• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.05a
• /
• pp.57-58
• /
• 2006

The effects of lowering ECAP temperature during ECAP process and Post-ECAP annealing on microstructure, texture and mechanical properties of the AZ31 alloys have been investigated in the present study. The as-extruded materials were ECAP processed to 2 passes at 553K prior to subsequent pressing up to 6 passes at 523K or 493K. When this method of lowering ECAP temperature during ECAP was used, the rods could be successfully deformed up to 6 passes without any surface cracking. Grain refinement during ECAP process at 553K might have helped the material to endure further straining at lower deformation temperatures probably by increasing the strain accommodation effect by grain boundary sliding, causing stress relaxation. Texture modification during ECAP has a great influence on the strength of Mg alloys because HCP metals have limited number of slip systems. As slip is most prone to take place on basal planes in Mg at room temperature, the rotation of high fraction of basal planes to the directions favorable for slip as in ECAP decreases the yield stress appreciably. The strength of AZ31 Mg alloys increases with decrease of grain size if the texture is constant though ECAP deformation history is different. A standard positive strength dependence on the grain size for Mg alloys with the similar texture (Fig. 1) supports that the softening of ECAPed Mg alloys (a negative slope) typically observed despite the significant grain refinement is due to the texture modification where the rotation of basal planes occurs towards the orientation for easier slip. It could be predicted that if the original fiber texture is restored after ECAP treatment yielding marked grain refinement, yield stress as high as 500 MPa will be obtained at the grain size of ${\sim}1{\mu}m$. Differential speed rolling (DSR) with a high speed ratio between the upper and lower rolls was applied to alter the microstructure and texture of the AZ31 sheets. Significant grain refinement took place during the rolling owing to introduction of large shear deformation. Grain size as small as $1.4{\mu}m$ could be obtained at 423K after DSR. There was a good correlation between the (0002) pole intensity and tensile elongation. This result indicates that tensile ductility improvement in the asymmetrically rolled AZ31 Mg alloys is closely related to the weakening of basal texture during DSR. Further basal texture weakening occurred during annealing after DSR. According to Hall-Petch relation shown in Fig. 1, the strength of the asymmetrically rolled AZ31 is lower than that of the symmetrically rolled one when compared at the same grain size. This result was attributed to weakening of fiber texture during DSR. The DSRed AZ31, however, shows higher strength than the ECAPed AZ31 where texture has been completely replaced by a new texture associated with high Schmid factors.

• Journal of the Korea Concrete Institute
• /
• v.16 no.1 s.79
• /
• pp.27-35
• /
• 2004

Most of concrete fatigue tests currently used are flexural tension or compression methods to investigate the tensile or compressive properties, respectively. However, the concrete pavement or concrete slab is actually subjected to a combined stress condition such as biaxial or triaxial. The split tension test may result in similar stress condition to biaxial stress condition. The purposes of this study were to evaluate the split tension fatigue test method for application in concrete. These were done by a finite element analysis and experimental series. The results were as follows: The optimum configuration of split tension fatigue test was a cylinder of 15cm in diameter and 7.5cm in thickness, which had a little different thickness compared to the KS standard cylinder of ${\phi}15{\times}30cm$. The concrete stress ratio of compressive against horizontal from FEA was 3.1, while that from theory was 3.0. The stress distributions of mortar and steel were almost similar at different thicknesses. The measured static split tensile strengths of concrete and mortar were quite similar at 30cm and 7.5cm thickness cylinders. The measured stress-strain relationship showed their consistency at all specimens regardless of thickness, and confirmed the results from FEA. As a results, the concrete split tension specimen, cylinder of 15cm in diameter and 7.5cm in thickness, could be used at fatigue test because of its accuracy, simplicity and convenience.

