• Journal of Welding and Joining
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• v.26 no.2
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• pp.43-49
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• 2008

Fatigue cracks due to thermal stratification or corrosion in pipelines of nuclear power plants can cause serious problems on reactor cooling system. Therefore, the development of an integrated technology including fabrication of standard specimens and their practical usage is needed to enhance the reliability of nondestructive testing. The test material was austenitic STS 304, which is used as pipelines in the Reactor Coolant System of a nuclear power plants. The best condition for fabrication of thermal fatigue cracks at the notch plate was selected using the thermal stress analysis of ANSYS. The specimen was installed from the tensile tester and underwent continuos tension loads of 51,000N. Then, after the specimen was heated to $450^{\circ}C$ for 1 minute using HF induction heater, it was cooled to $20^{\circ}C$ in 1 minute using a mixture of dry ice and water. The initial crack was generated at 17,000 cycles, 560 hours later (1cycle/2min.) and the depth of the thermal fatigue crack reached about 40% of the thickness of the specimen at 22,000 cycles. As a results of optical microscope and SEM analysis, it is confirmed that fabricated thermal fatigue cracks have the same characteristics as real fatigue cracks in nuclear power plants. The crack shape and size were identified.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.124-132
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• 1999

Thermal fatigue strength of the solder joints is the most critical issue for TSOP(Thin Small Outline Package) because the leads of this package are extremely short and thermal deformation cannot be absorbed by the deflection of the lead. And the TSOP body can be subject to early fatigue failures in thermal cycle environments. This paper was discussed distribution of thermal stresses at near the joint between silicon chip and die pad and investigated their reliability of solder joints of TSOP with 42 alloy clad lead frame on printed circuit board through FEM and 3 different thermal cycling tests. It has been found that the stress concentration around the encapsulated edge structure for internal crack between the silicon chip and Cu alloy die pad. And using 42 alloy clad, The reliability of TSOP body was improved. In case of using 42 alloy clad die pad(t=0.03mm). $$\sigma$_{VMmax}$ is 69Mpa. It is showed that 15% improvement of the strength in the TSOP body in comparison with using Cu alloy die pad $($\sigma$_{VMmax}$=81MPa). In solder joint of TSOP, the maximum equivalent plastic strain and Von Mises stress concentrate on the heel of solder fillet and crack was initiated in it's region and propagated through the interface between lead and solder. Finally, the modified Manson-Coffin equation and relationship of the ratio of $N_{f}$ to nest(η) and cumulative fracture probability(f) with respect to the deviations of the 50% fracture probability life $(N_{f 50%})$ were achieved.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.323-330
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• 2008

High cycle bending fatigue of socket welded small bore pipe was characterized, and also the fatigue crack initiation of small bore pipe was monitored in situ by the acoustic emission (AE) technique. The STS 316L stainless steel specimens were prepared by gas tungsten arc welding (GTAW) process having the artificial defect (i.e., lack of penetration) and defect free at the root. The fatigue failure was occurred at the loc for high stress and root for relatively low stress. The crack initiation cycles ($N_i$) was defined to the abrupt increase in AE counts during the fatigue test, and then the cracks were observed by the radiographic test and electron microscope before and after the fatigue crack initiation cycles. The socket welded pipe damaged by bending fatigue was studied regarding the welding defect, failure mode, and crack initiation cycles for the diagnosis and monitoring.

• Journal of Welding and Joining
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• v.30 no.1
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• pp.64-71
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• 2012

