Finite-element simulation of quenching incorporating improved transformation kinetics in a plain medium-carbon steel

Jung, M.,Kang, M.,Lee, Y.K. Elsevier Science 2012 Acta materialia Vol.60 No.2

An experimental and numerical investigation was conducted to acquire more precise continuous cooling transformation kinetics for the quenching simulation of a plain medium-carbon steel by improving the conversion model of transformation strains to phase fractions. Previous conversion models have limited applications in plain medium-carbon steels with variable bainite start temperatures (B<SUB>s</SUB>) and martensite start temperatures (M<SUB>s</SUB>), which are cooling rate dependent and cannot be distinguished on dilatometric curves. Therefore, we propose new methods for determining variable B<SUB>s</SUB> and M<SUB>s</SUB>. More accurate diffusive transformation kinetics models were developed based on transformation kinetics data converted from continuous cooling dilatometric curves and considering variable B<SUB>s</SUB>. The martensitic transformation kinetics model was also improved using the quantitative relationship between the variable M<SUB>s</SUB> and the enriched carbon content in residual austenite during diffusive transformations. Finite-element simulation of quenching incorporating the improved transformation kinetics was performed to predict the temperature, microstructure, residual stress and distortion of a plain medium-carbon steel cylinder. The pearlite, bainite, and martensite fractions, axial and hoop stresses near the surface, and the degree of distortion calculated using the improved transformation kinetics exhibited markedly better agreement with the measured results than those calculated using the previous transformation kinetics with B<SUB>s</SUB> and M<SUB>s</SUB> held constant. Furthermore, a comparison of the two simulation results provided a detailed understanding of the effects of transformation kinetics on residual stress and distortion.

In situ observation of mesophase transformation behaviour and mechanistic analysis in β-resin

Liu Ben,Yan Xi,Tao Zechao,Li Xiangfen,Lei Shiwen,Zhang Dongqing,Yang Zonghe,Liu Zhanjun 한국탄소학회 2024 Carbon Letters Vol.34 No.1

β-Resin was extracted by solvent separation of refined coal tar pitch. Several analytical methods revealed that β-resin had a better aromatic plane packing structure and a higher number of carbon residues, making it ideal for mesophase transformation. The mesophase transformation process of β-resin (the formation of liquid-crystalline spheres, the growth of mesophase spheres, and the coalescence and disintegration of mesophase spheres) was observed in situ using a polarizing microscope with a hot stage. Moreover, the mesophase transformation mechanism of β-resin was investigated at each transformation stage. The mesophase content and mesophase transformation kinetics were analyzed based on the area method and quinoline insoluble (QI) substitution method. Both methods revealed changes in the mesophase content of β-resin. However, the test results of the two methods were slightly different at the initial stage of mesophase transformation and tended to be consistent during the later stage.

Kinetic Model to Investigate the Effect of Cooling Rate on δ-Ferrite Behavior and Its Application in Continuous Casting of AISI 304 Stainless Steel

Tahereh Zargar,Fazlollah Sadeghi,Jong Wan Kim,Jae Sang Lee,Yoon‑Uk Heo,Chang Hee Yim 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.9

The prediction of M-shaped δ-ferrite content along the thickness direction of continuously cast 304 austenitic stainless steelslab was performed using a diffusion-controlled phase transformation module of Thermo-Calc software. The surface andcenter of the slab, which solidified with different cooling rates and secondary dendrite arm spacing, were used for kineticcalculations. Comparison between observations and calculations for slab specimens demonstrated that the moving-boundarymodel could predict retained δ-ferrite content according to various thermal histories. After this validation, the effects ofdifferent cooling rates at liquid and solid-state were analyzed to understand the importance of each stage on the diffusioncontrolledδ → phase transformation. Decrease in solid-state cooling rate generally had a larger effect on the reduction ofδ-ferrite during cooling when the solidification rate was fast (27.75 °C/s) than when it was slow (0.075 °C/s). This model canbe used to predict and control δ-ferrite behavior under different thermal histories during slab casting and welding practices.