• Journal of the Korea Concrete Institute
• /
• v.21 no.6
• /
• pp.719-727
• /
• 2009

The requirements of the maximum shear reinforcement in the EC2-02 and CSA-04, which are developed based on the truss model, are quite different to those in the ACI-08 code and AIJ-99 code, which are empirical equations. The ACI 318-08, CSA-04, and EC2-02 codes provide an expression for the maximum amount of shear reinforcement ratio as a function of the concrete compressive strength, but Japanese code does not take the influence of the concrete compressive strength into account. For high strength concrete, the maximum amount of shear reinforcement calculated by the EC2-02 and CSA-04 is much greater than that calculated by the ACI 318-08. Ten RC beams having various shear reinforcement ratios were tested and their corresponding shear stress-shear strain curves and failure modes were compared to the predicted ones obtained by the current design codes.

• The Journal of Korean Academy of Prosthodontics
• /
• v.36 no.6
• /
• pp.858-866
• /
• 1998

Soldering is the usual method used to correct an unstable fixed partial denture framework at patient's try-in; However, presoldering base metal alloys is technique-sensitve and results are unstable because it is difficult to maintain uniform heat distribution and to prevent oxidation of an alloy. A cast-joining technique has been developed by Weiss and Munyon for repair, correction and addition to base metal framework. This joining technique eliminates the problem with presoldering of non-precious frameworks. The object of this study was to 1) compare the relative flexure strength and the joining effectiveness of Ni-Cr-Be cast in two pieces and 'pre-soldered' versus in two pieces and 'cast-joined'. 2) determine the effect of increasing the number of retentive grooves on the face of the cast and 3) determine the effect of the relative matched position of groove patterns on flexure strength. The joining effectiveness can be expressed by the ratio of the mean flexure stress of soldered or cast-joined specimens to that of one-piece cast. Resin rods 3mm in diameter were used as pattern of specimens for one-piece casted, presoldered, and cast-joined groups. Cast-joined specimens had two different patterns of retentive grooves on the joined faces. Type A had cross-shaped grooves 1mm in depth. 0.6mm in width. Type B was the same except for the addition of one more retentive groove. In the experiment connecting cast-joined specimens, half of specimens with type A pattern had their patterns on the faces of paired casts matched with each other as mirror image. With the rest pairs, it was proceeded that one of paired casts turned 45 degrees so that the patterns crossed. Half of specimens with type B pattern also had the patterns matched as mirror image; However, here, one of paired casts turned 90 degrees with the other pairs. Retentive groove in this study lacked the intentional undercuts, in contrast with the suggestion of Weiss and Munyon. The specimens were subjected to four-point flexural loading in an Instron testing machine. The midspan flexural stress was calculated at the point of initial plastic strain as determined from a strip-chart recorder or at the point of failure if this occured at a lower stress level. Within the scope of this study, the following results were obtained. 1. The presoldered group showed flexural strength at least 2 times higher than the cast-joined groups. Its joining effectiveness was 82%. 2. In cast-joined groups, the flexural strength of joints with type B patterns exhibited 1.5 times that of joints with type A patterns. Joining effectivenesses were 38% for type B patterns, 25-26% for type A patterns. 3. The relative matched position of groove patterns did not have any significant effect on flexural strength of the cast-joined specimens with either type A patterns or type B patterns(p>.05).

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.33 no.1
• /
• pp.91-100
• /
• 2004

Weanling male rats of Wistar strain were fed relatively high-calories-diet containing 1% (K$_1$ group), 5% (K$_{5}$ group) and 10% Chinese cabbage kimchi juice (K$_{10}$ group) for 4 weeks to study their effects on body weight gain rate, serum lipids levels and other blood biochemical parameters. In this study it was found out that significant decrease in body weight gain rate, diet efficiency ratio, serum triglyceride level, serum total cholesterol level, blood glucose level and LDL-cholesterol level was observed in $K_{10}$ group as compared to control group fed only high-calories-diet. Significant increase in HDL-cholesterol level, GPT activity, GOT activity and creatinine level was found in $K_{10}$ group as compared to control group. But creatinine level, GPT and GOT activity of $K_{10}$ group were within the normal ranges. The results suggest that long term intake of traditional Chinese cabbage kimchi in large dose have the lowering effect on blood lipid and blood glucose level. There is no possibility of adverse actions on renal and hepatic functions by ordinary intake of Chinese cabbage kimchi in spite of being rich in salt and hot spices such as garlic, onion, ginger and red pepper.r.r.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.27 no.3
• /
• pp.1-17
• /
• 1999

