• 한국안전학회지
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• 제21권5호
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• pp.17-21
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• 2006

In this study, SPCC cross-tension type specimens produced under various spot welding conditions were tensile and fatigue tested. Decrease of 2 kA in normal current condition of 10 kA caused a large amount of reduction in both static joining strength and fatigue life. And 2 kA increase resulted in increase of static joining strength and an increase in low cycle regime but a decrease in high cycle regime, revealing the fact that fatigue strength rather than static joining strength would be a major factor during design process in view of the body endurance. As a results of estimating the fatigue lifetimes of various types of spot weld specimens. equivalent stress intensity factor is the proper parameter for predicting the lifetimes of various types of specimens. which can be expressed as ${\Delta}K_{eq}(N/nm^{1.5})=11550N^{-0.36}_{f}$.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.675-680
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• 2006

This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter-or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses.

• Journal of Welding and Joining
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• 제11권4호
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• pp.79-90
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• 1993

Shielded metal arc welding, one-ploe and two-pole submerged arc welding were accomplished to investigate microstructure changes on phase transformation behavior in $60kg/mm^2$ quenched and tempered high strength steel. Microstructures were examined by optical micrograph and TEM. In shielded metal arc welding (oxygen 250ppm), the inclusions were small size (0.3-0.5$\mu\textrm{m}$)and small in number. In submerged arc welding (oxygen 430-529ppm), the inclusions were larger(0.7-2$\mu\textrm{m}$) than that of shielded metal arc welding and large in number. Microstructure mainly depends on number and distribution of inclusions in fusion zone of weld metal. It was noticed that a limited number of inclusions favors the formation of acicular ferrite.

• Journal of Advanced Marine Engineering and Technology
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• 제21권5호
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• pp.542-548
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• 1997

In this study an evaluation method of fatigue strength of membrane type LNG tank is presented with FEM analysis and experimental approach of seam and raised edge welds. The study contains the following : l)FEM analysis of test specimens 2)Fatigue tests of seam and raised edge welds 3)Estimation of cumulative damage factor of the welds on the basis of safe life design concept complying with the rules of classification society 4)Review of the effect of mean stress on the fatigue strength 5)Modelling of fatigue life of the welds which is changeable by weld heights With the results obtained in this study, a model ${\Delta}{\delta}/h^2=0.13553\;{N_{f}}^{-0.3151}$ for seam and raised edge welds having a given weld height is proposed to be useful for designers and inspectors.

• Design & Manufacturing
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• 제14권2호
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• pp.42-48
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• 2020

This study is on the injection molding analysis for the LED outdoor lighting top cover of one heat sink body type structure. Thermoplastic and thermosetting resins were applied to compare the thermal properties during the injection molding process. The thermoplastic resin is used in this study due to special characteristics that it is light, good strength and dose long not transmute quality even if pass long time. The thermosetting resin is applied to this study due to good in strength, lightweight and excellent etc, thermal conductivity. This study presented a preliminary analysis of fill time, weld line, air trap etc. for the injection molding process of LED lamp cover and body through simulation using Moldflow. As a result of the study, it was selected HTM-102 material because the thermosetting resin has excellent strength and heat conductivity.

• Journal of Welding and Joining
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• 제13권4호
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• pp.103-112
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• 1995

This study was performed to optimize friction welding conditions of Cr-Mo steel bars used for hydraulic of pneumatic valve spools and to realize the real-time evaluation of weld quality by acoustic emission method. SNCM220, SCM435, SCAM645, and SCM415 steel bars were tested to find optimum conditions of friction welding. Auantitative equations which exhibit the relations of tensile strength, elongation, reduction of area and energy absorption with friction heating time were obtained by the experiment. Acoustic emission was also performed in the friction weldig process, and the real-time evaluation was enabled to find the optimum range of weld strength. Finally, the strength and toughness of welded joints were interpreted by the sem analysis of tensile fracture surfaces.