SOLUTION OF A GENERAL FAMILY OF FRACTIONAL KINETIC EQUATIONS ASSOCIATED WITH THE GENERALIZED MITTAG-LEFFLER FUNCTION

Dinesh Kumar,최준상,H. M. Srivastava 경남대학교 수학교육과 2018 Nonlinear Functional Analysis and Applications Vol.23 No.3

Fractional kinetic equations are investigated in order to describe the various phenomena governed by anomalous reaction in dynamical systems with chaotic motion. Many authors have provided solutions of various families of fractional kinetic equations involving such special functions as (for example) a generalized Bessel function of the first kind [18] and the Aleph function [6]. Here, in this paper, we aim at presenting solution of a certain general family of fractional kinetic equations associated with the generalized Mittag- Leffler function. It is also shown that the result presented here includes, as its special cases, solutions of many fractional kinetic equations which were investigated in earlier works. In our investigation, we have found it to be more convenient to use (and the closed-form results derived here appear to be considerably simpler by using) the Sumudu transform instead of the classical Laplace transform.

망간산화물(birnessite)에 의한 수용액 중 Tetracycline의 산화-변환반응에 대한 연구

엄원숙(Won Suk Eom),김소희(So Hui Kim),신현상(Hyun Sang Shin) 大韓環境工學會 2015 대한환경공학회지 Vol.37 No.2

본 연구에서는 잔류의약물질로써 환경에서 노출 빈도가 높은 항생물질인 Tetracycline (TTC)을 대상으로 수용액 상에서의 망간산화물(birnessite)을 이용한 산화-변환 반응을 통한 제거와 용존성 자연유기물인 휴믹산(HA) 존재에 따른 영향을 조사하였다. TTC의 산화-변환 제거 특성 실험은 다양한 반응조건(반응시간, 망간산화물 주입량 및 pH 등)에서 회분식으로 조사하였으며, HA의 영향은 pH (3~9)와 HA농도 변화에 따라 조사하였다. 실험결과는 유사-일차 반응속도식을 적용하여 해 석하였으며, 본 실험조건(TTC=0.25 mM, δ-MnO₂=1.0 g/L)에서의 TTC의 산화-변환 제거 반응속도상수(k, hr-1)는 pH가 감소함 에 따라 0.98 (pH 9)에서 2.97 (pH 3)로 일정하게 증가하였고, 망간산화물 주입량(1~2 g/L)이 2배 증가할 때 반응속도 상수는 약 1.3배 정도 증가하였다. HA (5 mg-C/L) 존재 시 망간산화물에 의한 TTC 변환제거는 pH≥6에서 반응효율 상승을 나타냈 으며, HA의 주입농도(1~10 mg-C/L, at pH 6)의 증가에 따라 일정하게 증가함을 확인하였다. 이상에서 얻은 연구결과는 기존 문헌에 제시된 TTC 반응기작과 비교 해석하였고, 망간산화물을 매개로 한 TTC의 산환-변환 제거 반응특성과 HA의 존재가 미치는 영향에 대하여 고찰하였다. An investigation on the removals of tetracycline (TTC), which is a family of antibiotics widely founded in the environment, from the aqueous solution by birnessite(δ-MnO₂)-mediated oxidative transformation was described. This study also examined the potential effect of the naturally occurring substances, humic acid (HA) on the oxidative transformation. The experiment was carried out in various conditions (reaction time, Mn oxide loadings, pH) and in the presence of HA as a batch test. The removals of TTC followed pseudo-first order reactions, and rate constants (k, hr-1) for the removals of TTC were constantly increased with decreasing pH from 0.98 (pH 9) to 2.97 (pH 3). The rate constants also increased about 1.3 times when the birnessite loading increased from 1 to 2 g/L. Presence of HA (5 mg-C/L, at pH≥6) caused some enhancement in the removals of TTC as compared to the control, and also showed the removal efficiencies of TTC in the birnessite mediated systems (TTC=0.25 mM, δ-MnO₂=2.0 g/L, pH 6) increased with increasing HA concentrations (1~10 mg-C/L). The results obtained from the oxidative transformation of TTC and the effect of HA were discussed in terms of reaction characteristics and mechanism.

