• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.3-14
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• 2012

This paper describes experimental results on the seismic performance of SHCC (strain-hardening cement composite) infill wall for improving damage tolerance capacity of non-ductile frame. To investigate the effect of tensile strain capacity and cracking behavior of SHCC materials on the shear behavior of SHCC infill wall, three infill walls were fabricated and tested under cyclic loading. The test parameter in this study is a type of cement composites; concrete and SHCCs. The two types of SHCC materials were prepared for infill walls. In order to induce crack damages into the mid-span of the infill wall, each infill wall had two 100-mm-deep-notches on both sides. Test results indicated that SHCC infill walls showed superior crack control capacities and much larger drift ratios at the peak loads than RC (reinforced concrete) infill wall, as expected. In particular, due to the bridging actions of the reinforcing fibers, SHCC matrix used in this study would delay the stiffness degradation of infill wall after the first inclined cracking. Moreover, from the damage classes based on the cracks' maximum width in the infill walls, it was observed that PIW-SHD specimen possessed nearly threefold seismic capacities compared to PIW-SLD specimen. Also, from the results on the strain of diagonal reinforcements, it can be concluded that the SHCC matrix would resist a part of tensile stresses transferred along steel rebar in the infill wall.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.307-315
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• 2023

In this study, mortar test specimens were produced by varying the mixing ratio of CO₂ reaction hardening cement (CSC) and general cement (OPC), and the mechanical and carbonation characteristics were evaluated by controlling the primary curing temperature and secondary curing CO₂ pressure. Under all curing conditions, it was observed that the higher the CSC ratio in the binder, the lower the mechanical properties. Specifically, a first curing temperature of 60 ℃ yielded higher mechanical properties compared to the case of 20 ℃, and a greater carbonation penetration depth was also observed. At a first curing temperature of 60 ℃, it was noted that the curing pressure and bending strength during the second CO₂ curing were inversely proportional, while the compressive strength showed a proportional relationship. This phenomenon is believed to be due to excessive carbonation, which reduces mechanical properties, and the fact that flexural strength is more sensitive to these properties compared to compressive strength. However, based on the evaluation of the limited curing conditions, it is evident that future test conditions need to be expanded and reviewed more thoroughly.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.32-32
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• 2000

잠입노즐은 로케트 추진기관의 길이 및 중량을 감소시켜 체계설계의 관점에서 볼 때 많은 이점을 제공한다. 본 연구에서는 3단형 과학로케트 원지점 차넣기 모타(apogee kick motor)에 적용하기위한 잠입노즐의 기초기술 개발에 주안점을 두었다. 고고도에서 저속으로 회전하며 비행하는 원지점 차넣기 모타를 제작하기위해서 체계 요구성능에 의해 예상된 실물형의 50% 크기에 해당하는 축소형 잠입노즐을 제작하였다. 잠입노즐은 잠입부의 내외부가 고온의 추진제 연소가스에 노출된 상태에서 노즐 내부 압력 외에 연소실압에 의한 외부압력이 작용하므로 이를 고려한 열 및 구조설계가 중요하다. 본 연구에서는 노즐 수렴부와 목부에 일체형 그라파이트 소재를 적용하고 확장부 내열재 및 잠입부 배면내열재에 탄소/페놀 복합재를 노즐 내열재로 사용하였다. 그리고 이들의 구조적 지지를 위해 스틸구조물을 적용하였다. 적용된 스틸구조물에는 K형 열전쌍을 이용해 내열재와 구조물 온도를 측정할 수 있는 관통구멍 및 나사부를 구조물 외변에 가공하였다. 열전쌍은 노즐 목직경의 2, 4배 되는 확장부 내열재 단면위치의 2mm와 4mm 깊이와 구조물 내면 및 외면의 4개소에 열전쌍을 부착하여 지상연소시험시 노즐 내열재와 구조물의 온도분포를 관찰한다. 그리고 노즐 조립시 확장부 내열재와 구조물에 각 각 반원형 홈을 내어 여분의 접착제가 원형 홈에 밀려들어가 경화되어 노즐 기밀유지와 체결력을 향상시킬 수 있는 원형공간 접착제 충전 공법을 적용하여 실제모타에 대한 적용가능성을 지상연소시험을 통해 확인한다.

• Asian Journal of Turfgrass Science
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• v.5 no.1
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• pp.33-39
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• 1991

This experiment was carried out in order to study the changes of morphological characters of growth and thatch accumulation in perennial ryegrass as affected by the different levels of soil compaction and coring depth. Soil compactions were treated with 10, 20, 30 and 40kg power roller and artificial core depth were 2.5, 5.0, 7.5 and 10.0cm under the ground, respectively. And, artificial core space were fixed 84.5% in all soil compaction levels. The results obtained were summarized as follows: 1. Relationship between number of tillers and root weight was positive significant difference for soil compaction levels. 2. Relationships between shoot dry weight and thatch weight, and number of tillers were positively significant difference for artificial core depths. It may indicate that thatch accumulation depend on the growth of shoot, and increase of shoot dry weight as growth progressed may due to increase of number of tillers, respectively. 3. Soil compaction level of 20kg was greatly influenced on the growth of shoot in all artificial soil depths. Thus, shoot dry weight and number of tillers were obtained the highest value, but thatch and root weight were obtained the lowest values at the soil compaction level of 20kg. It was suggested that soil compaction of 20kg is very suitable rolling factor for turf maintenance. 4. Thatch weight was positively significant difference for the interaction of soil compaction levelXcoring depth.5. Thatch weight was positive significant correlated with root weight, and negative significant correlated with number of tillers by increase of soil compaction levels.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.1
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• pp.34-41
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• 1993

