• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.28-33
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• 2008

This paper presents the characteristics of mechanical properties within the heat affected zones(HAZs) of dissimilar metal weld joint between SA508 Gr.1a and F3l6 stainless steel(SS) with Alloy 82/182 filler metal. Tensile tests were performed using small-size specimens taken from the heat affected regions close to both fusion lines of weld, and the micro-structures were examined using optical microscope(OM) and transmission microscope(TEM). The results showed that significant gradients of the yield stress(YS), ultimate tensile stress(UTS), and elongations were observed within the HAZ of SA508 Gr.1a. This was attributed to the different microstructures within the HAZ developed during the welding process. In the HAZ of F316 SS, however, the welding effect dominated the YS and elongation rather than UTS. TEM micrographs demonstrated these characteristics of the HAZ of F316 SS was associated with a dislocation-induced strain hardening.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.3
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• pp.139-145
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• 2004

Equal channel angular pressing (ECAP) technique had been adapted to the Mg alloy (AZ31) for achieving effective grain refinement through severe deformation. The average grain size of $2.5{\mu}m$ could be obtained after 4 passes. The stability of the ECAPed structure at elevated temperatures was examined by annealing the ECAPed materials over a wide range of temperature between 473 and 748 K. The average activation energy, Q, for static grain growth of 1, 2 and 3 passes was 33.7 kJ/mole (=0.25QL, activation for lattice diffusion). The abnormally low Q value in the lower temperature range may indicate that grain growth occurs in the unrecrystallized microstructure where non-equilibrium grain boundaries containing a large number of extrinsic dislocations exist. The yield stresses of the ECAPed alloys decreased whereas the elongations increased after the ECAP process. These results should be related to the modification of texture for easier slip on basal plane.

• Journal of Fashion Business
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• v.14 no.2
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• pp.57-72
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• 2010

The purposes of the research were to find out the clothing construction factors of the mechanical industry working clothes by analyzing the working clothes supplied to 5 subject companies; and to suggest the optimized sewing conditions and the seam strength and elongation experimental data according to the clothing material and seam types implied to the working clothes collected. The fabric types and trimmings used for the mechanical manufacturing working clothes were Polyester/Cotton(65/35%), Polyester/Rayon(65/35%), Cotton(100%); and linings, interlining, various fastenings etc. 2 stitch types, i.e. lock and two-thread chain stitches were applied to the construction of the flat, lap felled, French, superimposed, lapped and bound seams for the seam strength and elongation experiment. The results derived from the experiment were as follows. (1) The seam strength results according to the seam types were high in the order of lap felled>lapped>flat, superimposed and French seams. (2) Considering the features of the seam construction, as the number of fabric layers at the seam line increased the seam strength also increased. (3) Apart from the highest seam strength from the experiment using the net lining with the main fabric, the seam construction consisting of two fabric layers with the interlining showed relatively high seam strength results. (4) The seam elongations according to the stitch types were high in the order of two-thread chain>lock stitches.

• Advanced Composite Materials
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• v.18 no.4
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• pp.351-364
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• 2009

The thermal stability and elevated temperature mechanical properties of $SiC_P$/Al-11.7Fe-1.3V-1.7Si (Al-11.7Fe-1.3V-1.7Si reinforced with SiC particulates) composites sheets prepared by spray deposition (SD) $\rightarrow$ hot pressing $\rightarrow$ rolling process were investigated. The experimental results showed that the composite possessed high ${\sigma}_b$ (elevated temperature tensile strength), for instance, ${\sigma}_b$ was 315.8 MPa, which was tested at $315^{\circ}C$, meanwhile the figure was 232.6 MPa tested at $400^{\circ}C$, and the elongations were 2.5% and 1.4%, respectively. Furthermore, the composite sheets exhibited excellent thermal stability: the hardness showed no significant decline after annealing at $550^{\circ}C$ for 200 h or at $600^{\circ}C$ for 10 h. The good elevated temperature mechanical properties and excellent thermal stability should mainly be attributed to the formation of spherical ${\alpha}-Al_{12}(Fe,\;V)_3Si$ dispersed phase particulates in the aluminum matrix. Furthermore, the addition of SiC particles into the alloy is another important factor, which the following properties are responsible for. The resultant Si of the reaction between Al matrix and SiC particles diffused into Al matrix can stabilize ${\alpha}-Al_{12}(Fe,\;V)_3Si$ dispersed phase; in addition, the interface (Si layer) improved the wettability of Al/$SiC_P$, hence, elevated the bonding between them. Furthermore, the fine $Al_4C_3$ phase also strengthened the matrix as a dispersion-strengthened phase. Meanwhile, load is transferred from Al matrix to SiC particles, which increased the cooling rate of the melt droplets and improved the solution strengthening and dispersion strengthening.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.4
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• pp.440-450
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• 2003

