• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.113-116
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• 2003

The investigation of delamination growth behavior in hybrid composite material such as FRMLs should be considered delamination growth rate, dA_D/da$ using the delamination shape factor, $f_S$ instead of traditional fracture mechanics parameters. The main objective of this study is to evaluate the relationship between delamination element (i. e. delamination width, b, delamination contour, c, delamination shape factor, $f_S$ and delamination growth rate, dA_D/da$) and delamination growth in FRMLs under cyclic bending moment. The delamination shape formed along the fatigue crack between aluminum layer and glass fiber/epoxy layer are measured by scanning method. The details of study are as follow : ⅰ) Relationship between crack length, a and delamination width, b. ⅱ) Variation of delamination growth rate, dA_D/da$ was attendant on delamination shape factors, $f_{S1}$, $f_{S2}$, $f_{S3}$. The test result indicated the delamination growth behavior depends in delamination element such as delamination width, b, delamination shape factors, $f_{S1}$, $f_{S2}$, $f_{S3}$.

• Structural Engineering and Mechanics
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• 제34권6호
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• pp.685-702
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• 2010

In this paper, a nonlinear finite element procedure is presented for the dynamic analysis of reinforced concrete shell structures. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), was used. A 4-node flat shell element with drilling rotational stiffness was used for spatial discretization. The layered approach was used to discretize the behavior of concrete and reinforcement in the thickness direction. Material nonlinearity was taken into account by using tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach was incorporated. The low-cycle fatigue of both concrete and reinforcing bars was also considered to predict a reliable dynamic behavior. The solution to the dynamic response of reinforced concrete shell structures was obtained by numerical integration of the nonlinear equations of motion using Hilber-Hughes-Taylor (HHT) algorithm. The proposed numerical method for the nonlinear dynamic analysis of reinforced concrete shell structures was verified by comparison of its results with reliable experimental and analytical results.

• Journal of Welding and Joining
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• 제32권1호
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• pp.79-86
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• 2014

The purpose of this study is to determine the proper fillet weld size for the stiffeners on hull bottom plate of crude oil tanker. To achieve it, the effective notch stress and hot spot stress of the fillet weld with leg length specified in the rule were evaluated by using comprehensive FE analyses. Based on the results, the fatigue damages at each location of weld were calculated. Meanwhile the transitional behavior of initial welding distortion in the hull bottom plate under the design conditions was investigated by using a non-linear FEA. Welding distortion and residual stress introduced during fabrication process were considered as initial imperfections. According to FE analysis results, if the fillet leg length satisfies the design criteria of the classification society, the concern on the root failure at the fillet welds in the bottom hull plate during the design life can be negligible. In addition, considering the transitional behavior of the distortion during the service life, the fillet leg length should be minimized.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.127-132
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• 2002

Recent deepwater offshore structures in Gulf of Mexico utilize butt welded tubular joints. Application of welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical because the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimating the fatigue behavior of these tubular members in the design stage is generally conducted by using S-N curves specified in the codes and standards. Applying the stress concentration factor of the welded structure to S-N approach often results in very conservative assessment because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fracture mechanics and fitness for service (FFS) technology have been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves to be used and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. An attempt was made to develop set of S-N curves based on fracture mechanics approach by considering non-uniform stress distribution and a threshold stress intensity factor. Series of S-N curves generated from this approach were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02"). Similar comparison with API X′ was made for tubular joint.. These initial crack depths are larger than the limits of inspection by current Non-destructive examination (NDE) means, such as Automatic Ultrasonic Inspection (AUT). Thus a safe approach can be taken by specifying acceptance criteria that are close to limits of sizing capability of the selected NDE method. The comparison illustrates conservatism built into the S-N design curve.

• 한국전산구조공학회논문집
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• 제17권3호
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• pp.333-340
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• 2004

최근 장대화 되어가는 강교량의 건설 기술발전에 따라, 자중이 가벼운 강바닥판 형식의 교량 사용이 증가되고 있다. 그러나 강바닥판 교량은 피로에 매우 취약한 구조형식이며, 특히 종리브와 횡리브가 교차되는 상세부에서의 피로균열은 강바닥판 교량이 가지고 있는 가장 큰 문제점 중 하나이다. 이러한 피로균열의 발생원인은 횡리브의 면외거동에 의한 2차 응력으로부터 유발된다. 본 연구에서는 강바닥판 교량의 피로균열을 억제하고, 종리브-횡리브 교차연결부의 상세개선을 위해 3차원 실물모형체의 피로실험과 범용구조해석 프로그램인 LUSAS를 이용한 세부변수 해석을 병행하여 최적의 상세를 제시하기 위한 연구를 수행하였다. 연구 결과, 국내 표준단면 형상에 곡선형 벌크헤드 플레이트를 부착한 상세가 가장 유리한 것으로 나타났으며, 세부 변수해석에 의한 개선 단면 적용시 발생되는 응력값이 최대의 경우 약 50%이상까지 감소하는 것으로 나타났다. 응력의 감소와 함께 횡리브의 간격 증대(G=400)에 따른 4%의 강재량과 34%의 용접길이 감소로 제작원가 절감 및 피로에 유리한 강바닥판교의 제작이 가능하게 되었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부 C
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• pp.1010-1013
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• 1998

In micromechanical system (MEMS) such as microactuators. thin film has been widely used as structural material. MEMS materials have difference with bulk in terms of mechanical properties. So, we design the advanced test structure for micromechanical properties of MEMS. The designed structure includes the newly developed pre-crack and it is driven by electrostatic force. To measure the fracture toughness, the pre-crack formation in the test structure is developed with conventional etching process. The advanced test structure is fabricated by application of semiconductor technology. After this, we propose analytical methodology to evaluate the fracture toughness and fatigue properties through a prediction of crack behavior from the variations of stiffness and frequency. Additionally, life time of a mirror plane used in DVD(Digital Video Disk) is measured as a function of capacitance and applied voltage under the accelerated conditions. Ultimately, we propose the method to evaluate the micromechanical reliabilities of the MEMS materials using the advanced test structure.