The characteristics of high heat input (342kJ/cm) EG (Electro Gas Arc) welded joint of EH36-TM steel has been investigated. The weld metal microstructure consisted of fine acicular ferrite (AF), a little volume of polygonal ferrite (PF) and grain boundary ferrite (GBF). Charpy impact test results of the weld metal and heat affected zone (HAZ) met the requirement of classification rule (Min. 34J at $-20^{\circ}C$). In order to evaluate the relationship between the impact toughness property and the grain size of HAZ, the austenite grain size of HAZ was measured. The prior austenite grain size in Fusion line (F.L+0.1 mm) was about $350{\mu}m$. The grain size in F.L+1.5 mm was measured to be less than $30{\mu}m$ and this region was identified as being included in FGHAZ(Fine Grain HAZ). It is seen that as the austenite grain size decreases, the size of GBF, FSP (Ferrite Side Plate) become smaller and the impact toughness of HAZ increases. Therefore, the CGHAZ was considered to be area up to 1.3mm away from the fusion line. Results of TEM replica analysis for a welded joint implied that very small size ($0.8\sim1.2{\mu}m$) oxygen inclusions played a role of forming fine acicular ferrite in the weld metal. A large amount of (Ti, Mn, Al)xOy oxygen inclusions dispersed, and oxides density was measured to be 4,600-5,300 (ea/mm2). During the welding thermal cycle, the area near a fusion line was reheated to temperature exceeding $1400^{\circ}C$. However, the nitrides and carbides were not completely dissolved near the fusion line because of rapid heating and cooling rate. Instead, they might grow during the cooling process. TiC precipitates of about 50 ~ 100nm size dispersed near the fusion line.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.25 no.2
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• pp.87-104
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• 1989

Recently, with the tendency of more lightening, high-strength and high-speed in the marine industries such as marine structures, ships and chemical plants, the use of the aluminium Alloy is rapidly enlarge and there occurs much interest in the study of corrosion fatigue crack characteristics. In this paper, the initiation of surface crack and the propagation characteristics on the base metal and weld zone of 5086-H116 Aluminium Alloy Plate which is one of the Al-Mg serious alloy(A5000serious) used most when building the special vessels, were investigated by the plane bending corrosion fatigue under the environments of marine, air and applying cathodic protection. The effects of various specific resistances on the initiation, propagation behavior of corrosion fatigue crack and corrosion fatigue life in the base metal and heat affected zone were examined and its corrosion sensitivity was quantitatively obtained. The effects of corrosion on the crack depth in relation to the uniform surface crack length were also investigated. Also, the structural, mechanical and electro-chemical characteristics of the metal at the weld zone were inspected to verify the reasons of crack propagation behavior in the corrosion fatigue fracture. In addition, the effect of cathodic protection in the fracture surface of weld zone was examined fractographically by Scanning Electron Microscope(S.E.M.). The main results obtained are as follows; (1) The initial corrosion fatigue crack sensitibity under specific resistance of 25Ω.cm% show 2.22 in the base metal and 19.6 in the HEZ, and the sensitivity decreases as specific resistance increases (2) By removing reinforcement of weldment, the initiation and propagation of corrosion crack in the HAZ are delayed, and corrosion fatigue life increases. (3) As specific resistance decreases, the sensitivity difference of corrosion fatigue life in the base metal and HAZ is more susceptible than that of intial corrosion fatigue crack. (4) Experimental constant, m(Paris' rule) in the marine environment is in the range of about 3.69 to 4.26, and as specific resistance increases, thje magnitude of experimental constant, also increases and the effect by corrosion decreases. (5) Comparing surface crack length with crack depth, the crack depth toward the thickness of specimen in air is more deeply propagated than that in corrosion environment. (6) The propagation particulars of corrosion fatigue crack for HAZ under initial stress intensity factor range of $\Delta$k sub(li) =27.2kgf.mm super(-3/2) and stress ratio of R=0 shows the retardative phenomenon of crack propagation by the plastic deformation at crack tip. (7) Number of stress cycles to corrosion fatigue crack initiation of the base metal and the welding heat affected zone are delayed by the cathodic protection under the natural sea water. The cathodic protection effect for corrosion fatigue crack initiation is eminent when the protection potential is -1100 mV(SCE). (8) When the protection potential E=-1100 mV(SCE), the corrosion fatigue crack propagation of welding heat affected zone is more rapid than that of the case without protection, because of the microfissure caused by welding heat cycle.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.4 no.3
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• pp.183-188
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• 2003

Non-molding and welding line happen by the assembly of gas at the connector terminal. There is not good phenomenon of burr by increasing the over injection pressure, the temperatures of die and resin to prevent from them. Therefore, the connector mold to apply the vacuum molding system is developed in this study. The vacuum pressure is controlled systematically with the optimum conditions in the important ingredients of injection molding that are the temperatures of melting resin and die and cooling condition. The badness in charging is cleared by making a vacuum to non-charging part of the deep bottom part of each cavity. And the vacuum system to reduce the cycle time is applied as the study envelopment of molding work. So, the good product and the productivity improvement can be obtained in this study.