Statement of problem : The joints of removable partial denture alloys have failed frequently after routine usage. Purpose : The purpose of this study was to evaluate the mechanical properties of the laser welded Co-Cr alloys. Material and method : For this study 20 Co-Cr specimens were casted and 10 of them were seperated on the middle area and laser welded with Alpha laser welding machine(Siro Lasertec, Pforzheim, Germany). Rest of them which were as cast, were used as a control group. For the section of the experimental specimens, wire cutting machine was used to make a even gap of the all specimens. Laser welding was done with manufacturer's instrunction and tested each specimen by Instron Machine. Tensile strength, 0.2% yield strength and % elongations were recorded. Fractured surfaces were investigated with SEM. Results : The results were as follows : 1. The tensile strength of the laser welded group(617.7MPa) was about 75% of the as cast group(820.4MPa). It had stastically significant differences(p<0.05). 2. The % elongation of the experimental group was 6.6 which was lower than the control group(14.3). 3. Fracture of the experimental group occured in the welded surface and showed many voids. In contrast, the fracture surface of the control group was showed rough surfaces without any voids. Conclusion : The tensile strengths of the as-cast joints were higher than those for the laser welded joints, and the % elongation of the experimental group was lower than the control group. Porosity was found in laser-welded joints.

• Journal of Ocean Engineering and Technology
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• v.25 no.3
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• pp.53-65
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• 2011

This is the third of several companion papers dealing with the derivation of material constants for ductile failure criteria under hydrostatic stress. It was observed that the ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tended to increase and decrease, respectively, because of the stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that the curves from the two approaches very closely coincide. Failure strains are obtained from the equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress drops suddenly. After introducing the new concept of average stress triaxiality and accumulated average strain energy, the material constants of the Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. The experimental results obtained for EH-36 steel were in relatively good agreement with the 100% critical energy, whereas the literature states that aluminum fits with a 15% critical energy. Therefore, it is expected that a unified failure criterion for critical energy, which is available for most kinds of ductile materials, can be provided according to the used materials.

• The Korean Journal of Ecology
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• v.14 no.4
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• pp.379-398
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• 1991

In order to investigate the ecotypic variations of pulsatilla koreana nakai distributed in korea, 8 local populations of the plant were selected in accordance with latitude and compared on the differences of leaf shape, elongstion, stomatal distribution and dhlorophyll content. The incised angle of the plant is 38。32' in cheju, showing a great difference as compared with 23。77'-30。 32' of the other sites. as to the incised rate, mt. togyu and cheju representsed relatively high values of 49.04% and 48.21% the parted leaved individuals were only observed along the warm current coastal area including cheju, sokcho and sunchon and were 54(62.8%), 2(2.5%) and 3(3.3%) in the sites, respectively. Especially, the individuals consisting of only parted learves were 5(5.8%) in cheju alone and none of the other sites showed such individuals at all. So p. cernua distributed in cheju and p. koreana in inland area can be considered to beecotypic variations of the same species from the upper investigations. According to the elongations of leaf and rachis, the local populations could be classified into 3 types, such as warm current coastal area type(cheju,sunchon and sokcho),southern inland area type(andong, chungju and mt. togyu)and central inland ara type(mt. komdan and hongchon). The dentate numbera of 39.80-43.73 in the warm current area were also different from those of 87% in mt.togyu and 15% in hongchon, while opposite leaflets account for 100% in the other sites. The content of chlorophyll ranged from 0.609 mg/g. d.w.(cheju)to 0.924 mg/g.d.w.(hongchon), showing an increasing trends as the latitudes grow higher. The number of stomata on the low epidermis is much larger than that on the upper epidermis in the whole area. But both aspects showed an increasing tendency, too as the latitude becomes higher.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.703-708
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• 2015

