Grain Size Effect on Multi-Stage Micro Deep Drawing of Micro Cup with Domed Bottom

Wen Ting Li,Ming Wang Fu,Ji Lai Wang,Bao Meng 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.6

A two-stage micro deep drawing system was designed and developed to manufacture a micro cup with domed bottom. The copper blank was annealed at three different conditions to obtain different grain sizes in such a way to study the grain size effect on the deformation behavior and thickness variation of the micro part. To investigate the instantaneous effect and deformation behavior, finite element simulation was used to simulate the whole drawing process. It revealed that the fracture in the place with the thinnest thickness in the micro part drawn from a circle blank with residual stress induced in blanking can be easily happen and the deformation load in the first-stage decreases more than that in the second-stage with the increase of grain size. Moreover, the micro part with a larger grain size has more nonuniform thickness and severer thinning around the punch corner. The surface roughness at the bottom of micro part increases with the grain size. The surface roughness at the wall of it, however, decreases with the deformation stage mainly due to the ironing effect. The research promotes the understanding of grain size effect on multi-stage micro deep drawing and facilitates the development of microforming process.

TMCP로 제조된 고강도 베이나이트강의 유효결정립도와 저온인성에 미치는 Cu와 B의 영향

이승용,황병철,Lee, Seung-Yong,Hwang, Byoungchul 한국재료학회 2014 한국재료학회지 Vol.24 No.10

Effects of Cu and B on effective grain size and low-temperature toughness of thermo-mechanically processed high-strength bainitic steels were investigated in this study. The microstructure of the steel specimens was analyzed using optical, scanning, and transmission electron microscopy; their effective grain size was also characterized by electron back-scattered diffraction. To evaluate the strength and low-temperature toughness, tensile and Charpy impact tests were carried out. The specimens were composed of various low-temperature transformation products such as granular bainite (GB), degenerated upper bainite (DUB), lower bainite (LB), and lath marteniste (LM), dependent on the addition of Cu and B. The addition of Cu slightly increased the yield and tensile strength, but substantially deteriorated the low-temperature toughness because of the higher volume fraction of DUB with a large effective grain size. The specimen containing both Cu and B had the highest strength, but showed worse low-temperature toughness of higher ductile-brittle transition temperature (DBTT) and lower absorbed energy because it mostly consisted of LB and LM. In the B-added specimen, on the other hand, it was possible to obtain the best combination of high strength and good low-temperature toughness by decreasing the overall effective grain size via the appropriate formation of different low-temperature transformation products containing GB, DUB, and LB/LM.

Specimen size effects on the weakening of a bulk metastable austenitic alloy

Shin, C.,Lim, S.,Jin, H.h.,Hosemann, P.,Kwon, J. Elsevier Sequoia 2015 Materials science & engineering Structural materia Vol.622 No.-

In this work, we are investigating the scaling effects on an austenitic stainless steel with changing grain size using microcompression testing. It is our aim to evaluate at what sample-to-grain size ratio the mechanical properties such as yield stress deviate from the macroscopically determined data. It was found that decreased yield stresses with decreasing specimen size (weakening) occur during the microcompression. The weakening was observed when the diameter-to-grain size ratio (D/d) dropped below a critical value. The effect of the grain size on the critical value, above which the bulk property can be obtained, was systematically investigated utilizing a wide range of D/d values (0.5-30) for specimens with a grain size ranging from 0.3 to 2μm. It was found that the critical D/d value decreases with increasing grain size. A simple analytical model was developed, which is applicable to both micropillar and tensile tests. Comparison of the model equations with experimental data showed that the reduction in yield stress with sample size can be associated with the weaker near-surface zone, which has a reduced strength compared to the specimen interior zone. Furthermore, this study suggests that the size of the near-surface zone may be related to the dislocation structures in near-surface grains, and therefore the overall behavior is governed by the grain size and stacking fault energy.

