• Korean Journal of Metals and Materials
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• v.48 no.3
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• pp.203-209
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• 2010

An application of the instrumented indentation technique has been expanded from the measurements of hardness and elastic modulus to the analysis of residual stress. A slope of the indentation loading curve increases (or decreases) according to compressive (or tensile) residual stress. A theoretical equation has been established for quantifying residual stress from the slope change. However, a precise observation of the remnant indents is indispensible because the theoretical approach needs actual contact information. In addition, the conventional hardness test is still used for predicting the residual stress distribution of welded joints. Thus, we observed the three-dimensional morphologies of the remnant indents formed on artificial stress states and analyzed stress effects on morphological recovery of the indents. First, a depth recovery ratio, which has been regarded as a sensitive stress indicator, did not show a clear dependency with the residual stress. Thus an analysis on volumetric recovery was tried in this study and yielded a inverse proportional behavior with the residual stress. In addition, an elastic to plastic volume recovery ratio showed more significant correlation with the residual stress.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.42-46
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• 2016

Hydrogen assisted cracking (HAC) is one of the most complicated problem in welding. Huge amount of studies have been done for decades. Based on them, various standards have been established to avoid HAC. But it is still a chronic problem in industrial field. It is well known that the main causes of the hydrogen crack are residual stress, crack susceptible micro structures and a certain critical level of hydrogen concentration. Even though the exact generating mechanism is unclear till today, it has been reported that the hydrogen level in the weld metal should be managed less than a certain amount to prevent it. Matsuda studied that the residual hydrogen level in the weld metal can be varied even if the initial hydrogen content is same. It is also insisted in this report that the residual hydrogen concentration is in stronger correlation with hydrogen crack than the initial hydrogen content. But, in practical point of view, the residual hydrogen is still hard to consider because measuring hydrogen level is time and cost consuming process. In this regard, numerical analysis is the only solution for considering the residual hydrogen content. Meanwhile, Takahashi showed the possibility of predicting the residual hydrogen by a rigorous FE analysis. But, few commercial software suitable for solving the weld metal hydrogen has been reported yet. In this study, two dimensional thermal - hydrogen coupled analysis was developed by using the commercial FE software MARC. Since the governing equation of the hydrogen diffusion is similar to the heat transfer, it is shown that the heat transfer FE analysis in association with hydrogen diffusion property can be used for hydrogen diffusion analysis. A series of simulation was performed to verify the accuracy of the model. For BOP (Bead-On-Plate) and the multi-pass butt welding simulations, remaining hydrogen contents in the weld metal is well matched with measurements which are referred from Kim and Masamitsu.

• Journal of Welding and Joining
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• v.24 no.2
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• pp.48-56
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• 2006

The fatigue strength of the welds is affected by such factors as the weld geometry, microstructures, tensile properties and residual stresses caused by fabrication. It is very important to evaluate the structural integrity of the welds in nuclear power plant because the weldment undergoes the most of damage and failure mechanisms. In this study, the fatigue assessments for a reactor vessel outlet nozzle with the weldment to the piping system are performed considering the welding residual stresses as well as the effect of local brittle zone in the vicinity of the weld fusion line. The analytical approaches employed are the microstructure and mechanical properties prediction by semi-analytical method, the thermal and stress analysis including the welding residual stress analysis by finite element method, the fatigue life assessment by following the ASME Code rules. The calculated results of cumulative usage factors(CUF) are compared for cases of the elastic and elasto-plastic analysis, and with or without residual stress and local brittle zone effects, respectively. Finally, the fatigue life of reactor vessel outlet nozzle weld is slightly affected by the local brittle zone and welding residual stresses.

