• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.705-710
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• 2002

Welding is used not only during the shipbuilding, but also during the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, The result within identical materials showed that the heat-affected zone was slower than that of parent metal

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.11-24
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• 1998

The invention of fusion wilding technology has brought on a revolutionary change in manufacturing industry which enables the construction of large scale high temperature plants in chemical, petrochemical and power generation industries. However, among the failure cases of high temperature components, premature failures of weldments have taken a large percentage that indicates the detrimental effect of welding on structural integrity. The accurate prediction of the high temperature behaviour of welded components is thus becoming increasingly important in order to realise an optimised design and maintenance of a plant life. In the present paper, recent research activities on high temperature behaviour of welded structures are briefly summarised. A local deformation measuring technique is proposed to determine the creep properties of weldment constituents. A damage mechanics approach is introduced to study the life reduction and ductility reduction due to the presence of a weld in high temperature structures. Finally, the high temperature creep crack growth in weldments is discussed.

• International Journal of Korean Welding Society
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• v.5 no.1
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• pp.53-59
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• 2005

Auto industry has employed resistance spot welding(RSW) to join steel sheets for structural rigidity of automobile body. Driven by the need to reduce weight and fuel consumption, car companies have been evaluating aluminum intensive vehicles(AIVs) as a way to reduce vehicle weight without downsizing. During the transition from all steel-construction vehicle body to aluminum intensive body, joining aluminum to steel sheets emerges as a serious contender in automobile body. This paper deals with application of transition material to RSW aluminum to steel. Placing transition material insert between the aluminum/steel interface was found very effective to overcome physical incompatibility between aluminum and steel. Use of transition insert allows for two separate weld nuggets to be formed in their respective aluminum/aluminum and steel/steel interfaces. This RSW processes was monitored with the aid of dynamic resistance sampling. Typical patterns in sampled dynamic resistance curves indicated formation of sound nugget. The growth of two separate nuggets was examined by micro-cross section test.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.3
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• pp.181-189
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• 2001

For the Tailor Welded Blank sheet used fur automobile body panel, the characteristics of fatigue crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9+0.9mm) and different (0.9+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The crack propagation rate was noticeably decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness. Elasto-Plastic analysis was performed by finite element analysis fur explaining the test results.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.276-281
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• 2002

A metallurgical model for bainite transformation kinetics in the coarse-grained heat affected zone(CGHAZ) on the basis of an Avrami-type equation was studied. Isothermal transformation tests were carried out to obtain the empirical equations for incubation time and Avrami kinetic constants for C-Mn-Mo-Ni steel. The effect of prior austenite grain size(PAGS) on the reaction rate of bainite was also investigated. Compared with experimental transformation behavior of bainite, the predicted behavior was in good agreement. It was also found that a smaller grain size retard the bainite reaction rate, contrary to the classical grain size effect and this is considered to be caused by constraint of grain size to bainite growth.

• 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.

• Nuclear Engineering and Technology
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• v.44 no.8
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• pp.961-970
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• 2012

Often, probabilistic fracture mechanics (PFM) approaches have been adopted to quantify the failure probabilities of Ni-base alloy components, especially due to primary water stress corrosion cracking (PWSCC), in a primary piping system of pressurized water reactors. In this paper, the key features of an advanced PFM code, PINEP-PWSCC (Probabilistic INtegrity Evaluation for nuclear Piping-PWSCC) for such purpose, are described. In developing the code, we adopted most recent research results and advanced models in calculation modules such as PWSCC crack initiation and growth models, a performance-based probability of detection (POD) model for Ni-base alloy welds, and so on. To verify the code, the failure probabilities for various Alloy 182 welds locations were evaluated and compared with field experience and other PFM codes. Finally, the effects of pre-existing crack, weld repair, and POD models on failure probability were evaluated to demonstrate the applicability of PINEP-PWSCC.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.24-30
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• 1990

2024 Aluminium was welded by domestic manufactured continuous type friction welder. The problems and optimum condition were studied in 2024 Al-2024 Al cases. Mechanical tests and microstructure analysis were studeid. Interfacial temperature of welding was predicted by FDM. The obtained results are as follows: 1) In case of Al-Al, the optimum condition range was wide. 2) At the boundary zone, fine recrystallized zone was not harmful to the mechanical property and no growth of precipitation was observed. 3) In case of Al-Al, temperature gradient can be predictedby FDM and heat input can be taken as weld parameter.

• Journal of Welding and Joining
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• v.11 no.1
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• pp.2-8
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• 1993

A literature review was conducted to gather informations available on the welding metallurgy of aluminum alloys, emphasized on characteristics in the heat affected zone(HAZ). Nominal metallurgical reactions that occur in aluminum alloys provide a basis for understanding aluminum welding metallurgy. However, welding reactions differ to some extent because of the relatively short times involved, and the non-isothermal heating excursed. For non-heat treatable alloys, welding primarily affects these alloys by annealing (recrystallization and growth) and to a less extent, changes in low temperature precipitates. In the case of heat treatable alloys, the resulting HAZ properties depend upon alloy composition, starting temper, heat input and post weld heat treatments.

• Proceedings of the KWS Conference
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• 1996.05a
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• pp.115-118
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• 1996

1. The crack is inifiated at a toe notch and reptured for the skip and continuous welding. 2. Fatigue life of continuous welding is greater than that of skip welding and fatigue life of 2pad continuous welding appears 1.7 times more than that of pad continuous welding. 3. For the skip and continuous welding, fatigue than that of welding materials appears shorter than that of welding materials because of the effect of plastic strain and compressive residual stresses at the crack tip, which are generated by the over loading. 4. Inter-relationship between da/dN-ΔK and delayed phenomenon increases linearly at the state growth area of heat effect section for the skip and continuous welding.