A TYPE OF FRACTIONAL KINETIC EQUATIONS ASSOCIATED WITH THE (p,q)-EXTENDED τ-HYPERGEOMETRIC AND CONFLUENT HYPERGEOMETRIC FUNCTIONS

Owais Khan,Nabiullah Khan,Junesang Choi,Kottakkaran Sooppy Nisar 경남대학교 수학교육과 2021 Nonlinear Functional Analysis and Applications Vol.26 No.2

During the last several decades, a great variety of fractional kinetic equations involving diverse special functions have been broadly and usefully employed in describing and solving several important problems of physics and astrophysics. In this paper, we aim to find solutions of a type of fractional kinetic equations associated with the $(p,q)$-extended $\tau$-hypergeometric function and the $(p,q)$-extended $\tau$-confluent hypergeometric function, by mainly using the Laplace transform. It is noted that the main employed techniques for this chosen type of fractional kinetic equations areLaplace transform, Sumudu transform, Laplace and Sumudu transforms, Laplace and Fourier transforms, $P_\chi$-transform, and an alternative method.

Aqueous phase degradation of methyl paraben using UV-activated persulfate method

Dhaka, Sarita,Kumar, Rahul,Khan, Moonis Ali,Paeng, Ki-Jung,Kurade, Mayur B.,Kim, Sun-Joon,Jeon, Byong-Hun Elsevier 2017 Chemical Engineering Journal Vol.321 No.-

<P><B>Abstract</B></P> <P>Methyl paraben (MP), a widely used preservative, exhibits endocrine-disrupting properties with estrogenic activities. The aqueous phase degradation of MP, using UV-activated persulfate method, was investigated in the present study. The combination of UV irradiation and persulfate anion successfully degraded MP showing 98.9% removal within 90min. A quenching experiment using ethanol (EtOH) and <I>tert</I>-butyl alcohol (TBA) showed the presence of both radicals (OH<SUP> </SUP> and SO<SUB>4</SUB> <SUP> –</SUP>) in the system; near neutral pH SO<SUB>4</SUB> <SUP> –</SUP> radical was the major species. The influence of various factors such as persulfate dose, initial MP concentration, solution pH, and water matrix components on the degradation kinetics was examined in view of the practical applications of the developed process. The degradation rate of MP was considerably increased as the amount of persulfate increased. The degradation of MP in the UV/persulfate system was pH dependent and more promising near neutral pH (6.5) conditions. The presence of anions such as Cl<SUP>−</SUP>, HPO<SUB>4</SUB> <SUP>2−</SUP> and HCO<SUB>3</SUB> <SUP>−</SUP> showed inhibitory effect towards MP degradation. The presence of humic acid also suppressed the degradation efficiency of MP. The reaction rate followed pseudo-first-order kinetics for all of the degradations. The degradation of MP by UV/persulfate treatment led to the production of seven transformation byproducts, which were identified using ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS). A degradation pathway for MP degradation was also proposed. The results of the present study reveal that the UV/persulfate process could be an effective approach to remove MP from aqueous solutions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Aqueous phase MP degradation using UV/persulfate method was investigated. </LI> <LI> Degradation rate of MP followed pseudo-first-order kinetics. </LI> <LI> MP degradation was pH dependent. </LI> <LI> HCO<SUB>3</SUB> <SUP>−</SUP>, HPO<SUB>4</SUB> <SUP>2−</SUP> and humic acid exhibited inhibitory effect on MP degradation. </LI> <LI> Hydroxylation and hydrolysis were possible pathways of degradation of MP. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

