• Transactions of Materials Processing
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• v.33 no.3
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• pp.161-168
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• 2024

Aluminum alloy sheets, compared to conventional steel sheets, face challenges in press forming due to their lower elongation. To enhance their formability, extensive research has focused on forming technologies at elevated temperatures, specifically warm forming at around 300℃ and hot forming at approximately 500℃. This study proposes that the formability of aluminum alloy sheets can be significantly enhanced using a multi-stage hot forming technique. The research also investigates whether the strength of the A6061 aluminum alloy, known for its precipitation hardening, can be maintained when formed below the precipitate solid solution temperature. In the experiments, the A6061-T6 sheet underwent heating and rapid cooling between 250 and 500℃. The mechanical properties were evaluated at each stage of the process. The findings revealed that when the initial heat treatment was below 350℃, the strength of the material remained unchanged. However, at temperatures above 400℃, there was a noticeable decrease in strength coupled with an increase in elongation. Conversely, when the secondary heat treatment was conducted at temperatures of 350℃ or lower, the strength remained comparable to that of the initial heat treated material. However, at higher temperatures, a reduction in strength and an increase in elongation were observed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.4 s.56
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• pp.116-125
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• 2009

Recently, modular system are popular in construction fields, and they are increasing their marcket share. To compare modular units, bolting and welding are most popular methods. However, the temperature around a welded part might be over than 1,300$^{\circ}C and the composite member might be exposed tp the direct welding heat about 20,000$^{\circ}C. This high welding heat makes decrease of the concrete strength. If the concrete strength seriously decreases, it can affect the behavior and safty of a structure. On this study, To prevent of concrete strength decreases by welding heat, we suggested method of to insert between steel and concrete.

• Korean Journal of Veterinary Research
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• v.50 no.2
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• pp.93-103
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• 2010

This study investigated the potential effects of amitraz on the pre- and postnatal development, behavior, and reproductive performance of offspring of parent rats given amitraz during pre-mating, gestation, and lactation. The test chemical was administered via the drinking water containing 0, 40, 120, and 360 ppm to male rats from 2 weeks before mating to the end of 14-day mating period and to females from 2 weeks before mating, throughout mating, gestation and lactation up to weaning. Based on fluid consumption, the male rats received an average of $0,\;5.7{\pm}1.33,\;13.2{\pm}2.08,$ and $35.8{\pm}3.42$ mg/kg/day amitraz, and the female rats received an average of $0,8.7{\pm}4.42,\;20.1{\pm}9.60,\;and\;47.6{\pm}22.38$ mg/kg/day amitraz, respectively. At 360 ppm, an increase in the incidence of abnormal clinical signs, a suppression in the body weight gain, a decrease in the food consumption and litter size, an increase in the post-implantation loss, and a decrease in the seminal vesicle weight were observed in the parent animals. In addition, a suppression in the body weight gain, a decrease in the grip strength, a delay in the negative geotaxis, an increase in the pre- and post-implantation loss, and a decrease in the number of live embryos were observed in the offspring. At 120 ppm, suppressed body weight gain and reduced food consumption were observed in the parent rats. Suppressed body weight gain and decreased grip strength were also observed in the offspring. There were no signs of either reproductive or developmental toxicity at 40 ppm. Under these experimental conditions, the no-observed-adverse-effect level of amitraz for parent rats and their offspring was estimated to be 40 ppm in rats.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.9
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• pp.643-653
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• 2013