• Fibers and Polymers
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• v.2 no.4
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• pp.203-211
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• 2001

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait\`s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.84-89
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• 1999

Most of ferrous b.c.c weld materials may experience martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is a prerequisite to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions. i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. consequently, in this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.6
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• pp.50-56
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• 2006

Residual gas fraction in a combustion process is very crucial to improve combustion and cyclic variations. Especially, the residual gas fraction is strongly affected by backflow of the residual gas during the valve overlap period in an idle operation. Therefore, it is one of the most interesting that valve timings can affect flow characteristics of gas exchange process, especially during idle operation. This analysis investigates residual gas fraction with respect to valve timing changes which is critical for combustion efficiency and engine performance. Flow characteristics of residual gas by changing intake and exhaust valve timing are calculated by CFD methodology during an idle operation in an SI engine. It is analyzed that retarded EVO and advanced IVO results in the increase of valve overlap period and consequently, residual gas fraction. Futhermore, changes in IVO have stronger effects on variation of residual gas fraction.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.17
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• pp.7383-7387
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• 2014

Background: To determine rates of residual disease along with influencing factors in women with stage IA to IB1 cervical carcinoma after conization. Materials and Methods: A retrospective study was conducted of medical records of 198 stage IA to IB1 cervical carcinoma patients who had undergoing cervical conization followed by primary surgical treatment during 2006-2013. Independent factors correlating with residual carcinoma in subsequent surgical specimens were analyzed by stepwise regression analysis. Results: Mean age was 48.9 years. Cone specimens demonstrated free margins in 36 women (18.8%). In case of having disease at margin, high-grade cervical intraepithelial neoplasia (CIN) and carcinoma were evidenced in 58 and 97 women, respectively. Pathology of subsequent specimens revealed residual carcinoma in 78 women (39.4%), high-grade CIN or adenocarcinoma in situ (AIS) in 45 (22.7%), and no residual pathology in 75 (37.9%). Age more than 35 years, postmenopausal status, having symptoms, diseases or invasive lesions at conization margins or disease on endocervical aspect, and higher stage were significantly correlated with residual cancer in surgical treatment specimens. On regression analysis, postmenopause and stage were independent factors associated with residual carcinoma.Conclusions: Patient and tumor characteristics are predictive factors for residual cancer in the studied group of women.

• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.35-41
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• 2000

Residual stress is defined as a minimum stress with a large displacement of specimens and the residual stress after peak shear stress appears with displacement volume but there is no provision to select the residual stress. In the previous study, residual stress was recorded when the change of shear load is small in the condition of the strain more than 15%. But, in this study, hyperbolic function((No Abstract.see full/text), b=experimental constant) of soil test is adapted to joint of rock and the propriety is investigated. In a landslide and landsliding of artificial slope, wedge failure of tunnel with a large displacement, tests are simulated from peak stress to residual stress for safety analysis. But now. direct shear stress and triaxial compressive tests are usually performed to find out characteristics of shear stress about joint. Although these tests get a small displacement, that data of peak stress and residual stress are used for safety analysis. In this study, we tried to determine failure criteria for joints of rock using ring shear test machine. The residual stress following shear behavior was determined by the result of ring shear test and direct shear test. In conclusion, after comparing the results of the two test, we found that cohesion(c) and internal friction angle(ø) of ring shear test are 30% and 22% respectively of those of the direct shear test.

• Journal of the Korean Society of Safety
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• v.20 no.3 s.71
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• pp.34-41
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• 2005

For assessing residual lift of the steam pipe in fossil power plants, inspections and analysis are usually focused on the critical locations such as butt welds, elbows, Y-piece and T-piece of the steam pipes. In predicting the residual life of T-piece, determination of local stress near welds considering system load as well as internal pressure is not a simple problem. In this study, stress analysis of a T-piece pipe was conducted using a three-dimensional model which represents the T-piece of a domestic fossil power station. Elastic and elastic-creep analysis showed the maximum stress level and its location. Residual creep rupture life was also calculated using the stress analysis results. It was argued that the calculated life is reasonably same as the measured one. The stress analysis results also support life prediction methodology based on in-field replication technique.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.61-63
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• 2001

Residual stress distribution in injection-molded short fiber composites was determined using layer-removal method. Polysterene with 3 vol% carbon fibers was injection-molded into the tensile specimen. With milling machine layer-removal process was conducted and the curvature data were acquired. Treuting and Read analysis which is assuming isotropic material, and White analysis considering anisotropy due to the fiber orientation were used to calculate residual stress of the flow direction through the thickness direction and compared with each other.