• Advances in concrete construction
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• v.15 no.3
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• pp.191-202
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• 2023

Palm oil fuel ash (POFA) is a newly emerging pozzolanic material having high amount of silica content. Various forms of POFA were used in cement-based materials (CBMs) in replacement of cement in different dosages of low and high volume. Although, there are many researches on POFA to be used in concrete and mortar, however, this material was not practically used in the construction industry. Engineers and designers need to be confident to use any new developed materials by knowing all engineering properties at short and long terms. As durability concern, concrete pH value is one of the most important properties. Portland cement produces are alkaline initially, however, it may be reduced due to aging and its components. It is believed that by incorporation of supplementary cementitious materials in CBMs the pH value reduces due to utilization of Ca(OH)₂ in pozzolanic reaction. This study is the first attempts to understand the pH value of mortars containing up to 30% POFA under different curing conditions and its changes with time. The results were also compared with the pH of ground granulated ballast furnace slag (GGBFS) and fly ash (FA) content mortars. In addition, the compressive strength of different mortars under different curing conditions were also studied. The results showed that the pH value of control mix (without cementitious materials) was more than all the blended cement mortars indifferent curing conditions at the same ages. However, there was a reducing trend in the pH value of all mortar mixes containing POFA.

• Composites Research
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• v.27 no.2
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• pp.52-58
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• 2014

Short fiber reinforced composites manufactured by injection molding have diverse fiber orientations variable with measuring positions even in the same specimen, which is caused by the flow induced fiber orientation. Fiber orientations considerably affect the mechanical and thermal properties of final composite products. In this study, fiber orientation of injection molded carbon fiber reinforced PA6/PPO composite was measured at several points of the specimen by optical microscopy analysis and the corresponding izod impact strength, coefficients of thermal expansion (CTE) were also measured to investigate the influence of local fiber orientation on the mechanical and thermal properties. Izod impact strength where fiber was perpendicular to the direction of crack propagation was higher than where fiber was parallel to the direction, which could be explained be the impact resistance reinforcing mechanism by fiber orientation. CTE was also lower where fiber was parallel to the measurement direction of CTE than where fiber was perpendicular to the direction, which could be also explained by the dimensional stability mechanism by fiber orientation.

• Macromolecular Research
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• v.15 no.4
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• pp.315-323
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• 2007

The present manuscript deals with the prediction of the lifetime of NBR compound based rubber gaskets for use as fuel cells. The material was investigated at 120, 140 and $160^{\circ}C$, with aging times from 3 to 600 h and increasing $H_2SO_4$ concentrations of 5, 6, 7 and 10 vol%. Both material and accelerated acid-heat aging tests were carried out to predict the useful life of the NBR rubber gasket for use as a fuel cell stack. To investigate the effects of acid-heat aging on the performance characteristics of the gaskets, the properties of the NBR rubber, such as crosslink density and elongation at break, were studied. The hardness of the NBR rubber was found to decrease with decreasing acid concentration at both $120\;and\;140^{\circ}C$, but at $160^{\circ}C$, the hardness of the NBR rubber increased abruptly in a very short time at different acid concentrations. The tensile strength and elongation at break were found to decrease with increases in both the $H_2SO_4$ concentration & temperature. The observed experimental results were evaluated using the Arrhenius equation.

• The Research Journal of the Costume Culture
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• v.21 no.6
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• pp.967-973
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• 2013

During high speed sewing, the needle thread is exposed to dynamic loading, short strike loading, inertia forces, friction, rubbing, force of check spring, bending, pressure, friction, impact, shock and thermal influence. The dynamic thread loading/tension alters throughout the stitch formation cycle and along its passage through the machine. The greatest tensile force occurs at the moment of stitch stretching, when the take up lever pulls for required thread length through the tension regulator. These stresses act on the thread repeatedly and the thread passes 50-80 times through the fabric, the needle eye and the bobbin case mechanism, before getting incorporated into the seam, which result in upto 40% loss in tensile strength of the sewing thread. This damage in the sewing thread adversely affects its processing and functional performance. In this paper, the contribution of dynamic loading, passage through needle and fabric, and bobbin thread interaction in the loss in tensile properties has been studied. It is observed that the loss in tensile properties occurs mainly due to the bobbin thread interaction. Dynamic loading due to the action of take up lever also causes substantial loss in tenacity and breaking elongation of cotton threads.

• The Korean Journal of Community Living Science
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• v.25 no.3
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• pp.383-388
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• 2014

This study was examined the physical characteristics (geometry, yield strength, thousand-seeds weight, true density, and moisture content) required for mechanization-related technologies such as (harvesting, washing, transport, and drying). Large differences in the size and shape of boxthorn berries(Jangmyeong, Bullo, Chungmyeong, and Hokwang) are used to analyze these physical properties. The average diameter, volume, surface area, and sphericity rate are calculated using long and short diameters of the boxthorn berry according to its variety. Hokwang has the largest measured surface area, and Bullo, the smallest. Average yield strength is 1.78 kPa and the mechanical pressure of soft boxthorn berries is not more than 1 kPa. Bullo has the highest true density. The optimum drying time for the measurement of moisture content is 4 hours at the drying temperature of $100^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.199-202
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• 2006