In this study, trend analysis was performed by various runoff analysis method of Non-point Pollution Source(NPS) at the impervious area. The characteristics of rainfall at impervious area appeared to be influenced by rainfall strength and it appeared that first flush phenomenon occurs often if rainfall strength acts largely. It is judged that the measure is required to be prepared against that now that concentration difference of non-point pollution source appeared to be big by precedent number of days of no rainfall. As the result of calculating Decrease Rate (DR) by first flush of non-point pollution source, it is judged that it is important to prepare the measure against the pollutants about initial rain and it is necessary to calculate the capacity of non-point pollution source processing facilities regarding that now that the non-point pollution source integrated at impervious area showed the characteristics that are flowed out in high concentration by initial rain in case of non-rainfall considering the characteristics of non-point pollution source at impervious area. When taking 50% of non-point pollution source as the standard for decrease rate that was evaluated previously, it appeared as 15~60 min in case of TSS and it appeared as 30~90 min in case of organic compound, but the characteristic whose decrease rate is below 50% also appeared even till rainfall-runoff ends. Based on that, it is judged that it could be used as the reference when designing the structural BMPs facilities later.

• Journal of the Korean Wood Science and Technology
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• v.45 no.5
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• pp.535-543
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• 2017

For column-beam gussets of wooden structures, slit-processed members inserted with a steel plate are used in general. In this study, a rigid portal frame bonded with a joint was fabricated and a semi-rigid portal frame was fabricated by making a wooden gusset, a replacement for steel plate, of which a half was integrated into the column member and the other half was joined with the beam member by drift-pins. The lateral strength performance of the wooden portal frame was compared with that of the steel plate-inserted joint portal frame. The lateral strength performance was evaluated through a perfect elasto-plasticity model analysis, sectional stiffness change rate, and short-term permissible shear strength. As a result of the experiment, the maximum strength of the rigid portal frame was lower than that of the steel plate-inserted joint portal frame. The yield strength and ultimate strength were calculated as 0.58 and 0.48, respectively, but the measurements of initial stiffness and cumulative ductility improved by 1.35 and 1.1, respectively. As a result of the perfect elasto-plasticity model analysis of the semi-rigid portal frame, the maximum strength was lower than that of the rigid portal frame, but the toughness after failure was excellent. Thus, the ultimate strength was higher by 1.05~1.07. The steel plate-inserted portal frame showed rapid decrease in stiffness with the progress of repeated tests, but the stiffness of the portal frames with a wooden joint decreased slowly.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.9-15
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• 2010

Recently, the high-compressive strength concrete where the use is extending was weak in fire because of spalling that was occurring with rise of internal vapor pressure by high temperature. For preventing spalling of high-strength concrete in fire, Organic fibers have been using in concrete generally. By melting of organic fibers in concrete in fire, the internal moistures of concrete moves quickly to the outside, and so, preventing of spalling of high-strength concrete. But this method will be able to prevent the spalling of high-strength concrete, but makes the decrease of the concrete strength after fire. This study make a comparison between properties of preventing of spalling and remaining compressive strength of concrete using intumescence Alkali-Silicates fire-resistant material and that of concrete with organic fibers. Using organic fibers for preventing of spalling of concrete are P.P and Nylon fibers, and anti-fire intumescence material for protection of concrete surface is alkali-silicate materials. Fire resistance test executed as long as 3 hr under the flame temperature $1,200^{\circ}C$ over. In the case of concrete with P.P fibers, don't occurred the spalling, but the remaining compressive strength will not be able to measure, the concrete using intumescence Alkali-Silicates system fire-resistant material is not only preventing of the spalling but also the remaining compressive strength maintained until the maximum 96%.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.621-630
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• 2006

Twelve beams made of lightweight high-strength concrete were tested to determine their diagonal cracking and ultimate shear capacities. A total of 12 beams without(4 beams) and with lightweight(8 beams) were tested in a stiff testing facility, and complete load-midspan deflection curves, including the maximum capacities portion, were obtained. The variables in the test program were concrete strength, which varied 35.4 MPa, 65.3 MPa; shear span-depth ratios a/d=1.5, 2.5, 3.5, 4.5; and tensile steel ratio between 0.57 and 2.3 percent. Also, we divided beam by diagonal tension crack and ultimate shearing strength to propose an equation. In addition, it analyzed comparison mutually applying existing proposal and guide. $V_{cr}$ was as result that AIK recommendations and Zsutty proposal decrease more than a/d=2.5, increased some in Mathey's proposal equation. $V_{cr,\exp}/V_{cr,cal}$ showed tendency of overestimation according to increase of tensile steel ratio and compressive strength of concrete. On the other hand, $V_{cr,\exp}/V_{cr,cal}$ is superior in conformability with an experiment result Zsutty's proposal among other equations. The proposal equation hew that expect $V_{cr}/V_u$, rationally about shearing strength. Therefore, shear strength an equation is considered to be utilized usefully evaluating capacity by change of the shear span depth ratio of lightweight concrete, tensile steel ratio, and compressive strength of the concrete in this research.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.613-620
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• 2013

