• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.10a
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• pp.194-197
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• 1996

The high-strength aluminum alloy 7075-T651 was used to observe the fatigue-crack-propagation behavior for the various stress ratios with constant amplitude loading and thus to predict the fatigue life. With a chevron notch in the specimen the fatigue-crack-propagation behavior of through crack was investigated. Crack propagation behavior of through crack in the depth direction and crack growth of weldments were experimentally studied. Base material heat affected zone and weld material were considered in the fracture of weldments. The change of crack-propagation length with respect to several parameters such as stress intensity factor range(ΔK) effective stress intensity factor range(ΔKeff)ration of effective stress intensity factor range(U) stress intensity factor of crack opening point(K op) maximum stress intensity factor(K max) and number of cycles(Nf)was determined. The crack length of through crack of weldments was 2.4mm and the remaining part was a base material. The experiment was accomplished by making the crack propagate near the base material.

• Journal of Welding and Joining
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• v.18 no.5
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• pp.33-40
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• 2000

Fatigue crack propagation life of weld toe crack through residual stress field was estimated with Elber's crack concept. Propagation of weld toe crack is heavily influenced by residual stress caused by welding process, so it is essential to take into account the effect of residual stress on the propagation life of weld toe crack. Fatigue crack at transverse and longitudinal weld toe was studied respectively, which represent typical weld joint in ship structure. Numerical and experimental studies are performed for both cases. Residual stress near weldment was estimated through nonlinear thermo-elasto-plastic finite element method, and residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated with Newman-Forman-de Koning-Henriksen equation which is based on Dugdale strip yield model in estimating crack closure level U at different stress ratio. Calculated crack propagation life coincided well with experimental results.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.171-173
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• 2005

To evaluate the applicability of dissimilar metal friction stir welding in automobile manufacturing process, friction stir welding trials were carried out for typical 5000 and 6000 series aluminum alloy sheets with 2mm thickness. The sound joints of A15052 and A16061-T6 alloys were successfully formed under a wide range of welding condition. Excellent weld ability has been obtained at a condition of rotating speed 2000rpm and travel speed 100mm/min, while a radiographic test also confirmed defect free joint for this condition. Through the Erichsen cup test, the plastic formability of the FSWelded joints was found to be about 83% of base metal.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.174-176
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• 2005

On the basis of successful experiences and data from author's past experimental results of friction stir welding on thin aluminum plates, thick aluminum plate of high strength 2000 series has been carried out in this study. For various combination of rotating speed, welding speed and tool (RIWRC38-C) shape, the butt welded specimens has been prepared to check the metallurgical characteristics, hardness distributions and defects. From the results, feasible welding conditions have been obtained as 450 rpm rotating speed and 5 mm/min welding speed. Using these optimum welding parameters, 38.1mm-thickness A2519-T87 plates have been FSWelded in single pass. A good weld surface appearance and defects free weld zone has been observed in X-ray inspection. Softened region has been generated by dissolution of precipitates and coarsened microstructure in the stir zone after FSWeld.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.239-241
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• 2004

Stress intensity factor of semi-circular crack front was calculated by FEM, and also allowable crack size which doesn‘t break out the fracture by SCC in residual stress field of STS materials. Allowable crack size was increased with compressive residual stress provided by shot peening on material surface, and with magnitude of compressive residual stress for depth direction.

• Proceedings of the KSR Conference
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• 2000.05a
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• pp.242-249
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• 2000

The fatigue strength of welded aluminum alloy component has been evaluated. Extruded aluminum alloy component Al 6005-T6 was considered. That component could be one of appropriate candidates for floor structure in railway cars. Finite element analysis has been performed to obtain stress distribution in the welded aluminum component. The results of finite element analysis have been applied in designing the experimental setup for fatigue strength evaluation of welded component. Three point bending fatigue test has been employed, until fracture occurs, to evaluate the fatigue strength of the welded component. In addition, the fatigue strength of the component has been compared with that of specimen.

• 제어로봇시스템학회:학술대회논문집
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• 1989.10a
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• pp.322-326
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• 1989

This paper describes design procedure of suboptimal control to minimize a performance index which is represented as sum of square output error and the heat input power in arc welding process. Heat input and temperature of a fixed point on the surface of the material are concerned as input and output of the process, repectively. The suboptimal control law considered here in is a proportional plus integral type and is implemented by using only the output variables available from sensor which is also optimally located in a fixed point w.r.t. a moving weld touch.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.125-126
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• 2009

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.158-162
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• 2003

A study on friction welding of chrome molybedenum steel(SCM440) to carbon steel(S45C) is examined experimentally through tensile test, hardness test. So, this paper deals with optimizing the welding conditions and analyzing various mechanical properties about friction welds of SCM440 to S45C steel. The tensile strength of the friction welded joint was increased up to 100% of the S45C base matal under the condition of all heating time. Optimal welding conditions were n=2,000(rpm), $P_{1}=60(MPa)$, $P_{2}=100(MPa)$, $t_{1}=4(s)$, $t_{2}=5(s)$ when the total upset length is 5.7(mm).

• Journal of the Korean Society of Safety
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• v.29 no.6
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• pp.28-33
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• 2014

Vibro ripper worked by high frequency vibration is developed to do rock fragmentation and work of ripper is the different concept with other existing breakers. The gear box-shank welded joint of vibro ripper is very important part to deliver vibromotive force to tooth, so this part should endure high frequency vibration environments. The purposes of this study are to choose the optimal welding conditions for fatigue strength. The conditions were made using three kind of shank materials and two kind of filler metals. Shank materials are Hadox-hituf, Posten80 and AR400, and filler metals are CSF-71T and CSF-81T. The fatigue test was conducted each condition. Fracture surface was observed to estimate fracture characteristics of welded joint using SEM.