• Korean Journal of Computational Design and Engineering
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• v.9 no.1
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• pp.62-76
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• 2004

Many customers are no longer satisfied with mass-produced goods. They are demanding customization and rapid delivery of innovative products. Many companies are now realizing that the best way to reduce life cycle costs is to evolve a more effective product development paradigm using Internet and web based technologies. Yet there remains a gap between current market demands and product development paradigms. The existing CAD systems require that product developers possess all the design analysis tools in-house making it impractical to employ all the needed and newest tools. Hence, this paper addresses how assembly operation analysis can be embedded transparently and remotely into a service-oriented collaborative assembly design environment. A new assembly operation analysis framework is introduced and a relevant architecture and tools are developed to realize the framework. Instead of the current sequential process for verifying and validating an assembly design, a new Virtual Assembly Analysis (VAA) method is introduced in the paper to predict the various effects of joining during actual collaborative design. As a case study, arc welding and riveting processes are investigated. New service-oriented VAA architecture and its VAA components are proposed and implemented on prototype mechanical assemblies.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.2
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• pp.176-183
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• 2000

In this paper, sixth order hannonic injected PWM for improving‘ input CWTent distortion of single switch t three phase boost converter is presented. Peliodic sixth order hmmonic ${\gamma}$oltage is inj<:ded in the control circuit t to var${\gamma}$ the duty ratio of the converter switch within one switching cycle. In the result, the input phase c currents are forced to track the input voltage and an 해most unity power factor is obtained. Expelimental r results are verified by converter operating at 400V /6kW with three phase 140V ~220V input and by C02 arc w welding machine which was nonlinear load with 3 $\phi$ 220V input.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.814-819
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• 2005

The phase change heat transfer has been applied to the processes of machines as well as of manufacturing. The cycle in a heat exchanger includes the phase change phenomena of coolant for air conditioning, the solidification in casting process makes use of the characteristics of phase change of metal, and the welding also proceeds with melting and solidification. To predict the phase change processes, the experimental and numerical approaches are available. In the case of numerical analysis, the Enthalpy method is most widely applied to the phase change problem, comparing to the other numerical methods, i.e. the Equivalent Specific Heat method and the Temperature Recovery method. It's because that the Enthalpy method is accurate and straightforward. The Enthalpy method does not include any correction step while the correction of final temperature field is inevitable in the Equivalent Specific Heat method and the Temperature Recovery method. When the temperature field is to be used in the calculation, however, there must be converting process from enthalpy to temperature in the calculation scheme of Enthalpy method. In this study, an improved method for the Equivalent Specific Heat method is introduced whose method dose not include the correction steps and takes temperature as an independent variable so that the converting between enthalpy and temperature does not need any more. The improved method is applied to the solidification process of pure metal to see the differences of conventional and improved methods.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.79-81
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• 2005

Bridges constructed recently are preferred to have long spans and simple structure details considering not only the function as bridge but scenic beauty, maintenance, construction term and life cycle cost, etc. Therefore, they require high performance steels like extra-thick plate steels and TMCP steels. A TMCP steel produced by themo-mechanical control process is now spot lighted due to the weldability for less carbon equivalent. It improved at strength and toughness in microstructure. Recently, the SM570-TMC steel which is a high strength TMCP steel whose tensile strength is 600MPa has been developed and applied to steel structures. But, for the application of this steel to steel structures, it is necessary to elucidate not only the material characteristics but also the mechanical characteristic of welded joints. In this study, the characteristics of residual stresses in welded joints of SM570-TMC steel were studied through the three-dimensional thermal elastic-plastic analyses on the basis of mechanical properties at high temperatures obtained from the elevated temperature tensile test.