• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1794-1804
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• 1993

The thermal stress intensity factors for interface cracks of Griffith and symmetric lip cusp types under vertical uniform heat flow in a finite body are calculated by boundary element method. The boundary conditions on the crack surfaces are insulated or fixed to constant temperature. The relationship between the stress intensity factors and the displacements on the nodal point of a crack tip element is derived. The numerical values of the thermal stress intensity factors for interface Griffith crack in an infinite body and for symmetric lip cusp crack in a finite and homogeneous body are compared with the previous solutions. The thermal stress intensity factors for symmetric lip cusp interface crack in a finite body are calculated with respect to various effective crack lengths, configuration parameters, material property ratios and the thermal boundary conditions on the crack surfaces. Under the same outer boundary conditions, there are no appreciable differences in the distribution of thermal stress intensity factors with respect to each material properties. But the effect of crack surface thermal boundary conditions on the thermal stress intensity factors is considerable.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1158-1168
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• 1994

For BEM analyses of the impact problems of dissimilar materials, the connected multi-region method using perfect bonded conditions on the interface boundaries was added to two-dimensional Laplace transformed-domain BEM program for a single region analysis. It was confirmed that the BEM results of impact problems of a single-region and multi-regions for a homogeneous isotropic material are agreed well. The two-dimensional Laplace transformed-domain BEM program combined with connected multi-region method was applied to analyse several impact problems of dissimilar materials. Also the feasibility of BEM impact analyses was investigated for dissimilar materials by the analysis of the BEM results for impact problems of dissimilar materials in terms of physical aspects. As for an application, the two-dimensional Laplace transformed BEM concerning impact problems of cracks at the interface of dissimilar materials and the determinating process of the dynamic stress intensity factors by extrapolation method are presented in this paper.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.315-321
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• 2010

Co-cured single lap joints under cyclic tensile loads fail initially at the tip of the interface corner between the two adherents. The failure mechanism is complex because it is related to corrosion fatigue. Corrosion behavior at the interface affects the failure of the joints because corrosion deteriorates fatigue resistance. In this study, we clarified the cause of interfacial corrosion in co-cured single lap joints under cyclic tensile loads. The failure mechanism was also analyzed by observing the failed surfaces of specimens and the stress distribution along the interface. The surface roughness at the interface and the stacking sequence of the composite adherent were examined to investigate their effects on failure of the joint.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.25-31
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• 1995

발전 Plant는 고온.고압하에서 장기간 사용되며 파손발생시는 대형 사고로 확대되므로 경년에 따 른 운용기술의 확보가 현안 과제이다. 즉, 현재의 설비를 그대로 사용할 것인가 \ulcorner 또는 교체하여 야 할 것인가\ulcorner 그대로 사용한다면 취약부위는 어디이며 언제 보수하여야 하는가 \ulcorner 또 교체한다 면 그 시기는 언제인가 \ulcorner 에 대한 기술적 예측이 필요하다 수명예측기술은 이러한 의문에 대한 해답을 주는 Plant 설비 운용기술중 가장 최신 기술분야의 하나이다. 본고에서는 보일러 부분중 가장 사용조건이 가혹하고 교체하는데 많은 비용과 시간이 소용되는 최종과열기를 대상으로 균열 전파에 의한 수명예측에 관하여 기술코자 한다.

• Journal of Welding and Joining
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• v.7 no.2
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• pp.1-11
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• 1989