In order to improve the dispersity of nanofiller, polyurethane (PU) nanocomposites were manufactured via poly(propylene gylcol) (PPG) dispersion with MWCNTs prepared by using a ball mill shaker. MWCNTs could be functionalized by treating with the hydrogen peroxide ($H_2O_2$). Tensile strengths and elongations at break of $PU/H_2O_2$ treated MWCNTs nanocomposites were enhanced compared to those of the PU/pristine MWCNTs nanocomposites. The good dispersion of MWCNTs shown in SEM images was obtained by the functionalization of MWCNTs surface. PU/carbon black (CB) composites showed no significant change in the tensile properties. The tensile properties of PU nanocomposites containing pristine MWCNTs or $H_2O_2$ treated MWCNTs were enhanced with increasing dispersion time. As a result, it was certified that the enhanced dispersity of nanofiller brought the improvement of the tensile properties of the MWCNTs based PU nanocomposites.

• The Plant Pathology Journal
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• v.34 no.5
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• pp.403-411
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• 2018

This study takes strawberry-fruits as the test material and discusses the effect of Burkholderia contaminans B-1 on preventing postharvest diseases and inducing resistance-related substances in strawberry-fruits. Soaking and wound inoculating is performed to analyze the inhibitory effects of different treatment solutions on the gray mold of postharvest strawberry-fruits. The count of antagonistic bacteria colonies in the wound is found, and the dynamic growth of antagonistic bacteria and the pathogenic fungus is observed by electron microscopy. The results indicated that, either by soaking/wound-inoculating, the fermentation and suspension of antagonistic bacteria significantly reduced the incidence of postharvest diseases of strawberry-fruits. With wound inoculation, the inhibition rate of antagonist fermentation and suspension ($1{\times}10^{10}cfu/ml$) respectively reached 77.4% and 66.7%. It also led to a significant increase in the activity of resistance-related enzymes, i.e., phenylalanine ammonia lyase (PAL), 4-coumarate coenzyme A ligase (4CL), cinnamate-4-hydroxylase (C4H) and chalcone isomerase (CHI). On 1 d and 2 d post-treatment, the activity of 4CL was respectively 3.78 and 6.1 times of the control, and on 5 d, the activity of PAL was increased by 4.47 times the control. The treatment of antagonistic bacteria delayed the peaking of cinnamyl-alcohol dehydrogenase (CAD) activity and promoted the accumulation of lignin and total phenols. The antagonistic bacteria could be well colonized in the wounds. On 4-5 d post-inoculation, the count of colonies was $10^8$ times of that upon inoculation. Electronmicroscopy indicated that the antagonistic bacteria delayed the germination of pathogenic spores in the wounds, and inhibited further elongations of the mycelia.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.69-84
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• 2002

In this papers, an analytical model which can simulate the post-cracking behavior and tension stiffening effect in a reinforced concrete(RC) tension member is proposed. Unlike the classical approaches using the bond stress-slip relationship or the assumed bond stress distribution, the tension stiffening effect at post-cracking stage is quantified on the basis of polynomial strain distribution functions of steel and concrete, and its contribution is implemented into the reinforcing steel. The introduced model can be effectively used in constructing the stress-strain curve of concrete at post-cracking stage, and the loads carried by concrete and reinforcing steel along the member axis can be directly evaluated on the basis of the introduced model. In advance, the prediction of cracking loads and elongations of reinforced steel using the introduced model shows good agreement with results from the previous analytical studies and experimental data.