The purpose of this study is to evaluate the creation techniques of artificial wetland, one of biotopes developed to promote biodiversity in urban areas, and to look for improvement steps. Specifically, artificial wetland creation techniques were categorized into living environment and living creature classification. Being living conditions for creations, habitat environment was reviewed with a focus on water and soil environments. Living creatures were classified into plants, insects, fish, and birds. The evaluation of creation techniques was done in post-construction evaluation while considering the creation of habitats for living creatures. Intervention by users, changes in living environment and living species, and relevance of creation techniques were reviewed. Key results of this study are as follows. (1) Water environment for the living environment of creatures provides a suitable environment conditions for the living of creatures through a process easing the use of piped water. Various water depths and embankment appear to have a positive impact on the living of aquatic life. In particular, embankment covered in soil naturally played an important role as a place for the activities of aquatic insects and young fish as well as the growth of aquatic plants. (2) Various aquatic and ground plants to promote insect-diversity, shallow water, and old-tree logs had contributed greatly in increasing the types and number of insects. Aquatic insects. Aquatic insects were seen much particularly in areas where aquatic plants are rich but water is shallow than any other areas. (3) A space piled with stone to provide habitats for fish was not much used. However, it was observed that fish used embankment built with natural stones and embankment using logs in areas where water is deep. In addition, it was confirmed that 1,500 fish that had been released propagated using various depths and places for birth. (4) It was analyzed that techniques (creation of island, log setting, and creation of man-made bird nests) to provide habitats and to attract birds are not serving their roles. In such a case, it is believed that species had not increased due to the smallness as well as isolated features of the area. Based on theoretical review, they are judged to be areas that are likely to be used when a greater variety of birds is introduced. It is judged that attracting and keeping more birds at the site, such spaces need to be linked systematically in the future in terms of building eco-network while ensuring an adequate living areas. (5) In the study areas, users intervened greatly. As a result, a blockage was created preventing the normal growth of plants and non-indigenous plants were introduced. In order to limit the intervention by users, setting enough buffer zones, and environment education programs were urgently required. D/H=1>Hyangkyo> houses on the river>temples>lecture halls. D/H ratio of the backside areas is as follows. D/H=1>Hyangkyo>houses on the river>lecture halls. 4. Inner garden were planted deciduous than evergreen trees with Lagerstroemia indica. Enclosed dominant trees were planted by Pinus densiflora, Querces seuata. construct GEM strain, and examined for the expression and functional stability in microcosms.

• Journal of the Korea Concrete Institute
• /
• v.28 no.3
• /
• pp.289-298
• /
• 2016

An experimental research was performed using fibers for the purpose of retrofitting existing reinforced concrete circular columns. Glass fiber (GF) and polyethylene terephthalate (PET) were used as well as combined GF+PET (HF). PET has high tensile strength (over 600 MPa) and high ductility (about 15%), but has very low elastic modulus (about 1/6 of GF). A total of four columns was tested against laterally applied reverse cyclic load: control column, GF-, PET-, and HF-strengthened columns. All columns retrofitted using fibers demonstrated improved moment capacity and ductility. Moment capacity of GF-, PET-, and HF-strengthened columns was 120%, 107%, and 120% of the control column, respectively. Drift ratio of all retrofitted columns also increased by 63 ~ 83% over the control column. The final failure mode of the control column was main bar buckling. The final failure mode of the GF- and HF-strengthened columns was GF rupture while that of the PET-strengthened column was main bar rupture in tension. No damage was observed for PET at the ultimate stage due to excellent strain capacity intrinsic to PET. Current test results indicate that PET can be effectively used for seismic retrofit of RC columns. It is noted that the durability characteristics of PET needs to be investigated in the future.

