• Proceedings of the KSR Conference
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• 2004.06a
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• pp.878-882
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• 2004

We investigated the effect of weld details on fatigue behavior of a material, JIS SM 490 A, with yielding strength of about 350 MPa and tensile strength of about 520 MPa. Tensile tests, instrumented indentation tests and fatigue tests were carried out on double V-grooved butt weld plates such as reinforcement removed, as-welded and weld toe ground. In addition plates with transverse fillet welded web, load carrying cruciform fillet welded plates, non-load-carrying cruciform fillet welded plates, longitudinal butt welded plates and welded rectangular life-size box beams were tested. S-N curves for the above specimens were obtained and analyzed.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.359-364
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• 2004

We investigated the effect of weld details on fatigue behavior of a material, JIS SM 490 A, with yielding strength of about 350 MPa and tensile strength of about 520 MPa. Tensile tests, instrumented indentation tests and fatigue tests were carried out on double V-grooved butt weld plates such as reinforcement removed, as-welded and weld toe ground. In addition plates with transverse fillet welded web, load carrying cruciform fillet welded plates, non-load-carrying cruciform fillet welded plates and longitudinal butt welded plates were tested. S-N curves for the above specimens were obtained and analyzed

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.165-172
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• 2013

Power generating unit structures are designed and built to meet standard to secure its safety for expected life time. As the structures have been exposed to combined environment, degradation of structure material is accelerated and it can cause unexpected damage; evaluating precise mechanical properties of weak site like welded area is an essential research area as it is directly connected to safety issues. Existing measuring technique like tensile test requires specific size in testing specimen yet it is destructive method which is hard to apply on running structures. To overcome above mentioned limitation, IIT is getting limelight as it is non-destructive and simple method. In this study, latest technique is introduced to evaluate tensile property and residual stress by analyzing stress field occurs under the indenter while IIT is performed. Test on welded area, the weak site of nuclear structures have been practiced and confirmed that IIT can be usefully applied to evaluate integrity in industry.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.1
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• pp.35-42
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• 2008

Instrumented sharp indentation test is a well-directed method to measure hardness and elastic modulus. The sharp indenter such as Berkovich and conical indenters have a geometrical self-similarity in theory, but the self-similarity ceases to work in practice due to inevitable indenter tip-blunting. In this study we analyzed the load-depth curves of conical indenter with finite tip-radius via finite element method. Using the numerical regression data obtained from Kick's law, we first confirmed that loading curvature is significantly affected by tip radius as well as material properties. We then established a new method to evaluate Young's modulus, which successfully provides the value of elastic modulus with an average error of less than 2%, regardless of tip-radius and material properties of both indenter and specimen.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.40-46
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• 2015

This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.

• Proceedings of the Korean Reliability Society Conference
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• 2011.06a
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• pp.125-130
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• 2011

발전 설비는 기대 수명동안의 안정성을 확보하기 위하여 해당 규격에 부합하도록 설계하여 건설된다. 하지만 가동 중 다양한 복합 환경에 노출됨에 따라 구조물을 이루고 있는 재료의 열화 현상이 가속화되어 예기치 못한 파손이 발생할 수 있다. 기계적 물성은 재료의 기계적 거동을 나타내는 주요 척도가 되며 이는 신뢰성 및 안전과 직결된다. 하지만 기존의 역학물성을 측정하는 대부분의 시험법들은 특정 크기의 시편을 요구하고 파괴적인 시험법이기 때문에 가동 중 시설물에 적용하기가 불가능하였다. 이러한 한계점을 극복하고자 비파괴적이고 정량적인 시험이 가능한 연속압입시험법이 최근 각광받는 시험법으로서 많은 연구자들에 의해 연구되고 있다. 이 시험법은 시험 대상물의 형상에 제약을 받지 않으며 시험 절차가 매우 간단하다는 장점을 가진다. 또한 대상의 국소 부위에 시험할 수 있어 취약 부위 판별이 가능하다. 본 연구에서는 대표응력-대표변형률 기법을 통하여 인장물성을 평가하고, 압입 하중 차이를 이용하여 소재에 존재하는 잔류응력을 평가하는 기법을 소개한다. 또한, 연속압입시험을 이용하여 실제 발전소 파이프의 취약부위로 알려진 용접부에 대하여 인장물성 및 잔류응력을 측정함으로써 실제 산업체의 신뢰성 평가가 적용할 수 있음을 확인하였다.

• Journal of the Korean Society of Safety
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• v.32 no.5
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• pp.1-7
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• 2017

Forensic Engineering is the art and science of professionals qualified to serve as engineering experts in courts of law or in arbitration proceedings. Buses using compressed natural gas (CNG) trend to be extended in use internationally as optimal counterplan for reducing discharge gas of light oil due to high concern about environment. However, CNG buses is equipped with composite pressure vessels (CPVs); since the CPVs contain compressed natural gas, the risks in the case of accident is very high. In this study, the bursting test for the pressure vessel depending on the heat treatment conditions of the vessel in which the actual ruptured accident occurred, after the bursting test, the fracture pattern analysis had performed. The mechanical materials properties test using Instrumented Indentation Test had performed to confirm the mechanical properties for each heat treatment cases. Also, the fractography analysis and metallographic analysis had performed to find out the difference of each heat treatment case. By comparing normal vessel with abnormal vessel which have defect of heat treatment conditions in term of the bursting patterns and characteristics of containers using various forensic engineering methods, especially, it is possible to understand how important the heat treatment process is in the high pressure vessel unlike any product.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.7-13
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• 2012

A spacer grid which is one of the most important structural components in a pressurized water reactor fuel is an interconnected array of slotted grid straps, welded at the intersections to form an egg-crate structure. The spacer grid is required to not only protect fuel rods stably but also have sufficient lateral crush strength for the sake of enabling shut-down of the nuclear reactor during abnormal operating environments. Then, the lateral crush strength of the spacer grid is closely related with welding quality of the spacer grid. Previous research on the crush strength analysis of the spacer grid had been performed using only parent material properties. In this study, to investigate the effect on the crush strength of the spacer grid when used mechanical properties in weld zone instead of parent material properties, crush strength analysis considering mechanical properties in weld zone obtained from the instrumented indentation technique was performed and compared the results with the previous research.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.61-66
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• 2010

A virtual manufacturing system that is composed of JMatPro, a material modeler and $DEFORM^{TM}$-HT, a finite element package is applied to the hot press forming process: high temperature material properties for each phase such as flow stress, elastic modulus, Poisson's ratio, thermal expansion coefficient, in addition to TTT curve are predicted by JMatPro and taken into $DEFORM^{TM}$-HT to predict the material behavior considering phase transformation and heat transfer simultaneously. In order to verify the accuracy of computation, the residual stress and the springback were compared with the experimental measurements. Both the predicted and measured principal residual stresses and amount of springback were in good agreement. It was also found that the residual stresses generated from hot press forming are not negligible as it has been generally assumed, although the springback deformation is quite small.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.1
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• pp.9-16
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• 2011

Primary water stress corrosion cracking (PWSCC) has been found in the weld region of the nuclear power plant. Welding can produce tensile residual stress. Tensile residual stress contributes to the initiation and growth of PWSCC. It is important to estimate weld residual stress accurately to predict or prevent the initiation and growth of PWSCC. This paper shows the results of finite element analysis and measurement experiment for weld residual stress. For the study, four kinds of specimen were fabricated with the materials used in the nuclear power plant. Residual stresses were measured by four kinds of methods of hole drilling, x-ray diffraction, instrumented indentation and sectioning. Through the study, numerical analysis and measurement results were compared and the characteristics of each measurement technique were observed.