• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.583-589
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• 1996

In this study a new analytical model which can describe the relationship between the bridging stress and microstructure has beenproposed in order to investigate the microstructural effect on the R-curve behavior in polycrystalline aluminas since the R-curve can be derived via the bridging stress function. In the currently developed model function the distribution of grain size is considered as a microstructural factor in modeling of bridging stress function and thus the bridging stress function including three constants PM, n, and Cx, can be established analytically and quantitatively. The results indicate that the n value is closely related to the grain size distribution thereby providing a reliability of the current model for the bridging stress analysis. Thus this model which explains the correlation of the bridging stress distribution and microstructual parame-ters is useful for the systematic interpretation of microfracture mechanism including the R-curve behavior in polycrystalline aluminas.

• Archives of Metallurgy and Materials
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• v.64 no.3
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• pp.1175-1182
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• 2019

In this study, we present a new method for obtaining the parameters of the Johnson-Mehl-Avrami-Kolmogorov equation for dynamic recrystallization grain size. The method consists of finite-element analysis and optimization techniques. An optimization tool iteratively minimizes the error between experimental values and corresponding finite-element solutions. Isothermal backward extrusion of the AA6060 aluminum alloy was used to acquire the main parameters of the equation for predicting DRX grain size. We compared grain sizes predicted using optimized and reference parameters with experimental values from the literature and found better agreement when the optimized parameters were applied.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.2960-2967
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• 2021

In this work, a new hardening model is proposed for the depth-dependent hardness of ion-irradiated polycrystals with obvious grain size effect. Dominant hardening mechanisms are addressed in the model, including the contribution of dislocations, irradiation-induced defects and grain boundaries. Two versions of the hardening model are compared, including the linear and square superposition models. A succinct parameter calibration method is modified to parametrize the models based on experimentally obtained hardness vs. indentation depth curves. It is noticed that both models can well characterize the experimental data of unirradiated polycrystals; whereas, the square superposition model performs better for ion-irradiated materials, therefore, the square superposition model is recommended. In addition, the new model separates the grain size effect from the dislocation hardening contribution, which makes the physical meaning of fitted parameters more rational when compared with existing hardness analysis models.

• Journal of The Geomorphological Association of Korea
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• v.26 no.1
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• pp.15-26
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• 2019

In this study, we investigated the grain size, lithological type, and shape of coarse bed materials in the upper and middle reaches of Gongneungcheon River. For this purpose, 11 sampling points were selected along the river. For 100 samples of the coarse bed materials at each point, three axes (long, intermediate, and short) of samples were measured, and their lithological types were also identified. By measuring grain size, the sphericity and flatness of samples were calculated. Finally, every particle was classified into four shape categories: sphere, disc, blade and rod. We found that the grain size in incised meandering reach is the largest. This is mainly due to the supply of coarse materials from steep valley sides along the meandering channel. According to the lithological analysis, all samples were identified as granite, gneiss and schist, and quartz. The proportion of granite decreased, whereas the proportion of gneiss and schist increased downstream. These patterns indicate that the bedrock distribution within the study area accounts for the downstream lithological variation of coarse bed materials. With regard to the grain shape, sphericity gradually decreased while flatness gradually increased downstream. In the case of the shape classification, unlike the general downstream pattern of grain shape, the proportion of the sphere type decreased and the proportion of the blade type increased downstream. Such a reversal change in the downstream direction turns out to be determined by the lithology (such as foliation, bedding and the pattern of weathering) of coarse bed materials.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.76-84
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• 1985

Mechanical property enhancing mechanisms of $Al_2O_3-ZrO_2$ two phase ceramic composites were studied for several compositions of different $ZrO_2$/$Al_2O_3$ ratio. Microstructural analysis of $Al_2O_3-ZrO_3$(pure) composites indicated that pre-existing microcrack due to larger $ZrO_2$ particle at grain boundary extended along alumina grain boundaries within process zone. Microcracks also nucleated when very small $ZrO_2$ particles at the grain boundaries transformed to monoclinic phase at near of main crack tip. These types of microcracks could contribute to the toughening achieved by creating additional crack surface area during crack propagation. Microstructural analyses also showed that the average grain size and abnormal grain size of $Al_2O_3$ were decreased with increasing $ZrO_2$ vol% in $Al_2O_3$ matrix. As a result it could be concluded as follows In TEX>$Al_2O_3-ZrO_3$(pure) system 1. Microcrack nucleation (stress-induced microcracking) and extension was effective mechanism for absorpiton of fracture energy 2, More narrow distribution and smaller grain size of $Al_2O_3$ due to $ZrO_2$particles mainly contributed to main-tatin the strength and hardness.

