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Badanie właściwości mechanicznych i mikrostruktury zaczynu cementowego z kulkami szklanymi z wykorzystaniem modelu faza - pole i funkcji ścieżki liniowej do opisu pękania

Han T. S., Chung S. Y., Kim J. S.

Cement Wapno Beton

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2018

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R. 21/83, nr 3

239--250

PL

Zrozumienie właściwości mechanicznych i ich związku z mikrostrukturą zaczynu cementowego jest kluczowe dla oceny jakości istniejących materiałów cementowych i projektowania nowych materiałów cementowych. W pracy tej zastosowano model pola dyfuzyjnego fazy pękania do symulacji propagacji wielu mikrospękań w materiałach cementowych z losowymi sferycznymi pustkami poddanych naprężeniom bezpośrednim. Właściwości mechaniczne oceniane za pomocą tego modelu porównywano z charakterystyką funkcji ścieżki liniowej, jednej z funkcji prawdopodobieństwa małego rzędu. Stwierdzono, że funkcja ścieżki liniowej może być skuteczna do charakteryzowania ciągłości fazy stałej w odniesieniu do właściwości mechanicznych i anizotropii.

EN

Understanding the mechanical properties and their relation to the microstructure of cement paste is crucial for evaluating the performance of existing cementitious materials and for designing new cementitious materials. In this work, a diffusive crack phase field model is applied to multiple-microcrack propagation simulations of cementitious materials with random spherical voids experiencing direct tension. The mechanical properties evaluated using this model are further compared with the characteristics of the lineal-path function, one of the low-order probability functions. Through the analysis, it is found that the lineal-path function can be effective for characterizing the solid phase connectivity in relation to mechanical properties and anisotropy.

2

Effect of Mechanical Activation on the in situ Formation of TiB2 Particulates in the Powder Mixture of TiH2 and FeB

Huynh X.-K., Kim B.-W., Kim J. S.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2B

1393--1398

EN

The in situ formation of TiB2 particulates via an interface reaction between Ti and FeB powders was studied. The effects of mechanical activation by high-energy milling on the decomposition of TiH2 and the interface reactions between Ti and FeB powders to form TiB2 were investigated. Powder mixtures were fabricated using planetary ball-milling under various milling conditions. The specific ball-milling energy was calculated from the measured electrical power consumption during milling process. High specific milling energy (152.6 kJ/g) resulted in a size reduction and homogeneous dispersion of constituent powders. This resulted in a decrease in the decomposition temperature of TiH2 and an increase in the formation reaction of TiB2 particulates in the Fe matrix, resulting in a homogeneous microstructure of nanoscale TiB2 evenly distributed within the Fe matrix. In contrast, the powder mixture milled with low specific milling energy (36.5 kJ/g) showed an inhomogeneous microstructure composed of relatively large Fe-Fe2 B particles surrounded by a thin layer of Fe-TiB2 within a finely dispersed Fe-TiB2 matrix region.

3

A Bayesian virtual metrology for quality inspection of mobile repeater systems

Kim S. D., Kim J. S., Mun B. M., Bae S. J.

Management and Production Engineering Review

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2016

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Vol. 7, No. 4

48--53

EN

The technology of wideband code division multiple access (WCDMA) has been applied to band selective interference cancellation system (ICS) repeaters. To inspect the telecommunication quality of the systems, quality engineers must check the shape of the signals at the corresponding frequency band of the repeaters. However, measuring the signal quality is a repetitive manual task which requires much inspection time and high costs. In the case of small-sized samples, such as the example of an ICS repeater system, Bayesian approaches have been employed to improve the estimation accuracy by incorporating prior information on the parameters of the model in consideration. This research proposes a virtual method of quality inspection for products using a correlation structure of measurement data, mainly in a Bayesian regression framework. The Bayesian regression model derives prior information from historical measurement data to predict measurements of other frequency bandwidths by exploiting the correlation structure of each measurement data. Empirical results show the potential for reducing inspection costs and time by predicting the values of adjoining frequency bandwidths through measured data of a frequency bandwidth in the course of quality inspections of ICS repeater systems.

4

An experimental study on the prediction of back-bead geometry in pipeline using the GMA welding process

Kim J.S., Kim I. S., Lee J.H., Jung S.M.

Archives of Materials Science and Engineering

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2011

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Vol. 49, nr 1

53-61

EN

Purpose: of this research paper is to select optimal welding condition for a root-pass welding for pipeline and to provide a best process for desirable welding quality. Design/methodology/approach: In this study, a variety of welding experiments were carried out to optimize an automated welding process using a GMA (Gas Metal Arc) process, these has been applied for root-pass welding. Welding current, welding speed, wire feed speed and torch angle were chosen as input parameters, while back-bead geometry representing quality of root-pass welding as output parameter. Findings: Based on the results from welding experiments, optimal welding conditions were selected after analyzing correlation between welding parameters and back-bead geometry such as back-bead width and back-bead height. Moreover, not only effectiveness of empirical models developed was compared and analyzed. The optimized empirical models were finally developed for predicting back-bead geometry by analyzing the main effect of each factor and their influence on interaction. Research limitations/implications: This research was concentrated on the developed empirical models that can predict back-bead width and height for root-pass welding in pipeline. Originality/value: This study is intended to define correlations between process parameters and back-bead geometry as welding quality and eventually select optimal welding condition by performing root-pass welding experiment under various conditions.

5

Characteristics of infrared photodiode using SiO₂ insulator on InSb wafer with p-i-n structure

Cho J. Y., Kim J. S., Son S. H., Lee J. H., Choi S. Y.

Opto-Electronics Review

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1999

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Vol. 7, No. 4

369-374

EN

A highly sensitivite photovoltaic infrared diode was fabricated for detecting a 3-5 µm wavelength range in an InSb wafer with a p-i-n structure grown by MOCVD. The formation of silicon dioxide (SiO₂) insulator films for the junction interface and surface of the photodiode were prepared using remote plasma enhanced chemical vapour deposition (PECVD) as InSb has a low melting point and evaporation temperature for surface atoms. The structural characteristics of SiO₂ films and electrical characteristics of metal-insulator-semiconductor structures were initially examined. The leakage current density at 1 MV/cm was about 22 nA/cm², the breakdown electric field of the MIS capacitor using SiO₂ film deposited at 105°C was about 3.5 MV/cm, and the interface-state density at the mid-band gap extracted from the 1 MHz capacitance-voltage measurement was about 2x10¹¹ cm⁻² eV⁻¹. Thereafter, the characteristics of the infrared photodiode were examined. The product of zero-bias resistance by area (R₀A) showed 1.56 x 10⁶ Ωcm² and normalized detectivity exhibited about 1x10¹¹ cm⁻² W⁻¹.