In this study, SiC whiskers were grown on a porous SiC diesel particulate filter for nanoparticle filtering. To grow the whiskers at the inner pore without closing the pores, we used chemical vapor infiltration with a solution source and a dilute. As the deposition time increased, the whiskers grew and formed a network structure. After 180 min of deposition, the mean diameter of the whiskers was 174 nm and the compressive strength was 58.4 MPa. The pores shrank from $10{\mu}m\;to\;0.4{\mu}m$ and, because the whiskers filed the inner pores, the gradient of permeability decreased as the deposition time increased. However, by using the network structure of whiskers deposited for 120 min and 180 min, we obtained a diesel particulate filter with pores of $0.98{\mu}m\;and\;0.4{\mu}m$, respectively. Furthermore, the filter shows better permeability than a porous body with pores of $1{\mu}m$. In short, by filtering the nanoparticulate materials, the network structure of whiskers improves the strength, reduces the pore size and minimizes the permeability drop.

• Earthquakes and Structures
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• v.10 no.3
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• pp.699-716
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• 2016

Buckling-restrained braced frames (BRBFs) are commonly used as lateral force-resisting systems in the structures located in seismic-active regions. The nearly symmetric load-displacement behavior of buckling-restrained braces (BRBs) helps in dissipating the input seismic energy through metallic hysteresis. In this study, an experimental investigation has been conducted on the reduced-core length BRB (RCLBRB) specimens to evaluate their hysteretic and overall performance under gradually increased cyclic loading. Detachable casings are used for the concrete providing confinement to the steel core segments of all test specimens to facilitate the post-earthquake inspection of steel core elements. The influence of variable core clearance and the local detailing of casings on the cyclic performance of RCLBRB specimens has been studied. The RCLBRB specimen with the detachable casing system and a smaller core clearance at the end zone as compared to the central region exhibited excellent hysteretic behavior without any slip. Such RCLBRB showed balanced higher yielding deformed configuration up to a core strain of 4.2% without any premature instability. The strength-adjustment factors for the RCLBRB specimens are found to be nearly same as that of the conventional BRBs as noticed in the past studies. Simple expressions have been proposed based on the regression analysis to estimate the strength-adjustment factors and equivalent damping potential of the RCLBRB specimens.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.308-311
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• 2012

A wide range of possible hazards existing in thermal batteries are mainly caused by thermal runaway, which results in overheating or explosion in extreme case. Battery separators ensure the separation between two electrodes and the retention of ion-conductive electrolytes. Thermal runaways in thermal batteries can be significantly reduced by the adoption of these separators. The high operating temperature and the violent reactivity in thermal batteries, however, have limited the introduction of conventional separators. As a substitute for separators, MgO powders have been mostly used as a binder to hold molten salt electrolyte. During recent decades the fabrication technology of ceramic fiber, which has excellent mechanical strength and chemical stability, has undergone significant improvement. In this study we adopted wet-laid nonwoven paper making method instead of the electrospinning method which is costly and troublesome to produce in volume. Polymeric precursor can readily be coated on the surface of wet-laid ceramic paper, and be formed into ceramic film after heat treatment. The mechanical strength and the thermo-chemical stability as well as the wetting behaviors of ceramic separators with various molten salts were investigated to be applicable to thermal batteries. Due to their excellent chemical, mechanical, and electrical properties, wet-laid nonwoven separators made from ceramic fibers have revealed positive possibility as new separators for thermal batteries which operate at high temperature with no conspicuous sign of a short circuit and corrosion.

• Korean Journal of Materials Research
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• v.33 no.6
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• pp.251-256
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• 2023

This study aims to examine the correlation between microstructures and the mechanical properties of two high-strength API X70 linepipe steels with different specimen directions and Moaddition. The microstructure of the Mo-added steel has an irregularly shaped AF, GB matrix with pearlite because of the relatively large deformation in the non-recrystallization temperature region, while that of the Mo-free steel shows a PF matrix with bainitic microstructure. In the Mo-added steel, the M/A (martensite-austenite) in granular bainite (GB) and pearlite act as crack initiation sites with decreased upper shelf energy and an increased ductile to brittle transition temperature (DBTT). Regardless of Mo addition, all of the steels demonstrate higher strength and lower elongation in the T direction than in the L direction because of the short dislocation glide path and ease of pile-up at grain boundaries. In addition, the impact test specimens with T-L direction had a lower impact absorbed energy and higher DBTT than those with the L-T direction because the former exhibit shorter unit crack path compared to the latter.

• Journal of Korea Entertainment Industry Association
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• v.13 no.1
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• pp.185-197
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• 2019

This study intended to analyze the early childhood education freshmen's academic interest. For this study relationship among academic self-efficacy, character strength and learning motivation. The study subjects were 144 early childhood education freshmen at K-college in Deagu. They answered the survey regarding academic self-efficacy scale, VIA-IS(Values in action inventory of strength) short form scale, school learning motivation scale. The collected data were analyzed by frequency analysis, descriptive statistics, pearson correlation and multiple regression analysis using SPSS 18.0 program. The study finding are as follows. First, the average of academic self-efficacy, character strength and learning motivation of students were near at the intermediate-level. Second, academic self-efficacy, character strength and learning motivation were significantly positive correlated. Third, when examining the relative effect of early childhood education freshmen's academic self-efficacy and character strength on learning motivation, self regulatory efficacy among the sub-factors for academic self-efficacy and courage among the sub-factors for character strengths.