• Journal of Korea Foundry Society
• /
• v.40 no.1
• /
• pp.1-6
• /
• 2020

Many studies involving a thermal stress analysis using computational methods have been conducted, though there have been relatively few experimental attempts to investigate thermal stress phenomena. Casting products undergo thermal stress variations during the casting process as the temperature drops from the melting temperature to room temperature, with gradient cooling also occurring from the surface to the core. It is difficult to examine thermal stress states continuously during the casting process. Therefore, only the final states of thermal stress and deformations can be detemined. In this study, specimens sensitive to thermal stress, were made by a casting process. After which the residual stress levels in the specimens were measured by a hole drilling method with Electron Speckle-Interferometry technique. Subsequently, we examined the thermal stresses in terms of deformation during the casting process by means of a numerical analysis. Finally, we compared the experimental and numerical analysis results. It was found that the numerical thermal stress analysis is an effective means of understanding the stress generation mechanism in casting products during the casting process.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.9
• /
• pp.100-106
• /
• 2020

This study analyzes the residual stress of AISI 1536V for an engine shaft of the shipbuilding industry and AISI A387 for a reactor shell of the chemical refining industry by the hole drilling method with a strain gauge rosette, which transforms fine mechanical changes into electrical signals. Tensile residual stress is generated in the forging and heat treatment process because specimens are affected by thermal stress and metal transformation stress. In the heat treatment process, the residual stress of AISI A387 is almost 170% the yield strength at 402 MPa. Since during the machining process, variable physical loads are applied to the material, compressive residual stress is generated. Under the same condition, the mechanical properties greatly affect the residual stress during the machining process. After the stress-relieving heat treatment process, the residual stress of AISI A387 is reduced below the yield strength at 182 MPa. Therefore, it is necessary to control the temperature, avoid rapid heat change, and select machining conditions depending on the mechanical properties of materials during manufacturing processes. In addition, to sufficiently reduce the residual stress, it is necessary to study the optimum condition of the stress-relieving heat treatment process for each material.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.05a
• /
• pp.201-204
• /
• 2008

In this paper, several process parameter studies of the manufacturing process of the steel cords are carried out to verify the relation between the process parameters and the residual stresses on the steel cords. At first, the finite element analysis of the drawing process is performed and the residual stress distributions with respect to the wire material and the area reduction ratio are obtained. The residual stress of the drawn wire is imported the finite element analysis of the twisting process as an initial stress. After that a parameter study of the twisting process is carried out. The process parameters are the applied tension, the over-twisting angle and the tensile strength of the drawn wire. Based on these studies, the optimum values of the process parameters which can remove or reduce the undesired residual stresses are determined. The optimum value of the process parameters are confirmed by the finite element analysis of the elastic recovery process of the steel cords. Finally, the finite element analysis of the roller straightening process is done to study the variation of the distribution of the residual stress before and after the process.

• Transactions of Materials Processing
• /
• v.12 no.4
• /
• pp.302-307
• /
• 2003

Hot rolled strip is cooled by air and water in Run-Out-Table. In this process, phase transformation and shape deformation occurs due to temperature drop. Because of un-ideal cooling condition of ROT, irregular shape deformation and phase transformation arise in the strip. which affect the strip property and lead to the residual stress of strip. And these exert effects on the following processes, coiling process, coil cooling process, and re-coiling process. Through these processes, the residual stress becomes higher and severe. For the prediction of residual stress distribution and shape deformation of final product, Finite element(FE) based model was used. It consists of non-steady state heat transfer analysis, elasto-plastic analysis. thermodynamic analysis and phase transformation kinetics. Successive FEM simulation were applied from ROT process to coil cooling process. In each process simulation, previous process simulation results were used for the next process simulation. The simulation results were matched well with the experimental results.

• Transactions of Materials Processing
• /
• v.19 no.2
• /
• pp.101-106
• /
• 2010

CB100 is one of the channel type products in the steel beam. In this study, rolling process of CB100 is analyzed by 3D FEM simulation and rolling process. FEM simulation result is compared with rolling process data. Also the intermediate & finishing roll stress analysis is carried out and the suitability of the roll through roll stress resultant analysis is evaluated. In order to decrease the roll stress, new pass schedule is developed for stable load balance between intermediate and finishing rolling stand. Therefore new rolling pass schedule is verified by the analysis results of rolling process and roll stress. By the analysis results, the credibility of rolling process analysis was obtained and it was determined that the possibility of roll damage between intermediate and finishing mill was high. So the new pass schedule was developed. Through the result of rolling process and roll stress analysis, it was obtained that the reduction of roll stress and stable load balance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.05a
• /
• pp.405-408
• /
• 2004

The forming load and the stress applied to dies during cold forming of automotive part using microalloyed forging steel are examined with finite element analysis. The forming load and the stress applied to dies at each process step are investigated for two types of forming process. The changes in forming process significantly affect the variation of firming load and the stress at each process step, thus it is considered that the die lift will be remarkably changed with the type of forming process, therefore optimal process design is necessary to obtain an increased the die life and to make the die life uniform at each process step.