SUS304 is wellknown as difficult-to-machine materials. It is easy to appear workhardened, and workhardening is one of the causes of groove wear on the tool. In this paper, the author would like to compare the width of flank wear with that of groove wear, and to find whether the groove wear can be used as a criterion of a tool life. The design of the twelve tests provides three levels for each variable (speed: 200m/min, 118m/min, 70m/min; feed: 0.3mm/rev, 0.17mm/rev, 0.1mm/rev; depth of cut: 0.4mm, 0.28mm, 0.2mm). The study of tool-life testing by statistical technique follows usual most scientific sequence. So the tool-life predicting equation is calculated by the method of least squares. The overall adequacy of the model can be verified by the analysis of variance. The results obtained are as follows : 1) When SUS304 is cut in 200(m/min), the width of flank wear is much larger than that of groove wear. 2) In cutting speed 118m/min, flank wear is a little larger than groove wear and in the cutting speed 70m/min, the latter is a little larger so that it is reasonable to determine the tool life according the crierion by groove wear in the low cutting speed (less than 70m/min). 3) Owing to the burr the depth of engagement along the cutting edge is extended toward the shank.

• Polymer(Korea)
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• v.30 no.2
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• pp.135-139
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• 2006

To evaluate the dental restorative application of polymer composites filled with hydroxyapatite (HAP) which is an inorganic component of human bone material, dental properties of the polymer composites were investigated. A visible light system was utilized to activate the acrylate resin matrix of the composites. Maximum loading percentage of HAP in composite was 65 wt% and the depth of cure was 6.0 mm which can be applicable for dental restoration. With increasing the HAP content, degree of conversion of polymer composites was slightly decreased, however, polymerization shrinkage value was not varied. Diametral tensile strength value was enhanced with an increase of HAP content, however, there was no strict trend between flexural strength and HAP concentration. Anyhow, polymer composites prepared herein have superior mechanical properties sufficient specifications applicable to dental materials.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.4_2
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• pp.571-576
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• 2023

In this study, the harmless crack size(a_hml) according to the residual stress depth was evaluated using the fatigue limit of SCM440 steel by quenching-tempering(QT) and induction hardening(IH), and threshold stress intensity factor of QT steel. Because the residual stress increased rapidly as the crack depth increased, a_hml was determined at the depth of all the crack aspect ratio(As) regardless of Type I-III, and a_hml also increased according to the residual stress depth. a_hml was minimal at As=1.0 and maximal at As=0.1, but was almost similar on each Type. a_hml was small the dependence on As.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.47-56
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• 2006

The repeated loading responses of four shear-critical reinforced concrete beams with two different shear span-to-depth ratios, were studied. One series of beams was reinforced using pairs of bundled stirrups with $90^{\circ}$ standard hooks, haying free end extensions of $6d_b$. The companion beams contained shear reinforcement made with larger diameter headed bars anchored with 50mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that beams containing headed bar stirrups have a superior performance to companion beams containing bundled standard stirrups with improved ductility, larger energy absorption and enhanced post-peak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.99-109
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• 2009

Fine-size exposed aggregate portland cement concrete pavements (FEACP) have surface texture of exposed aggregate by removing upper 2$\sim$3mm mortar of surface of which curing is delayed by using delay-setting agent. FEACPs have advantages of maintaining low-noise and adequate skid-resistance level during the performance period than general portland cement concrete pavements. It is necessary to ensure the durability environmental loading to prevent unexpected distress during the service life of FEACP. In the process of curing, volume change accompanied change in by moisture and temperature could be an important cause of crack in concrete to construct for successful FEACP, The use of chloride containing deicer may accelerate defects of concrete pavement, such as crack and scaling. This study aim to evaluate environmental loading resistance of FEACP, based on the estimation of shrinkage-crack-control-capability by moisture evaporation and scaling by deicer in freeze-thaw reaction.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.1-15
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• 2009

Surface of exposed aggregate concrete pavements is consists of exposed coarse aggregate by removing upper 2$\sim$3mm mortar of concrete slab. Exposed aggregate concrete pavements have advantages of maintaining low-noise and adequate skid-resistance level during the performance period. In order to provide the successful exposed concrete aggregate pavement, uniform distribution of the coarse aggregate on pavement surface through adequate the mix design and exposing method. The mix design in concrete pavement is generally designed on the basis of strength, but mix design of exposed aggregate pavement employed in this study includes the consideration of noise and skid resistance, as well as strength. Smaller of maximum coarse aggregate is known to be effective for reduce noise level. Optimum mix design and exposing method of fine-size exposed aggregate portland cement concrete pavement that can reducing the noise and maintain the adequate level of skid resistance are proposed in this study. To consider the variation of optimum exposing time due to the hardening speed of mortar by climatic condition, quantitative is also suggested measurement of hardening state.