Grain size effects on magnetomechanical damping properties of ferromagnetic Fe–5wt.% Al alloy

Seo, Young Ik,Lee, Baek-Hee,Kim, Young Do,Lee, Kyu Hwan Elsevier 2006 Materials science & engineering. properties, micro Vol.431 No.1

<P><B>Abstract</B></P><P>To clarify the effects of grain size on the damping capacity of a ferromagnetic Fe–5wt.% Al alloy with an average grain size of 130–845μm, the magnetomechanical properties and microstructures were studied. The results showed a maximum damping capacity at a certain average grain size. Thus, it was proposed that the damping capacity is proportional to the total area of the 90° domain walls represented by the mean 90° domain width and the saturation magnetostriction. It can be reasonably explained that with grain growth, the saturation magnetostriction increases and the total area decreases. Leading to the result of a maximum damping capacity at a certain average grain size where the best combination of the two factors was found.</P>

Size-dependent compressive strength properties of hard rocks and rock-like cementitious brittle materials

Mohammad Darbor,Faramarzi, Lohrasb,Sharifzadeh, Mostafa 한국자원공학회 2019 Geosystem engineering Vol.22 No.4

Rock engineering projects have always been constructed on different (from micro to macro) scales. This makes understanding rock behaviour at different scales essential. In previous statistical studies on igneous hard rocks, the correlation of uniaxial compressive strength (UCS) values in different diameters with estimations of specimen size effect models was weak. In view of this knowledge gap, the present research proposed a model of appropriate size effect in igneous hard rocks. This research also aimed at discussing the effect of specimen size and grain size on the UCS of concrete specimens. To achieve these aims, studies were conducted in parallel on the previous and new experimental data. Non-linear regression analysis on igneous hard rocks indicated that there is a better agreement between the outputs of the multi-fractal scaling model and the specimen size effect model using the fracture energy theory and the results of previous laboratory tests. In addition, in the experimental study, the grain size effect on the predictions of specimen size effect models was exhibited. The results of this research can be used for designing engineering projects at different scales.

Effects of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels

Shin, S.Y.,Han, S.Y.,Hwang, B.,Lee, C.G.,Lee, S. Elsevier Sequoia 2009 Materials science & engineering. properties, micro Vol.517 No.1

Effects of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels were investigated in this study. Six kinds of steels were fabricated by controlling the amount of Cu and B addition, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron back-scatter diffraction analysis. The tensile test results indicated that the B- or Cu-containing steels had the higher yield and tensile strengths than the B- or Cu-free steels because their volume fractions of acicular ferrite and martensite were quite high. The B- or Cu-free steels had the higher upper shelf energy than the B- or Cu-containing steels because of their lower volume fraction of martensite. In the steel containing 10ppm B without Cu, the best combination of high strengths, high upper shelf energy, and low energy transition temperature could be obtained by the decrease in effective grain size due to the presence of acicular ferrite having fine effective grain size.

논문 : 베이나이트계 고강도강의 샤르피 충격 특성에 미치는 유효결정립도 영향

신상용 ( Sang Yong Shin ),한승엽 ( Seung Youb Han ),황병철 ( Byoung Chul Hwang ),이창길 ( Chang Gil Lee ),이성학 ( Sung Hak Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.10

This study is concerned with the effect of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels. Six kinds of steels were fabricated by varying alloying elements and hot-rolling conditions, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron back-scatter diffraction analysis. The tensile test results indicated that the B- or Cu-containing steels had the higher yield and tensile strengths than the B- or Cu-free steels because their volume fractions of bainitic ferrite and martensite were quite high. The B- or Cu-free steels had the higher upper shelf energy than the B- or Cu-containing steels because of their higher volume fraction of granular bainite. In the steel containing 10 ppm B without Cu, the best combination of high strengths, high upper shelf energy, and low energy transition temperature could be obtained by the decrease in the overall effective grain size due to the presence of bainitic ferrite having smaller effective grain size.

