• 열처리공학회지
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• 제17권6호
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• pp.327-335
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• 2004

Effect of spherodization of cementite on static and dynamic deformation behaviors of SCM415 steels was investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Three type of specimens were used with different spherodization degree of cementite. Dynamic test results were analyzed comparing with static tensile results and microstructural changes. The obtained results are as follows; 1) All the specimens of static and dynamic tests showed a ductile fracture mode of dimple. Specimens of the dynamic test showed adiabatic shear bands on the beneath of fracture surface. 2) In static tensile test, decreased tensile strength and increased uniform and non-uniform elongations appeared as spherodization degree of cementite increased. 3) In dynamic torsional test, decreased shear strength and increased uniform elongation appeared as spherodization degree of cementite increased. 4) Due to the largest uniform elongation, superior cold forgeability at high speed is expected on high spherodization degree of cementite.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.358-363
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• 2003

Spot welded structure is operated in diverse situation because of temperature, humidity and precipitation. In addition factors of environmental pollution such as acid rain, that courses corrosion, have the tendency to increase, But spot welded structure strength is affected by dampness and environment temperatures. Therefore, it is important to evaluate effect of temperature of spot welded part, In this study, the strength distribution of spot welded plates is evaluated about the environmental temperature of zine coated steel plates and test is conducted with welded part immersed in distilled and synthetic sea water. Specimens are immersed into water for 10, 100, 500 and 1000hours to evaluate the effects of water immersion time on tensile-shear strength under the conditions of -40, 0, 20 and $50^{\circ}C$. Strength is evaluated by tensile-shear test. The conditions of spot welding are 240kgf electrode force, 10KA welding current with 0 and 5mm clearance. From this study, spot welded specimens with clearance have lower tensile-shear strength in the distilled water or synthetic sea water comparing with spot welded specimens without clearance. And they have lower tensile-shear strength under $-40^{\circ}C$ and over $50^{\circ}C$.

• 대한조선학회논문집
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• 제55권3호
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• pp.205-214
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• 2018

This paper deals with the experimental study on the hygrothermal ageing effect to the strength of Carbon Fiber Reinforced Plastics (CFRP) materials for marine leisure boat manufactured by vacuum assisted resin infusion method. The experiments performed consist of tensile, flexural and shear tests according to American Society for Testing and Materials (ASTM) and Korean Industrial Standards (KS) test methods. Test coupons are varied from uni-directional(UD, $0^{\circ}$, $90^{\circ}$), Bi-Directional (BD), and Double-Bias (DB) carbon fiber fabrics in conjunction with epoxy resin. The results of tensile test show that tensile strength reduces significantly while not the same degree of reduction is observed for elasticity modulus with respect to the existence of hygrothermal ageing effect. This implies that the tensile strain induced from external load holds steady values but ultimate strength values change widely under hygrothermal ageing effect. In case of the flexural test, $0^{\circ}$ UD shows more strength reduction than $90^{\circ}$ UD while BD has reduced values in both flexural strength and elasticity modulus under hygrothermal ageing effect. It is learned that the bending strain induced from external load and ultimate strength values are reduced with respect to hygrothermal ageing effect. Shear test performed only on DB materials, and the results show marginal reduction in ultimate strength and moderate reduction in elasticity modulus. This means that the shear strain varies more than ultimate shear strength with respect to hygrothermal ageing effect. The experiment conducted in this paper clearly demonstrates the differences in material properties of the CFRP for the consideration of hygrothermal ageing effect. Findings obtained from this experimental study can serve as a fundamental input data for the realistic structural responses of marine leisure boat built in CFRP materials.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.493-502
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• 2022

Shear lag phenomenon has long been considered in numerous structural codes; however, the AISC provisions have now no longer proposed any unique equation to calculate the shear lag ratio in bolted connections for angles in general. It is noticeable that, however, codes used in this case are largely conservative and need to be amended. A parametric study consisting of 27 angle sections with equal legs and different with bolted connections was performed to investigate the effects of shear lag on the ultimate tensile capacity of angle members. The main parameters were: steel grade, connection length and eccentricity from the center of the plate, as well as the number of rows of bolts parallel to the applied force. The test results were compared with the predictions of the classical 1-x/l law proposed by Mons and Chesen to investigate its application to quantify the effect of shear lag. A parametric study was performed using valid FE models that cover a wide range of parameters. Finally, based on the numerical results, design considerations were proposed to quantify the effect of shear lag on the ultimate tensile capacity of the tensile members.

• 한국철도학회논문집
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• 제11권3호
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• pp.280-285
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• 2008

Gurson model과 shear failure model 두 가지 파괴모델을 이용하여 노치인장시험과 초기 균열을 가지는 파쇄튜브의 압축거동을 유한요소법으로 해석하였다. Shear failure model의 파라미터 값은 노치인장시편의 시험 및 해석을 통하여 결정하였다. 항복강도와 파괴전단변형률 등의 파라미터 값을 정한 후, Gurson model과 shear failure model을 파쇄튜브의 해석에 적용하였다. Gurson model과 shear failure model이 인장시편에 대하여는 비슷한 파괴 거동을 보여주지만 파쇄튜브의 압축력과 균열 성장 속도에서는 다른 결과를 보임을 확인하였다. 즉, shear failure model에서는 Gurson model에 비하여 균열이 전파되기 위해 더 큰 압축력이 요구되었다. 이러한 현상은 shear failure model 이 재질의 손상 과정에 대한 고려를 포함하고 있지 않기 때문인 것으로 생각된다. 어느 모델이 튜브의 해석에 적당한 지를 실험을 통하여 검증할 필요가 있다.

