• Journal of Korean Society for Quality Management
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• v.49 no.2
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• pp.183-200
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• 2021

Purpose: This study is to investigate the effects of job instability and job stress on the turnover intention of sports facility workers in the COVID-19 situation, considering the moderating effects of perceived organizational support. Methods: This study surveyed service workers working at public sports facilities in Seoul, Gyeonggi Province and North Chungcheong Province, South Korea. The multi-regression and hierarchical regression analysis were employed to analyze the collected data. Results: The results indicate that all of the factors constituting job instability (organizational, job, and personal factors) had a significant influence on the factors constituting job stress (job characteristic, roll-related, and human relationship factors), except for only the relationship between organizational factor and rol-related factor. Job characteristic and roll-related factors constituting job stress significantly affected turnover intention of sports facility workers. Also, it was found that the perceived organizational support moderated the relationship between job characteristic factors of job stress and turnover intention. Conclusion: Although the COVID-19 created an environment with very high job instability, the negative impacts of job instability and job stress can be minimized through consideration and support for service workers of the organization, reducing turnover intention.

• Transactions of Materials Processing
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• v.15 no.4 s.85
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• pp.311-318
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• 2006

One of the most important quality problems in flat plate leveled from hot rolled coils in cut-to-Iength lines is bowing and cambering when they are cut in small width parts. It is verified analytically and experimentally that residual stress remained in plate is th ε source of the problem. In order to produce low residual stress flat plate from hot rolled coils, the proper conditions of leveling are studied and two things are implemented. One is proper plastic deformation area ratio to reduce residual stress within customer requirement by applying suitable plastic deformation and maintain leveling load within structural strength limit of leveler. The other is maintaining uniform plastic deformation along the width of the plate during leveling. Customer requirement for residual stress is met by applying above 70% of plastic deformation area ratio and uniform deformation along width of coil by adjusting back up rolls according to deformation analysis of work roll and back up roll assembly and leveling tests.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.615-623
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• 2000

The industrial application of hydroforming has a great potential in saying cost and achieving dimensional accuracy in automotive industry presently. The aim of the following article is to investigate the effect of process parameters on hydroformed part. Firstly, we have to investigate the change of mechanical properties for sheet and pipe material according to various radius/thickness ratio(r/t). The change of mechanical properties affects the yield stress more than the total elongation. Increase of yield stress for pipe has a bad influence on formability of hydroforming. Among the roll-forming process, the sizing process didn't change mechanical properties. The process parameters such as the initial pressure, mandrel shape and friction have seriously influenced on formability of hydroforming. Therefore we need to check formability of given material through the FE analysis in the beginning stage of process design and the predicted hydroforming process parameters ate generally a good starting point for the prototype tryout stage. The results of pretending, hydroforming analysis using FE model are good agreement with experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1451-1456
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• 2003

In code roll forming processes, the sheet metal strip is gradually and successively bent into a desired profile. Occurrence of buckling is one of the major defects. Buckling may occur due to longitudinal stress and it is difficult to predict buckling behavior. In this study an analytical method for buckling behavior during roll forming is proposed. All numerical simulations are performed by finite element analysis. The behavior of buckling can be predicted with the simulation modeling of the finite element method.

• Explosives and Blasting
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• v.17 no.4
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• pp.32-50
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• 1999

This study deals with interface charactristics of tube and tubesheet of the nuclear steam generator by the explosive expansion in order to take advantage of optimum expansion ratio, pull-out strength and leakage tightness and improvement of the resisitance on the stress corrosion cracking for low residual stress. The paper also show the relationship between roll, hydraulic and explosive expansion. The results obtain are as follows (1) Because of the explosive bonding is to use the high speed pressure and energy by the explosive, workability is good, bonding region is homogenous (2) Expansion ratio is 2.7%, Pull-out strength 850kg, Leakage strength $500kg/cm^2$. Clearance gap is 10~30mm in case of explosive expansion and interface structure of the tube and tubesheet is optimum condition. (3) As the transition region of the explosive expansion is inactive, the resistance of the stress corrosion cracking is increases 30~40% compare to the roll and hydraulic expansion.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.3
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• pp.306-312
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• 2017

Press rolls are constantly exposed to physical and heat stresses on their surface and are prone to crack, bruise, and spall if the accumulated stress goes beyond the critical point. Such surface phenomenon can cause them to lose their functionality and eventually lead to a halted production line. Eddy current testing can be considered a useful method to investigate the surface of the roll. The method involves the application of a high intensity magnetic field onto the surface of the roll, and thereby finding any early stage of possible defects. When the method was applied for roll inspection, the cross section of the sensor was regulated as per the overall testing speed. A smaller cross sectional area implied a better resolution but a longer testing time. In this paper, a convenient method to increase both overall system resolution and inspection speed of eddy current roll inspection is suggested by using a devised array sensor structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.279-289
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• 2000

Residual stress induced in U-bending and tube-to-tubesheet joint processes of PWR's row-1 heat exchanger tube was measured by X-ray method and Hole-Drilling Method(HDM). Compressive residual stresses(-) at the extrados surface were induced in U-bending, and its maximum value reached -319 MPa in axial direction at the position of $\psi$ = $0^{\circ}$. Tensile residual stresses(+) of $\sigma_{zz}$ = 45 MPa and $\sigma_{\theta\theta}$ = 25 MPa were introduced in the intrados surface at the position of $\psi$ = $0^{\circ}$. Maximum tensile residual stress of 170 MPa was measured at the flank side at the position of $\psi$ = $90^{\circ}$, i.e., at apex region. It was observed that higher stress gradient was generated at the irregular transition regions (ITR). The trend of residual stress induced by U bending process of the tubes was found to be related with the change of ovality. The residual stress induced by the explosive joint method was found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the transition region (TR), and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction.

• Journal of Welding and Joining
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• v.18 no.4
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• pp.38-47
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• 2000

Characteristics of the interface between tube and tube sheet which were formed by explosive expansion and roll expansion, have been studied in the research. The results are as follows: Optimum amounts of explosives for the expansion of Alloy 600 (19.05mm and 15.88mm) were found to be RDX 3.5-8.5g/m. Because explosive expansion caused les strain hardening and increased bounding strength, characteristics of the explosively expanded were better than those of mechanically expanded. As the transition region of the explosive expansion is inactive, the resistance to the stress corrosion cracking increases by 30∼40% compared to the roll and hydraulic expansion.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2006.06b
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• pp.197-204
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• 2006

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1443-1453
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• 2010

We simulated the roughing train of the rod mill of SEAH BESTEEL Inc. using finite element method to inhibit surface cracks initiation on workpiece. We designed 2nd pass (square roll) and applied to this roll in the roughing train of the rod mill. Also, we proposed new pass schedule, which changed roll gap of 3rd and 4th groove by using finite element method. We used shear damage model, which is dependent on shear stress ratio and compared the number of damaged elements on workpiece. A damaged element means surface crack. Consequently, after 2nd pass (square roll) is changed, the error rate decreased by 1.43% when compare to that of the old groove. And the number of damaged elements in the new pass schedule decreased by 37.6%, which is less than present pass schedule.