• Korean journal of applied entomology
• /
• v.34 no.4
• /
• pp.328-333
• /
• 1995

Susceptibilies of tow-spotted spider mite (Tetranychus urticae Koch) collected at 6 locations were assessed to 15 acaricides. The response to acaricides were almost similar in female adults and eggs. There were considerable difference in susceptibility depending on the acaricide treated and the region from which the population was collected. The population showing resistance ratio of more than 20 with respect to certain acaricide was regarded as a resistant population to the acaricide. The resistant populations in terms of female adult were as follows: Suwon population to azocyclotin, cyhexatin, and fenbutatin-oxide; Taejon population to dicofol and fenbutatin-oxide; Chongju population to dicofoll Chinju populatin to cyhexatin, dicofol, and fenbutatin-oxide. The resistant populations in terms of egg were as follows; Suwon population to bifenthrin, clofentezine, hexythiazox, and tetradifon; Kunwi, Chongju, and Kwangju populations to bifenthrin; Taejon population to amitraz and bifenthrin; Taejon populatin to amitraz and bifenthrin; Chinju population to amitraz, bifenthrin, clofentezine, dicofol, and tetradifon. However, the female adults and eggs of all field populations were susceptible to abamectin, chlorfenson, and fenpyroximate. This tendency was also reported previously in the susceptible strain from laboratory.

• Korean journal of applied entomology
• /
• v.28 no.1
• /
• pp.16-22
• /
• 1989

A series of experiments was undertaken to learn bionomics and gowt plant resistance of the seedcorn maggot, Delia platura(Meigen), under controlled(24$\pm$$2^{\circ}C$, RH70$\pm$5%, and LD 16:8h)and field conditions. The preoviposition period for the flies was 9 days. The females survived for an average of 50(3-77) and the males for 24(1-59) days. A greater proportion of flies emerged between 6:00 A.M. and 9:00 A.M., soon after the sun rise. After the over-wintering, adults started to emerge in mid-April from pupae located near the soil surface, and peaked in late April by others located deeper. The sex ratio was about 1:1 with total samples of 1,609 females and 1,641 males. Weight of pupae reared from onion was heavier than those from other diets in the laboratory, however its size was samller than that of natural flies. Considerably more eggs were laid near pea seeds than other hosts tested. Among beans, Bapmitkong with blue seed-coat and a cowpea bean strain were preferred for oviposition. 'Namcheon` cultivar was found to be susceptible to attack by the larvae in the laboratory.

• Journal of Korea Foresty Energy
• /
• v.24 no.2
• /
• pp.31-36
• /
• 2005

Cauliflower mushroom (Sparassis crispa) is an edible mushroom that shows remarkably high contents of $1,3-{\beta}-D-glucan$ compared to other edible mushrooms. The mushroom is known to give high antitumor and immunologic activities, thus the mushroom is recently cultivated in Japan and Korea. However, cultivation methods are being kept in secret or under patents by some companies with complicated procedures. This study was conducted to solve the problem by providing a simple method for the cultivation of cauliflower mushroom. We could produce the mushroom using sawdust-based media of Larix leptolepis, Pinus densiflora and P. koraiensis with addition of barley flours and sugar. The ratio of the sawdust : barley flours : sugar used for this study was 80:20:3 in dry-weight base, and the water content was adjusted as 65%. The productivity was somewhat different among the species of sawdust media and the strains of Sparassis crispa for the cultivation, and the mushroom production reached up to 177g from 650g base(productivity : 27%). Thus, this medium is strongly recommended as a practical cultivation method for cauliflower mushroom. By the way, further study for the determination of adequate concentration of barley flour and the selection of proper strain for each sawdust species is needed.