• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.47-56
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• 1993

Typical plastic strains in the machined surface are very difficult to measure, since they are located within a very short distance from the surface and they change very rapidly. There is an alternative way to determine the residual strain in plastically deformed materials by measuring the grain size after a subsequent recrystallization precess. Although, this technique has been successfully applied by several researchers to find the plastic zone around notches and cracks in various materials and welding beads, few works have been reported using the recrystallization method to determine the residual strains in machined surface. Therefore, the purpose of this investigation is to explore the effectiveness of the recrystallization technique in machining applications and in particular, to find the effect of cutting parameters, i.e., depth of cut, rake angle, on the plastic strains. As the result, the recrystallization technique was succesfully applid to determine the plastic strain in machined surface.

• Structural Engineering and Mechanics
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• v.11 no.5
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• pp.565-574
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• 2001

Experimental investigation into the behaviour of half-scale brick masonry panels were conducted under cyclic loading normal to the bed joint and parallel to the bed joint. For each cycle, full reloading was performed with the cycle peaks coinciding approximately with the envelope curve. Unloading, however, was carried out fully to zero stress level and partially to two different stress levels of 25 percent and 50 percent of peak stress. Stability point limit exhibits a unique stress-strain curve for full unloading but it could not be established for partial unloading. Common point limit was established for all unloading-reloading patterns considered, but its location depends on the stress level at which unloading is carried to. Common point curves were found to follow an exponential formula, while residual strains versus envelope strains can be expressed by a polynomial function of a single term. The relation between residual strain and envelope strain can be used to determine the stress level at which deterioration due to cyclic loading began.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.67-72
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• 2008

The objective of this study is to design a laboratory specimen for simulating residual stress of circumferential butt welding of pipe. Specimen type and method for residual stress generation were proposed based on the review of prior studies and parametric finite element simulation. To prove the proposed specimen type and loading method, the residual stress was generated using the designed specimen by applying proposed method and was measured. The measured residual stress using X-ray diffraction reasonably agreed with the results of finite element simulation considered in the specimen design. Comparison of residual strains measured at several locations of specimen and given by finite element simulation also showed good agreement. Therefore, it is indicated that the designed specimen can reasonably simulate the residual stress of circumferential butt welding of pipe.

• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.7-13
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• 2009

The objective of this study is to design a laboratory specimen for simulating residual stress of circumferential butt welding between pipes. Specimen type and method to generate residual stress were proposed based on the review of prior studies and parametric finite element analysis. To prove the proposed specimen type and loading method, the residual stress was generated using the designed specimen by applying proposed method and was measured. The measured residual stress using X-ray diffraction reasonably agreed with the results of finite element analysis considered in the specimen design. Comparison of residual strains measured at several locations on the specimen and given by finite element simulation also showed good agreement. Therefore, it is indicated that the designed specimen in this study can reasonably simulate the axial residual stress of a circumferential butt welding of pipe.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.156-158
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• 2003

Sheets of aluminum alloy 1050 were asymmetrically cold rolled in a rolling mill with different roll speeds. In order to promote the shear deformation during asymmetrical rolling, cold rolling without lubrication was performed. The variation of the shear strain state during asymmetrical rolling was tackled by means of FEM calculations. Asymmetrical rolling gave rise to the development of pronounced residual shear strain gradients throughout the thickness layers.

• Microbiology and Biotechnology Letters
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• v.28 no.6
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• pp.309-315
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• 2000

To isolate yeast strains producing high concentration of ethanol, 125 strains were subjected to screening. Initially 14 strains able to grow in a medium containing 15%(v/v) ethanol, 7 strains capable of growing in a medium containing 50%(v/v) glucose, 23 strains having relatively fast fermentation rates, 13 strains able to grow at $42^{\circ}C$ were selected. After secondary screening, 11 strains having relatively high ini-tial fermentation rate and producing high concentration of ethanol were selected. After tertiary screening 5 strains producing high concentration of ethanol were selected. These 5 strains were again for their ethanol produc-tion, residual sugar, and viability using fermentation medium containing 25% glucose. The strain producing the highest concentration of ethanol was 20-1 strain which produced 10.56%(v/v) ethanol in 4 days, and the highest viable strain was 11-1 which produced 10.35%(v/v) ethanol(13.1%. v/v) with the viability of 30.44% after 5 days of fermentation. Both of the 20-1 and 11-1 strains were identified as Saccharomyces cerevisiae.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1218-1226
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• 1993

A method, so called 'successive cracking method,' for measuring residual stresses in a circular disk is proposed. In this method residual stresses are evaluated using a fracture mechanics approach, that is, the strains measured at a point on a edge of the disk as a crack is introduced and extended from the edge are used to deduce the residual stress distribution which existed in the uncracked disk. Through finite element analysis and comparative experiments with generally used sectioning method, the successive cracking method is shown to be valid, simple and effective to measure 2-dimensional residual stress distribution in a circular disk.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.297-300
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• 2004

The various microbial tests were performed to determine bioremediation agent capacity for eight strains isolated from the oil contaminated regions. Two tests for isolated strains were conducted such as cell hydrophobicity and emulsifying activity. The biodegradation of SHM (saturated hydrocarbon mixture) and AHM (aromatic hydrocarbon mixture) with the strains also was carried out. The strains having higher cell hydrophobicity and emulsifying activity degraded petroleum oil effectively. The degradation capacity for SHM was represented more than 90% in YS-7 and WLH-1 of isolated strains, and KH3-2 were capable of degrading AHM. Especially, WLH-1 as yeast was shown more than two or three times in the degradation capacity of automobile engine lubricants and the biomonitoring results of contaminated soil for residual oil degrading test showed that the hydrocarbon biodegradation was increased in the second treatment by this strain.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.60-64
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• 2008

According to previous research, welding-induced stress in steel structures can significantly affect the fatigue behaviour; it produces initial damage of weldiug part of structure locally and residual stresses reduce the fatigue strength after welding precess. In this study, through continuum damage mechanics, we can estimate the weldiug damage using the stress and strain history during welding process and the effect of welding residual stress for assessment of fatigue life. The variation of welding-induced stresses and strains need be traced precisely in advance for a reliable weldiug damage assessment. In this study, a damage and fatigue analysis techniques for steel structures with welding-induced residual stress are presented. First, We calculate the history of temperature according with welding process. And residual stress with a welding thermal history was evaluated by non-linear thermal stress analysis. Secondly, welding damage and fatigue life are estimated with kinetic damage law.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.3
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• pp.76-82
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• 2000

It is well known that during the oxygen cutting process residual thermal stresses are produced in weldment. The local non-uniform heating and subsequent cooling which takes place during any welding process causes complex thermal strains and stresses to finally lead to residual stresses exceed to the yield stress. High tensile stresses combined with applied structural load in the region near the welded joint can given rise to distortion brittle fracture change of the fatigue strength and stress corrosion cracking. The appropriate treatment of the welded component which reduces the peak of he welding residual stresses is believed to lower risk of the fracture during the service of the structure. In this study the impact loading in oxygen cutting frame was applied to reduce the residual stress. After applying the impact loading redistribution of resid-ual stress was measured by cutting method and the effect of fatigue was tested.