1,720,959 research outputs found
A study on development of a computer-aided-design system for roll pass and roll profile design in bar rolling
No full text학위논문(석사) - 한국과학기술원 : 기계공학과, 1998.2, [ iii, 104 p. ]한국과학기술원 : 기계공학과
The Effect of Processing Parameters on Flatness of the Strip during Coiling Process by Elastic Stress Analysis
Get PDFMicrostructure evolution modeling of square-diamond pass hot bar rolling of AISI 4135 steel
No full textIn this study, kinetics of the static (SRX) and metadynamic recrystallization (MDRX) of AISI4135 steel was investigated using hot torsion tests. Continuous torsion tests were carried out to determine the critical strain for dynamic recrystallization (DRX). The times for 50% recrystallization of SRX and MDRX were determined, respectively, by means of interrupted torsion tests. Furthermore, austenite grain size (AGS) evolution due to recrystallization (RX) was measured by optical microscopy. With the help of the evolution model established, the AGS for hot bar rolling of AISI4135 steel was predicted numerically. The predicted AGS values were compared with the results using the other model available in the literature and experimental results to verify its validity. Then, numerical predictions depending on various process parameters such as interpass time, temperature, and roll speed were made to investigate the effect of these parameters on AGS distributions for square-diamond pass rolling. Such numerical results were found to be beneficial in understanding the effect of processing conditions on the microstructure evolution better and control the rolling processes more accurately.The authors wish to thank for the Grants of International Collaboration between
KAIST and Deakin University and National Research Laboratory Program from Ministry of Science and Technology, without which this research would not be possible
Surface wrinkle defect of carbon steel in the hot bar rolling process
No full textIt is well known that surface defect is a common problem encountered in the multi-stage hot bar rolling process of carbon steel. In this study, the phenomenon was investigated by simulating the process by the finite element technique to identify the location where the surface defect might occur and checking the surface qualities obtained from the compression tests at various temperatures and strain rates to clarify the important parameter governing the possible surface defect formation. Also, the surface temperature was measured by employing pyrometer to support the experimental observation. The levels of temperature and specific deformation energy obtained from finite element simulations depending on the roll groove geometry were compared with the experimental observation to better understand the formation of the surface defect in the hot rolled bar. Based on this study, the surface defect might be formed by dissipating the excessive deformation energy accumulated by generating the new surface at the lower level of temperature where recrystallization cannot occur. According to this work, the comparison of the specific deformation energy level for determining the instability of the hot working process might be interesting for further investigation. (C) 2008 Elsevier B.V. All rights reserved.The authors wish to thank for the grants from the POSCO and
Korea Science and Engineering Foundation (KOSEF) through the
National Research Laboratory Program funded by the Ministry of
Science and Technology (No. R0A-2006-000-10240-0)The techni-
cal support of the POSCO to carry out the hot compression tests was
very much appreciated
Optimization of Flatness of Strip during Coiling Process based on Evolutionary Algorithms
No full textIn this paper, an optimization study was conducted for improving flatness of the strips during coiling process. The evolutionary optimizer coded by MATLAB is used for reducing axial inhomogeneity of the stress distribution and the maximum compressive stress calculated by Love's elastic solution within a thin strip during the coiling process which might cause irregular surface profile of the strip. An improved differential evolution (DE# method employing opposition-based concept is newly proposed in the present work and is used along with several well-established evolutionary algorithms #EAs) to obtain the optimal processing parameters such as spool geometry and coiling tension of the strip coiling process. It was found that the newly proposed differential evolutionary algorithm outperformed other EAs according to the present study. This kind of optimization studies will be helpful in reducing the edge wave defects during the strip coiling process to improve product qualit
오스테나이트 결정립 미세화와 균질화를 위한 유한요소해석을 이용한 선재압연 공정설계
No full text학위논문(박사) - 한국과학기술원 : 기계공학전공, 2003.8, [ xv, 191 p. ]As the need for social infrastructures with large dimension and environment friendly light automobile increases, the importance of manufacturing steel with high strength is ever increasing. Among the various thermomechanical treatments, grain refinement is the only way to increase both the strength and toughness. Thus, it is of great importance to develop a technique to obtain finer grains in industry.
Many studies have been carried out in developing mathematical models describing the relationship between the process parameters and mechanical properties of the rolled products. These models have been applied to industrial strip rolling process and many successful applications have been reported so far. In bar rolling area, not much study has been conducted due to the difficulties in modeling the three-dimensional material flow. To overcome this problem, several researchers in industry have developed approximate deformation models and predicted the average grain size. This approach can predict the microstructural changes for the industrial rolling having more than 30 passes only in a few seconds. Despite its computational advantage, the approach can provide only the average grain size with no information on local microstructures. Thus, more advanced approach which can predict the local microstructure in detail is required.
In this study, an integrated microstructure modeling system was developed for prediction of the local microstructural change during bar rolling by combining the finite element (FE) analysis with a microstructural model. The metallurgical model available in the literature was adopted and integrated with the three-dimensional finite element analysis based on the rigid-thermoviscoplastic formulation. The current study focused on the prediction of austenite grain size (AGS) before the transformation stage during cooling.
While several groups conducted studies on the FE based microstructural modeling, rigorous verification through bar rolling experi...한국과학기술원 : 기계공학전공
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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