디지털텍스트의 시각적 변형에 관한 연구 동향 및 실태 분석

진성희(Sung-Hee Jin) 한국콘텐츠학회 2010 한국콘텐츠학회논문지 Vol.10 No.1

연구의 목적은 디지털텍스트의 시각적 변형에 관한 연구 동향을 탐색하고 현재 학습 자료로 사용되고 있는 디지털텍스트의 시각적 변형 실태를 분석하는 것이다. 종합적 메타분석법에 따라 시각적 변형에 관한 선행연구들을 종합적으로 고찰하여 분석함으로써 디지털텍스트의 시각적 변형에 관한 연구 동향을 정리하였다. 총 167편의 선행문헌을 분석한 결과 기능주의적 시각적 변형, 역동적 시각적 변형, 상호작용적 시각적 변형 관련 연구로 구분할 수 있었고 각 연구주제별 문헌유형과 연구방법이 분석되었다. 그리고 사례분석법에 의해 디지털텍스트의 시각적 변형 실태가 분석되었다. 우수한 학습 자료로 판단할 수 있는 콘텐츠 12개를 선정하여 연구 동향 결과를 근거로 하여 마련한 분석틀에 따라 각 항목별로 조사하였다. 그 결과 드러난 문제점으로는 첫째, 타이포그래피 관련 기본적인 설계 원칙들이 충실히 반영되지 않은 경우들이 있었다. 둘째, 텍스트의 이해를 증진시킬 수 있는 시각적 설계에 대한 깊은 고려 없이 학습단계별로 내용을 전달하는데 초점을 두고 있었다. 셋째, 웹 테크놀로지가 충분히 활용되지 못하고 있었다. The purpose of this study is to investigate the research trends and the present conditions of real digital texts on Visual Transformation. For the purpose of this study adopted two different methods: meta analysis and case study. The research trends on visual transformation of digital text were investigated through analyzing the total of 167 literature by means of synthetic meta analysis. Relevant literature was categorized into three types of research: functional, dynamic, and interactional transformation. The type of literature and research methods in each literature were analyzed. The present conditions of real digital texts on visual transformation were investigated by means of case study. The well designed 12 e-learning contents selected and analyzed in terms of the analysis framework which was drawn by the research trends. The results suggested problems as follows in designing e-learning contents. Firstly, there were some cases that did not follow the basic design principles related to typography. Secondly, the content was just provided in each learning steps without consideration of design to enhance text comprehension in many cases. Thirdly, web technology adequately was not applied to design e-learning contents.

Improved Method to Verify the Additivity Rule for Pearlite Transformation in Eutectoid Steel

Jeong Min Kim,Sokyun Hong,Kyung Jong Lee 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.2

The additivity rule is beneficial when kinetics between the isothermal and non-isothermal (usually continuous cooling) phasetransformation is interrelated. When isothermal transformation (Time Temperature Transformation (TTT)) follows the Johnson–Mehl–Avrami equation (X = 1 − exp(−kTTTnTTTTTT)), even though the reaction exponent is a function of temperature, ifnTTT is larger than 1.0 , as happens in pearlite transformation, it is confirmed that isothermal kinetics is derived from continuouscooling kinetics by the same approach proposed by Ozawa, if the additivity rule is applicable. In this case, the ContinuousCooling Transformation (CCT) with cooling rate q, is described by X = 1 − exp {−[J∕q]nTTT } , where J = ∫ TeqT k1∕nTTTTTT dT . It issuggested that the additivity rule is applicable when the difference between J(T) from TTT (i.e. JTTT (T) ) and J(T) from CCT(i.e. JTTT←CCT(T) ) is within experimental error. Both TTT and CCT are measured for austenite decomposition to pearlite ineutectoid steel. Considering the error of both CCT and TTT experiments, pearlite transformation is proved to be partiallyadditive. When temperatures are from 610 to 640 °C, pearlite transformation is additive. However, when the temperature is650 °C or above, pearlite transformation is non-additive due to a change of the transformation mechanism, which is confirmedby the isokinetic condition using the Master Curve Method.

Transformation kinetics and density models of quenching and partitioning (Q&P) steels

Kim, Seoknyeon,Lee, Jinwoo,Barlat, Fré,dé,ric,Lee, Myoung-Gyu Elsevier 2016 Acta materialia Vol.109 No.-

<P>Thermal dilatation during an isothermal partitioning process below the martensite start temperature (Ms) was characterized and modeled for quenching and partitioning (Q&P) steel sheet. The dilatations were attributed to changes in the phase composition and phase density due to austenitic decomposition and carbon partitioning. To develop a prediction model for the dilatation during the Q&P process, conventional kinetics models for non-diffusional and diffusional phase transformations were improved by introducing the evolution of the transformation rate parameters during the austenitic decomposition. Furthermore, a kinetics equation for carbon partitioning was also proposed after considering the effect of constituent martensite on the partitioning rate. Finally, variations of the phase densities in the partitioned phases were modeled to describe the effect of carbon partitioning on the dilatation. The proposed models were implemented in a finite element code, and simulated dilatometry tests could accurately capture the experimentally measured dilation behaviors under the Q&P process with single and 2-stage partitioning conditions. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>