Concrete has been recognized as a material which is resistant to high temperatures, but chemicophysical property of concrete is changed by the high temperature. So, mechanical properties of concrete may be reduced. Because of this, standards and researches on the degradation of the mechanical properties of concrete at high temperatures have been presented. However, research data about the state that considering the loading condition and high-strength concrete is not much. Therefore, this study evaluated the high-temperature properties of high-strength concrete by loading condition and elevated temperature. The stress-strain, strain at peak stress, compressive strength, elastic modulus, thermal strain and the transient creep are evaluated under the non-loading and $0.25f_{cu}$ loading conditions on high strength concrete of W/B 12.5%, 14.5% and 20%. Result of the experiment, decrease in compressive strength due to high temperature becomes larger as the compressive strength increases, and residual rate of elastic modulus and compressive strength is high by the shrinkage caused by loading and thermal expansion due to high temperature are offset from each other, at a temperature above $500^{\circ}C$.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.33-40
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• 2018

Currently, in South Korea, because of reducing the construction period or treating wasted water, there are some cases of missing wet curing for concrete structure even though for high strength concrete. This air curing conditions is considered to cause increased possibility of compressive strength decrease, and increasing drying or autogenous shrinkages. As a solution of shrinkage of concrete, The authors' research team conducted the research on improving durability of concrete with decreasing autogenous shrinkage by adding the oil or fat to induce the saponification. Therefore, in this research, the influence of curing method on compressive strength, shrinkage on evaporation rate of high strength mortar including high volume supplementary cementitious materials (SCMs) was evaluated depending on various curing methods such as air curing, drying after painting emulsified refined cooking oil (ERCO), and drying after 7 and 28 days' wet curing. The experimental result showed the air curing method caused approximately 50% of decreased compressive strength and 1.9 times of increased shrinkage rather than the 28-day-wet curing method, thus it was known that the wet curing significantly influences on performance of high strength mortar using high volume SCMs. However, the ERCO painting curing caused decreased performance of concrete rather than drying after 7 days curing while it caused improved performance of concrete than entire period air curing.

• Korean Journal of Environmental Agriculture
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• v.7 no.2
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• pp.96-101
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• 1988

It is important to assess the effects of ionic strength and type of anions when studying the adsorption of heavy metals on zeolite because the background salt may complex with heavy metals and compete for adsorption sites. This experiment was carried out to determine the effect of ionic strength and anion species($Cl^-$, $SO^{2-}\;_4$, and $ClO^-\;_4$) on heavy metal adsorption. Heavy metal adsorption by zeolite from solutions in the range of 10 to 50ppm was studied in the presence of NaCl, $Na_2SO_4$ and $NaClO_4$, with different concentrations. The ionic strength ranged from 0.01 to 1.00. Adsorption of heavy metal cations could be described by the Freundlich isotherm equation. Increasing the ionic strength of equilibrium solutions, the amounts of heavy metal adsorbed on the zeolite surfaces decreased in all three of the anion systems. This fact could be attributed to the competition of background salt cation and the decrease in initial activity of heavy metal cations. In the presence of Cl anion, less adsorption resulted than in the presence of $SO_4$ or $ClO_4$ anions of the same ionic strength, indicating the presence of uncharged and negatively charged complexes of heavy metal with Cl ligands.