• Nuclear Engineering and Technology
• /
• v.54 no.3
• /
• pp.849-859
• /
• 2022

Feed-water valves (FWVs) are used to regulate the flow rate of water entering steam generators, which are very important devices in nuclear power plants. Due to the working environment of relatively high pressure and temperature, there is strength failure problem of valve body in some cases. Based on the thermo-fluid-solid coupling model, the valve body stress of the feed-water valve in the opening process is investigated. The flow field characteristics inside the valve and temperature change of the valve body with time are studied. The stress analysis of the valve body is carried out considering mechanical stress and thermal stress comprehensively. The results show that the area with relatively high-velocity area moves gradually from the bottom of the cross section to the top of the cross section with the increase of the opening degree. The whole valve body reaches the same temperature of 250 ℃ at the time of 1894 s. The maximum stress of the valve body meets the design requirements by stress assessment. This work can be referred for the design of FWVs and other similar valves.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.21 no.6
• /
• pp.50-59
• /
• 2022

The design of the substrate significantly affects the thermal history and the residual stress formation in the vicinity of a repaired region by a directed energy deposition (DED) process. The occurrence of defects in the repaired region depends on the thermal history and residual stress formation. The objective of this study was to investigate the influence of the inclined angle and depth of the substrate on the thermal and residual stress characteristics in the vicinity of a repaired region by a DED process through two-dimensional finite element analyses (FEAs). The temperature and residual stress distributions in the vicinity of the repaired region were predicted according to the combination of the inclined angle and depth of the substrate. The effects of the inclined angle and depth on the depth of the heat affected zone and the maximum value of the residual stress were examined. A proper combination of the inclined angle and depth of the substrate was estimated to decrease the residual stress in the vicinity of the repaired region.

• Journal of the Semiconductor & Display Technology
• /
• v.16 no.4
• /
• pp.68-74
• /
• 2017

Nanoimprint lithography (NIL) is a next generation technology for fabrication of micrometer and nanometer scale patterns. There have been considerable attentions on NIL due to its potential abilities that enable cost-effective and high-throughput nanofabrication to the display device and semiconductor industry. Up to now there have been a lot of researches on thermal NIL, but most of them have been focused on polymer deformation in the molding process and there are very few studies on the cooling and demolding process. In this paper a cooling process of the polymer resist in thermal NIL is analyzed with finite element method. The modeling of cooling process for mold, polymer resist and substrate is developed. And the cooling process is numerically investigated with the effects of imprinting temperature and residual layer thickness of polymer resist on stress distribution of the polymer resist. The results show that the lower imprinting temperature, the higher the maximum von Mises stress and that the thicker the residual layer, the greater maximum von Mises stress.

• Journal of Korean Academy of Nursing
• /
• v.24 no.1
• /
• pp.18-32
• /
• 1994

It is important to understand that patients with hemiplegia are under stress during the rehabilitation process. This study was designed to determine what changes occur in the stress perceived by these patients during the rehabilitation process. and what changes occur in the ways they coped with stress. A decriptive study with a longitudinal design was conducted. A total of 57 patients with hemiplegia who were admitted to one general hospital made up the sample for this study. A questionnaire, observations and interviews were used for the data collection which was done in three phases(within one week after admission : within one week before discharge ; within one month after discharge ). Data were analyzed using t-test, ANOVA repeated measures of ANOVA, and post hoc paired t -test, Bonferroni correction. The results of this study are : 1. Changes in the perception of stress during the rehabilitation process : There was a statistically significant differencs in the perception of stress among these patients during the rehabilitation process. On the post-hoc test. the perception of stress showed a statistically significant decrease from admission to discharge. The perception of psychological stress was high during the rehabilitation process as compared with the perception of physical and social stress. 2. Changes in the way the patients coped during the rehabilitation process : On admission passive coping was used by most of the subjects(91.2％). Passive coping showed an decrease from admission to discharge, but an increase from discharge to follow-up at one month post discharge. There was, however, no statistically significant changes in the way the patients coped during the rehabilitation process. 3. Changes in perception of stress during the rehabilitation process according to variables. Perception of stress among patients classified as So-Um was higher during the rehabilitation process, when compared with patients classified as So- Yang and Tae-Um. There was, however, no statistically significant difference in perception of stress over time. The patients with right sided paralysis perceived higher stress than those with left sided paralysis. There was, however, no statistically significant difference in perception of stress over time. Hence, stress was not influenced by which side was paralyzed th frequency of the relapse of the disease, or the time in the rehabilitation process. 4. Changes in coping during the rehabilitation process according to variables. There was a statistically significant difference in the way the patients coped at follow- up according to the three different kinds of the constitution groups. In other words, coping was not used by patients classified as Tae-Um but was used by those classified as So-Um. On the repeated measures of ANOVA, there was a statstically significant difference in stress over time, and an interaction between constitution and time. But the way of coping during the rehabilitation process was not influenced by which side was paralyzed nor by the frequency of the relapse of the disease. In conclusion, perception of psychological stress was high during the rehabilitation process, as compared to perception of physical and social stress. There was a statistcally significant difference in the perception of stress over time, Perception of stress showed a gradual decrease from over admission to follow-up period. There was. however, no statistically significant difference in the way of coping over time. Passive coping was used by most of patients. In the study, these findings suggest a need for nursing care related to the psychological support for patients with hemiplegia both in the hospital as well as at home, and the need for education and counseling on independent self-care to help the hemiplegic patients adapt to stress using active coping.