• 대한기계학회논문집A
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• 제26권5호
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• pp.835-842
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• 2002

In this paper, static and fatigue bending strengths and failure mechanisms of CFRP (carbon fiber reinforced plastics) laminates having impact damages have been evaluated. Composite laminates used for this experiment are CF/EPOXY orthotropy laminated plates, which have two-interfaces $[0^0_ 4/90^0_4]_{ sym}$. A steel ball launched by the air gun collides against CFRP laminates to generate impact damages. The damage growth during bending fatigue test is observed by the scanning acoustic microscope (SAM) and also, the fracture surfaces were observed by using the SEM (scanning electron microscope). In the case of impacted-side compression, fracture is propagated from the transverse crack generated near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-B delamination in the case of impacted-side tension. Eventually, failure mechanisms have been confirmed based on the observed delamination areas and fracture surfaces.

• 콘크리트학회논문집
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• 제22권2호
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• pp.179-186
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• 2010

철근과 콘크리트의 부착은 콘크리트와 철근의 일체거동에 의한 안전성 확보를 위해서도 필요하지만, 적정수준의 연성을 확보하여, 부재의 거동을 조절하기 위해서도 필요하다. 현재까지 반복하중 하에서의 부착응력-슬립관계에 대한 연구는 진행되어 왔으나, 철근 부식이 이루어진 경우의 반복하중 하에서의 부착응력-슬립관계에 대한 연구는 거의 없는 실정이다. 따라서 이 연구에서는 부식된 철근의 부착 실험을 통하여 단조하중과 반복하중 하에서의 부식률에 따른 부착응력-슬립 관계를 살펴보았다. 실험결과로부터 철근 부식은 할열 균열이 발생하기 전까지는 단조하중에서의 부착강도를 증가시키는 것을 확인하였다. 그리고 반복하중 횟수와 반복하중 하에서의 슬립 및 잔류슬립을 이중로그스케일로 도시한 결과, 철근 부식이 있는 경우에도 철근 부식이 없는 경우와 마찬가지로 선형 관계임을 확인하였다. 그리고 부식에 의한 균열이 발생하지 않는 한, 철근 부식이 반복하중 재하 이후의 부착강도 및 부착강도에서의 슬립 등 부착 특성에 영향을 미치지 않는 것도 알 수 있었다. 마지막으로, 철근 부식으로 인한 균열이후에서의 응력수준에 따른 피로수명은 급격히 감소하는 것을 확인하였다. 이 연구에서 제시하는 철근 부식을 고려한 반복하중 하에서의 부착응력-슬립의 관계는 철근콘크리트 구조물의 내구수명 예측 시 유용하게 사용될 수 있을 것으로 사료된다.

• 한국자동차공학회논문집
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• 제20권5호
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• pp.53-64
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• 2012

Deep and narrow welds can be produced by laser welding at high welding speeds with a narrow heat-affected zone (HAZ) and little distortion of the workpiece. This study aims to evaluate the usefulness of laser welding at automobile component manufacture. Microstructure observation, hardness test, tensile test and fatigue life test are performed by using the fiber laser welded SPFC590 steel sheets which is used widely in the manufacture of automotive seat frame. Three kinds of specimens are only a SPFC590 steel plate, quasi-butt joint plate and lap joint plate by laser welding. The following results that will be helpful to understand the static strength, fatigue crack initiation and growth mechanism were obtained. (1) The tensile strength of quasi butt joint specimens nearly equal to base metal specimens, but lap joint specimens fractured in shear area of weld metal. (2) The fatigue strength of quasi-butt joint specimen was approximately 8 percent lower than that of the base metal specimens. Furthermore, the lap joint specimens were less than 86 percent of the base metal specimens. (3) The lap joint fatigue specimens fractured at shear area in high level stress amplitude, while fractured at normal area in low level stress amplitude. From these results, the applicability of the laser welding to the automobile component is discussed.

• 콘크리트학회논문집
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• 제15권2호
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• pp.163-172
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• 2003

최근 콘크리트 구조물이 점차 대형화, 고층화, 장대화 및 특수화 됨에 따라 강섬유 콘크리트의 적용이 요구되고 있다. 본 연구에서는 반복하중을 받는 강섬유를 혼입한 2경간 연속보에 대한 실험적 연구를 수행하여 피로하중에 의한 강섬유 혼입율(0%, 0.75%, 1.00%, 1.25%)에 따른 피로강도를 규명하고자 하였다. 정적실험을 통하여 극한하중, 초기 휨균열하중 등을 측정하였고 하중과 철근의 변형율 관계, 하중과 처짐 관계 그리고 하중증가에 따른 균열성장과 파괴양상 등을 관찰하였다. 피로실험을 통하여 반복횟수와 처짐 관계, 반복횟수와 변형율 관계 그리고 반복횟수에 따른 균열성장과 파괴양상을 관찰하였다. 피로실험 결과 강섬유를 혼입하지 않은 2경간 연속보는 정적극한강도의 60~70%에서 파괴되었고 S-N곡선으로부터 반복횟수 200만회에 대한 피로강도는 정적극한강도의 67.2% 전후임을 확인 할 수 있었다. 또한, 강섬유를 혼입한 2경간 연속보는 정적극한강도의 65∼85%에서 파괴되었고 S-N곡선으로부터 반복횟수 200만회에 대한 피로강도는 정적극한강도의 71.7%전후임을 확인할 수 있었다.