Discrimination of sediment provenance in the Yellow Sea: Secondary grain-size effect and REE proxy

Jung, H.S.,Lim, D.,Jeong, D.H.,Xu, Z.,Li, T. Elsevier Science Ltd ; Pergamon 2016 Journal of Asian earth sciences Vol.123 No.-

<P>This study analyzed grain size and elemental concentrations (Al, Mg, Fe, and rare earth elements (REEs)) in 91 surface sediments to elucidate sediment provenance in the Yellow Sea. Elemental concentrations were normalized by Al concentration (C-element/C-Al) to minimize the sediment grain-size effect (GSE). However, noticeable linear relationships between AI concentration (or mean grain size) and the ratio (e.g., Mg/Al or Fe/Al) appeared unexpectedly in pair diagrams. The spatial distribution patterns of Fe/Al and Mg/Al ratios were also similar to the pattern of mean grain size. This implies that the GSE was not removed completely, even after the normalization process. Thus, great care must be taken when applying the ratios of C-element/C-Al as a proxy of sediment provenance. To improve provenance discrimination of the sediments in the Yellow Sea, the difference between the REE distribution patterns of Chinese and Korean river sediments, expressed as delta (delta = REE*(La) - REE*(Lu)), was calculated, and the spatial distribution patterns of the delta values were mapped. The delta values gradually increased from the western to the eastern part of the Yellow Sea, except for low delta values in the southeastern part of the Yellow Sea. This result indicates that the majority of Chinese and Korean river sediments are accumulating near to their respective coasts, except for a deposit along the southwestern coast of Korea in which a considerable amount of sediment from Chinese rivers has been accumulating. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Simulation of the Grain Size Effect in Gas-Sensitive SnO2 Thin Films Using the Oxygen Vacancy Gradient Distribution Model

Jianqiao Liu,Zhaoxia Zhai,Guohua Jin,Yuan Li,Faheema Fairuj Monica,Xuesong Liu 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.1

The model of gradient-distributed oxygen vacancies is utilized in simulatingthe grain size effects of gas-sensitive SnO2 thin films. The distribution profileof oxygen vacancies has a grain size effect and the profile gradient correlatespositively with the radius of the grains. The simulation results show that thegrain size is a fundamental factor dominating the gas-sensing properties ofthin films. The potential barrier height and resistivity have significant grainsize effects when m is between 0.1 and 0.5 nm−1. The size effects on sensorresponse to stimulant gases can be enhanced by increasing the value of m orthe absolute value of α. Two expressions are used to simulate the grain sizeeffect of the sensor response. The expressions act similarly when α < 0.2. The simplified response provides a neat function to quantitatively explain thesensor performance on gases with low partial pressure. Although the accurate response is complicated, it is applicable to theentire concentration range. A small power-law exponent n is calculated from the accurate response expression when a high gasconcentration is employed, illustrating a “saturation effect” of the response.

API X70 및 X80급 라인파이프강의 준정적 및 동적 비틀림 변형 거동

김용진 ( Young Jin Kim ),김양곤 ( Yang Gon Kim ),신상용 ( Sang Youg Shiu ),이성학 ( Sung Hak Lee ) 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.1

This study aimed at investigating quasi-static and dynamic torsional deformation behavior of three API X70 and X80 linepipe steels. Quasi-static and dynamic torsional tests were conducted on these steels. having different grain sizes and volume fractions of acicular ferrite and polygonal ferrite, using a torsional Kolsky bar. The test data were then compared via microstructures and adiabatic shear band formation. The dynamic torsional test results indicated that the steels rolled in the single phase region had higher maximum shear stress than the steel rolled in the two phase region, because the microstructures of the steel rolled in the single phase region were composed mainly of acicular ferrites. In the X80 steel rolled in the single phase region. the increased dynamic torsional properties could he explained by a decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. The possibility of adiabatic shear hand formation was analyzed from the energy required for void initiation and variation in effective grain size.