주철은 구조물 및 공업재료로써 오랫동안 사용되어 왔으나 이들 용접은 항상 어렵고 특별한 지 식과 기술을 계속 요구하고 있다. 최근 가격면에서 유리한 주철을 주강 및 단조품과 대체하여 사용이 증가하는 추세이다. 이는 주조공정의 고유한 유연성과 함께 합금설계, 주조기술 및 열처 리 분야에서 개선이 이루어지면서 가능해졌다. 이런 개발과 병행하여 주철을 용접할 필요성이 증가되었다. 옛날에는 용접의 어려움 때문에 주철용접은 제조중 생긴 주물결함 보수나 사용도중 생긴 균열에 대한 보수용접으로 국한되었다. 그러나 수년동안의 용접기술 개발과 금속학적인 영향에 대한 지식이 증대됨에 따라 주철끼리 또는 강과의 접합까지 용접의 범위가 넓어졌다. 본고에서는 주철용접을 이해하는데 필수적인 금속학적인 영향들에 대해 주철 종류별로 설명하고 이들을 용접하는데 있어 성공과 실패에 대한 이유등을 실례를 들어 기술하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2398-2406
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• 1993

Abdi's numerical method(ref.13) for representing a stress singularity by shifting the mid-side nodes of isoparametric elements is reviewed. A simple technique to obtain the optimal position of the mid-side nodes in quadratic isoparametric finite element is presented. From this technique we can directly obtain the position of the side-nodes adjacent to the crack tip. It is also observed that the present technique provides good accuracy for the expression of the opening displacement and the determination of the mid-side nodes for more wide range of material properties than that obtained by Abdicant the finite element method is applied to determine stress intensity factors for pressurized crack perpendicular to and terminating at the interface of two bonded dissimilar materials. A proper definition for stress intensity factors of a crack perpendicular to bimaterial interface is provided. It is based upon a near-tip displacement solutions on the crack surface for interface crack between two dissimilar materials. Numerical testing is carried out with the eight-node and six-node elements. The results obtained are compared with the previous solutions.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.389-396
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• 2001

This paper presents an analytical prediction of the fatigue behavior of reinforced concrete bridge piers under earthquake. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. In boundary plane at which each member with different thickness is connected, local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. The proposed numerical method for fatigue behavior of reinforced concrete bridge piers under earthquake will be verified by comparison with reliable experimental results.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.541-549
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• 2015

This study was conducted to experimentally investigate the seismic retrofitting performance of non-ductile reinforced concrete (RC) frames by introducing engineered cementitious composite (ECC) wing panel elements. Non-ductile RC frame tested in this study were designed and detailed for gravity loads with insufficient or no consideration to lateral loads. Therefore, Non-ductile RC frame were not satisfied on present seismic code requirements. The precast ECC wing panels were used to improve the seismic structural performance of existing non-ductile RC frame. A series of experiments were carried out to evaluate the structural performance of ECC wing panel elements alone a non-ductile RC frame strengthened by adding ECC panel elements. Failure pattern, strength, stiffness and energy dissipation characteristics of specimens were evaluated based on the test results. The test results show that both lateral strength and stiffness were significantly improved in specimen strengthened than non-ductile RC frame. It is noted that ECC wing wall elements application on non-ductile RC frame can be effective alternative on seismic retrofit of non-ductile building.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.884-894
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• 1987

Stress intensity factors for the bimaterial interface cracks are determined by the boundary element method employing the multiregion technique along with the double-point concept. For this purpose, the formulas relating the stress intensity factors to the crack surface displacements, which are applicable to both the homogeneous and the bimaterial systems, are derived and the accuracy of the results is discussed using the preexisting analytic solutions. Besides, the stress intensity factors for the edge-cracked bimaterial plates are computed with various crack lengths and shear modulus ratios under the biaxial and the uniaxial loadings, respectively, to demonstrate the dependence of stress intensity factors on the loading conditions and the material properties.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1705-1712
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• 1994

Hilbert problems are derived to evaluate thermal stress intensity factors for a partially insulated crack subjected to vertically uniform heat flow in infinite bonded dissimilar materials. In case of fully insulated crack surface, the present solutions of thermal stress intensity factors are reduced into the same as the previous results. For the homogeneous material, mode II thermal stress intensity factor only exists. However, in the bonded dissimilar materials, both mode I and II thermal stress intensity factors are obtained. Specially, in this case, mode II thermal stress intensity factor is dominent. Also, thermal stress intensity factors are strongly influenced by the material properties. Thermal stress intensity factors decrease when the degree of insulation decreases.