• 대한토목학회논문집
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• 제31권4A호
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• pp.303-309
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• 2011

적층고무받침은 지진격리 교량에서 면진장치로 주로 사용되고 있으며, 지진격리 설계시 적층고무받침의 성능 및 거동특성을 파악하는 것은 매우 중요하다. 적층고무받침의 주요 평가요소로는 압축 및 전단특성 그리고 인장특성으로 구분된다. 이 요소 중 압축특성 및 전단특성에 대한 특성실험 결과는 많으나, 인장특성에 대한 자료는 충분하지 않다. 이에 따라 본 연구에서는 인장하중을 받는 적층형 고무받침의 특성에 대해 연구를 수행하였다. 적층고무받침의 인장시험은 형상계수 및 전단변형 변화에 따른 기계적 특성에 대하여 검토하였다. 실험결과 인장변형이 증가 할수록 인장이력곡선은 비선형 특성을 보이며, 단순인장시험결과 300%이상 인장변형 후 파괴되었다. 반면에 전단변형된 상태에서 인장파괴는 약 40%이상의 인장변형 후 파괴되었다. 또한 형상계수가 낮을수록 극한인장 파괴성능이 저하되었다. 이와 같은 결과는 명확하지는 않지만 고무 층이 3축 인장 받을 경우 내부공극에 의해 균열이 확장되어 파괴가 발생하는 것으로 추측된다. 본 연구결과는 지진격리 구조물 설계시 인장하중에 대한 기초자료로 충분히 활용 가능할 것으로 판단된다.

• 한국산학기술학회논문지
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• 제12권6호
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• pp.2866-2871
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• 2011

본 연구에서는 생태축조블록을 적용한 보강토 옹벽의 국부적 안정성 검토에 필요한 보강재 인장력 계산법을 정립하고 국부적 안정성 검토와 관련한 주요 설계인자인 보강재와 블록 사이의 연결강도와 블록 접촉면 사이의 전단강도를 시험을 통해 규명하였다. 연결강도 시험결과에 따르면 생태축조블록의 내부를 흙으로 속채움하고 D13 이형철근을 사용할 경우 첨두 하중값은 이형철근의 허용인장력 정도임을 알 수 있었으며 D16 이형철근을 사용할 경우 첨두하중값은 허용인장력의 76% 정도였다. 생태축조블록의 내부를 콘크리트로 속채움하는 경우에 있어서 D10, D13 이형철근을 사용하였을 때의 연결강도는 각각의 이형철근의 허용인장력보다 크게 나타났다. 생태축조블록의 접촉면 전단시험결과를 통해 구한 전단저항 매개변수인 ${\alpha}_u$는 1.7kN/m 이었고 ${\lambda}_u$는 $27.6^{\circ}$ 이었다.

• Journal of Welding and Joining
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• 제18권1호
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• pp.52-58
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• 2000

Spot welding, namely a kind of electric resisting welding has been used widely in field of automobile and aircraft industries because of easiness to apply. Specimens used in this study was a mild steel of 1.2mm thickness and the electrode was a Cu-Cr alloy of 6mm diameter. The surface sheared of specimens after testing of tensile shear was observed by SEM(scanning electron microscope) after ultrasonic cleaning for 10min., and microstructures and grain size of all specimens were measured with using of O.M.(Optical microscope). By the means of measurement and observations of tensile shear load, fatigue strength and share surface, the weldability of spot welding was evaluated. When tensile shearing testing, fracture starting point in all specimens was took place at the bond between HAZ(Heat affected zone) and nugget. With increasing in number of layers, fatigue strength was decreased. With increasing in electric current, grain size in the HAZ became more fine.

• 한국레이저가공학회지
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• 제3권3호
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• pp.31-37
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• 2000

In this paper, the possibilities of the laser overlap spot welding were studied to utilize the advantageous properties of amorphous metal foils. In order to estimate the usage of amorphous metals foils as structural members, the tensile shear strength and the fracture features were investigated. Although the crystalline zone on the surface was formed, it was not the direct cause of the fracture of the weld. The fracture of the weld resulted from the geometry discontinuity between the workpiece and the protrusion zone, which was formed during the weld process. The vein pattern - the typical feature of the fracture of the amorphous metal - was formed on the fracture surface. The tensile shear stress was reached to 1200 N/㎟ (2-foils overlap welding) and 900 N/㎟ (10-foils overlap welding), whereas the tensile strength of the workpiece was 1500-2000 N/㎟.

• 한국공작기계학회논문집
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• 제12권1호
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• pp.32-37
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• 2003

Evaluation of fatigue strength on the spot welded part is very important for strength design of spot welded steel structures. In this paper, we could get the life cycle of the spot welded part using the lethargy coefficient obtained through the quasi-static tensile shear test for the specimen welded by current 10kA. The reliability evaluation of the life cycle is completed by comparing the life cycle calculated under the constant loading rate with the life cycle obtained by dynamic fatigue test. And then the result calculated by the lethargy coefficient is verified through the lift cycle calculated using the dynamic final tensile stress formula under the increased loading speed. This way can make save the time and cost in processing of predicting the life cycle of a structure.