히 자동차 엔진룸과 트랜스미션은 가동 중 고온 및 진동의 지속적인 영향을 받기 때문에 이와 유사한 환경에서의 신뢰성 연구가 필요한 시점이다. 이에 본 연구에서는 Sn3.5Ag, Sn0.7Cu, Sn5.0Sb 솔더 조성에 대하여 복합환경 조건하에서 접합부 신뢰성을 평가하였다. 복합환경을 구현하기 위하여 $-40{\sim}150^{\circ}C$ 범위의 온도 사이클과 랜덤 진동을 동시에 인가하였으며, 진동 가속도 3G, 진동주파수는 10~1000Hz 로 설정하여 자동차 환경을 충족하였다. 복합시험의 1 cycle 은 20 시간이며, 총 120 시간의 시험 동안 진동의 영향 및 진동과 고온이 동시에 작용하였을 경우의 영향에 대해 비교하였다. 테스트 모듈 제작을 위해 450 um 의 솔더볼이 적용되었으며, 각 조성의 솔더볼을 이용하여 BGA test chip 제작하였고, 제작된 BGA test chip 은 다시 daisy chain PCB 위에 실장 및 리플로우 공정을 통해 접합되었다. 테스트 동안 In-situ 로 저항의 변화를 관찰하여 파단의 유무를 판단하였고 전자주사현미경을 통해 파괴 기전을 평가하였다. 복합시험 시간에 따른 전단강도를 측정하였으며, 각 조성에 대하여 상이한 전단강도 변화를 관찰하였다. 계면 IMC 형상은 전단강도 변화에 영향을 주었으며, 특히 높은 온도가 IMC 성장을 촉진시켜 전단강도 감소에 영향을 주었다. 본 복합환경 시험 조건에서는 Sn0.7Cu 가 가장 안정적이었으며, 파단면을 관찰한 결과 연성파괴 모드가 관찰되었다.

• Journal of the Korean GEO-environmental Society
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• v.14 no.1
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• pp.69-75
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• 2013

Suction stress is evaluated from soil water retention curves in order to deduce effective stress in unsaturated soils. $K_0$ consolidated triaxial tests were performed for silty sand to interpret effective stress in consolidation and shearing of unsaturated soils. Suction stresses from both consolidation stress and shear strength in triaxial tests were compared with those from soil water retention curves. The effective stresses on consolidation and shear strength are on each unique line, which are the same as that of the saturated case. It was found that the effective stress from soil water retention curves agrees with those from consolidation and shear strength in triaxial tests.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.503-510
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• 2009

Latex modified concrete (LMC) is a successful polymer-portland cement concretes, which have been developed and used for many years, in overlaying bridge decks and resurfacing industrial floors. The excellent bond strength to substrate, easy application and high resistance to impact, abrasion, wear, aggressive chemicals and freeze-thaw deterioration have made this material used widely. The objective of this study was to determine experimentally the load-deflection response and ultimate strength of reinforced RC beams. The cracking patterns and the mode of failure were observed. Because of excellent bond strength and repairing effects, the RC beams repaired by LMC at compression or tension zone showed over 100% recovery from damaged structures. The RC beams overlaid by LMC showed significant improvement at load carrying capacity as overlay thickness increases. However, the beams repaired of tension zone without shear stirrups almost showed no strengthen effect, and indicated an interfacial failures. The interfacial behavior was estimated by numerical method adopting the concept of shear flow.