• Journal of Welding and Joining
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• v.30 no.1
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• pp.64-71
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• 2012

The characteristics of high heat input (342kJ/cm) EG (Electro Gas Arc) welded joint of EH36-TM steel has been investigated. The weld metal microstructure consisted of fine acicular ferrite (AF), a little volume of polygonal ferrite (PF) and grain boundary ferrite (GBF). Charpy impact test results of the weld metal and heat affected zone (HAZ) met the requirement of classification rule (Min. 34J at $-20^{\circ}C$). In order to evaluate the relationship between the impact toughness property and the grain size of HAZ, the austenite grain size of HAZ was measured. The prior austenite grain size in Fusion line (F.L+0.1 mm) was about $350{\mu}m$. The grain size in F.L+1.5 mm was measured to be less than $30{\mu}m$ and this region was identified as being included in FGHAZ(Fine Grain HAZ). It is seen that as the austenite grain size decreases, the size of GBF, FSP (Ferrite Side Plate) become smaller and the impact toughness of HAZ increases. Therefore, the CGHAZ was considered to be area up to 1.3mm away from the fusion line. Results of TEM replica analysis for a welded joint implied that very small size ($0.8\sim1.2{\mu}m$) oxygen inclusions played a role of forming fine acicular ferrite in the weld metal. A large amount of (Ti, Mn, Al)xOy oxygen inclusions dispersed, and oxides density was measured to be 4,600-5,300 (ea/mm2). During the welding thermal cycle, the area near a fusion line was reheated to temperature exceeding $1400^{\circ}C$. However, the nitrides and carbides were not completely dissolved near the fusion line because of rapid heating and cooling rate. Instead, they might grow during the cooling process. TiC precipitates of about 50 ~ 100nm size dispersed near the fusion line.

• Journal of The Geomorphological Association of Korea
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• v.17 no.3
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• pp.77-88
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• 2010

The grain size characteristics of the Asian Dust(AD) in Seoul during the spring 2010 are analyzed by the different pretreatment procedures. The mean values of the AD samples by the minimal dispersion are 19~56㎛ and the NAD(Non-Asian Dust) samples are 37~92㎛. Contrastively, the mean values of AD and NAD samples by the ultimate dispersion are 13~20㎛ and 14~30㎛, respectively. It is revealed that the particles less than approximately 20㎛ and 40㎛ by the minimal and ultimate dispersion, respectively, are introduced into the atmosphere in the Korean Peninsular by the AD events with the peaks of approximately 0.5㎛, 1.5㎛ and 8.5㎛ by the minimal dispersion, and 0.5㎛ and 7.5㎛ by the ultimate dispersion. Also, the charateristics of AD samples showing similar grain size characteristics to the loess samples rather than the NAD samples indicates long distance origin from China so on. The differences of grain size characteristics between the AD and loess samples may result in duration and intensity of weathering processes.

• Journal of The Geomorphological Association of Korea
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• v.27 no.3
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• pp.13-24
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• 2020

This study analyzed the characteristics of the grain size distribution of the sediments obtained from the flooding in Ibang-myeon, Changnyeong-gun, which was caused by the collapse of a embarkment on the Nakdong River on August 9, 2020. As a results, it was found that the mean grain size decreases and the sorting becomes poorer as the distance from the embarkment collapse point increases. This is attributed to the fact that the transport energy of the river decreases when flooding occurs, ensuring that coarse-grained sediments are deposited first. Further, as the transport energy further reduces and becomes dispersed, the sorting for the fine-grained sediments becomes poor. Considering the characteristics of spatial distribution, sediments along the farm road showed the properties of floodplain deposits that transport to natural levee and back swamp due to river flooding. On the other hand, sediments along the irrigation ditch exhibited the properties of the deposits that are carried by the flow backward of ditch from the river after the collapse of the embarkment. The results of this study are significant because characteristics of flood sediments were elucidated for major rivers where flooding rarely occurs due to the recently built artificial structures. In addition, by applying the grain size distribution characteristics of present river flood sediments, it will be able to contribute to clarifying the sedimentary environments of the paleo river flood deposits.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.20 no.1
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• pp.13-24
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• 2017

This study is to provide basic data on ecology and morpho-pedo milieu by analyzing diatom and grain size of Mt. Jeombong forest wetland. Sample was collected from 6 points and named sample 943, 932, 885, 881A, 881b, 849. Sample 934 could not identify diatom, and the soil layer was colluvium deposited by mass-movement process. Layer of sample 932 was developed in the lower velocity environment, and presence frequence of complete diatom was very low. Hydrological situation of sample 855 was analysed in oligosaprobien environments. Sample 881A was meso-saprobic environments, velocity was slow area that inhabit musci bryopsida and sphaerocarpus. Sample 881B was acidic wetland in oligosaprobien environments. Sample 849 was analysed in oligosaprobien environments. The results of soil and diatom analysis are well reflect on wet environments of mountain wetlands and also it will expected to be in the help of environmental changes study of mountain wetlands.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.4
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• pp.43-52
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• 2005

It is known in some literatures that the B value is not equal to unity in saturated soil when effective stress is given, in which the B Value is the ratio of measured excess pore water pressure and isometric loading pressure. In this study the B value was measured on various effective stresses and on various incremental loading stresses in various grain size of specimens with saturated sand. The test results showed that the B value was affected largely by grain size of sand in specimen and the amount of effective stress. There was the semi-logarithmic relationship between B value and effective stress, and also there was the linear relationship between the gradient of the former semi-logarithmic relationship and grain size of specimen.