• Journal of Welding and Joining
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• 제15권5호
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• pp.115-123
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• 1997

The buckling strength, fatigue strength, stress corrosion cracking are considerably effected on one of initial imperfections, the residual stresses produced by a circumferential weld between axisymmetric cylinders. Therefore, we study the residual stresses, plastic strain and temperature distribution with using thermal elasto-plastic analysis which are generated by a circumferential weld between axisymmetric cylinders. It is investigated that welding residual stresses have an effect on the strength of cylinder for inner and outer shell under external pressure.

• 한국강구조학회 논문집
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• 제10권4호통권37호
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• pp.779-788
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• 1998

본 논문은 강교량 부재에 번번하게 사용되는 용접상세로 비교적 낮은 피로강도를 보이는 부재에 대해 실험과 해석적 연구를 수행하였다. 측정응력을 고려해보면, 피로균열은 복부에 연결되는 거셋판의 필렛용접 지단부에서 시작하였으며, 용접단면의 기하학적 조건과 불연속성으로 인하여 집중응력이 발생하는 것으로 나타났다. 비드단면의 기하학적 형상을 고려한 FEM 모델의 해석결과와 동일한 위치에서 게이지에 의한 측정응력은 둘다 비슷한 수준의 응력집중이 용접지단부에서 발생하고 있음을 보여주고 있다. 피로실험 결과를 AASHTO와 JSSC의 피로설계기준과 비교한 결과, 80mm와 150mm 부착 시험편 모두에서 AASHTO의 D와 E등급, JSSC의 F와 G등급을 만족하거나 상회하는 것으로 나타났다. 또한, WG1와 WG3 시험편은 AASHTO와 JSSC의 S-N선도 보다 완만한 -0.3의 기울기를 갖는 것으로 나타났다.

• Journal of Welding and Joining
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• 제32권5호
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• pp.44-49
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• 2014

The effect of weldbond hybrid joining process on the mechanical behavior of single lap and L-tensile joints was investigated for the newly developed 1.2GPa grade ultra high strength TRIP(transformation induced plasticity) steel. In the case of single lap shear behavior, the weldbond joint of 1.2GPa TRIP steel showed lower maximum tensile load and elongation than that of the adhesive bonding only. It was considered to be due to the reduction of real adhesion area, which was caused by the degradation of adhesive near the spot weld, and the brittle fracture behavior of the spot weld joint. In the case of L-tensile behavior, however, the maximum tensile load of the weldbond joint of 1.2GPa TRIP steel was dramatically increased and the fracture mode was change to the base metal fracture which is desirable for the spot weld joint. These synergic effect of the weldbond hybrid joining process in 1.2GPa TRIP steel was considered to be due to the stress dissipation around the spot weld joint by the presence of adhesive which resulted in the change of crack propagation path.

• 한국기계가공학회지
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• 제2권4호
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• pp.53-60
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• 2003

Large sized marine structures are used under corrosion environment of seawater and applied by severe service loading such as an ocean current, a billow and a tempest. Marine structures are usually constructed by lots of thick wall steel pipes joining welded joints. The thickness of such as steel pipes is usually more than 40mm. The such as steels are called "Thermo-Mechanical Control Process steel (TMCP steel)" strengthened by a heat treatment in process of steel manufactures. The failure, especially crack initiation, of marine structures was starting at weld joints under service condition. Then they should be designed by basis of the fatigue strength under seawater corrosion environment of weld joints. To clarity the fatigue crack initiation behavior is important more than to clarify the crack propagation behavior on the strength design of marine structures, because it is very difficult to find out the crack initiation and propagation phenomena and then even if it will be able to find out, it is considered that the refit of the damaged parts of welded joints have a technical difficulty under the sea. Therefore, it is most important to clarify the corrosion fatigue crack initiation behavior under the seawater condition. But, there is one big difficulty to make a test for thick plate specimen, for example thicker than 40mm. Because, it is need large capacity loading apparatus to test such as thick plate specimen. In this research, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the fatigue clack initiation tests with relatively low cyclic loading and to observe a fatigue crack initiation behavior.