• 한국자동차공학회논문집
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• 제10권2호
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• pp.96-100
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• 2002

The purpose of this paper is presented a rational method of predicting dynamic/impact tensile strength of high tensile steel materials widely used fur structural material of automobiles. It is known that the ultimate strength is related with the loading speed and the Lethargy Coefficient from the tensile test. The Dynamic Lethargy Coefficient is proportional to the disorientation of the molecular structure and indicates the magnitude of defects resulting from the probability of breaking the bonds responsible for its strength. The coefficient is obtained from the simple tensile test such as failure time and stresses at fracture. These factors not only affect the static strength but also have a great influence on the dynamic/impact characteristics of the joist and the adjacent structures. This strength is used to analyze the failure life prediction of mechanical system by virtue of its material fracture. The impact tensile test is performed to evaluate the life parameters due to loading speed with the proposed method. Also the evaluation of the dynamic/impact effect on the material tensile strength characteristics is compared with the result of Campbell-Cooper equation to verify the proposed method.

• 한국지반환경공학회 논문집
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• 제11권11호
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• pp.77-85
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• 2010

석탄회를 주재료로 하는 저강도 고유동화재의 특성을 분석하기 위해 일축압축강도시험을 수행하였으며, 경화 시간을 분석하였다. 동일한 배합비 상태에서 함수비가 낮을수록 일축압축강도 증가율이 큰 것으로 나타났으며, 초기 3일 동안에는 이와 같은 현상이 뚜렷하게 나타나고 있음을 확인하였다. 또한, 가장 경제적인 시멘트 첨가비로 소형 모형지반을 조성하여 동적콘관입시험을 통해 배합비에 따른 저강도 고유동화재의 특성을 분석한 결과, 목표 일축압축강도인 500kPa(콘관입률 20mm/blow) 도달시간은 약 10일 정도 소요되는 것으로 나타났으며, 10일이 경과한 후에는 배합비와 상관없이 경화속도가 급격하게 감소하는 것으로 나타났다.

• 한국군사과학기술학회지
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• 제17권4호
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• pp.413-421
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• 2014

Since the structural temperature of a flight vehicle flying at high speed rises rapidly due to aerodynamic heating, it is necessary for optimum structural design to obtain proper material properties at high temperature by taking into account of its operational environment. For a special alloy, analysis data on strength change due to exposure time to high temperature are very limited, and most of them are for an exposure time longer than 30 minutes for long term operations. In this study, base and weld metal samples of Ti-6Al-4V alloy had been prepared and high temperature tensile tests with induction heating were performed, and then high temperature strength characteristics and strength recovery characteristics through cooling have been analyzed. Pre-tests to determine maximum heating rate were performed, and response characteristics for temperature control were confirmed. As a result, high temperature tensile strength appeared to be lower than that of room temperature, but it was higher than that of high temperature of 30 minite exposure listed in MMPDS. In strength recovery through cooling Ti-6Al-4V alloy has shown higher recovery rate compared with other alloys.

• 한국농공학회논문집
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• 제58권1호
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• pp.61-71
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• 2016

This study performed the physical and mechanical experiment on the samples of costal marine clays individually collected in western and southern regions to identify the characteristics of western and southern costal marine clay. Based on the experiment result, the characteristics of costal marine clay is identified undrained shear strength. Based on the experiment result on the physical and mechanical characteristics of costal marine clays, the regression is presented that can analyze the mechanical characteristics of undrained shear strength in costal marine clay of Korea, region of Korea and western-southern region. The correlation of uniaxial compressive strength and undrained shear strength was suitable for use of western-southern region correlation equation. The test result of Jeonnam Yeosu area compares with prediction results of previous researchers formula and western-southern region formula. Prediction results appear highest reliability on the 0.827 of coefficient of determination in the prediction results of the western-southern region formula.

• Structural Engineering and Mechanics
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• 제18권4호
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• pp.493-516
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• 2004

This paper addresses the behavior and strength of structural walls with a concrete compressive strength exceeding 69 MPa. This information also enhances the current database for improvement of design recommendations. The objectives of this investigation are to study the effect of axial-load ratio on seismic behavior of high-strength concrete flexural walls. An analysis has been carried out in order to assess the contribution of deformation components, i.e., flexural, diagonal shear, and sliding shear on total displacement. The results from the analysis are then utilized to evaluate the prevailing inelastic deformation mode in each of wall. Moment-curvature characteristics, ductility and damage index are quantified and discussed in relation with axial stress levels. Experimental results show that axial-load ratio have a significant effect on the flexural strength, failure mode, deformation characteristics and ductility of high-strength concrete structural walls.

• 한국안전학회지
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• 제16권1호
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• pp.53-58
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• 2001

Constructions on the soft clay layer of low strength and high compression bring out many problems. Recent studies show that strength of the soft clay layer could be substantially improved by mixing quicklime. For the purpose, a series of uniaxial compression tests were performed, using quicklime, in order to analyze strength characteristics. The major test results are summarized following : When water content is 90%, the strength is observed to precipitously increase between 3～14 days, then, the extent slowly increase in relative terms. When water content is 130%, the strength is observed to precipitously increase up to 28 days. When the strength of water content 90% is compared to that of water content 130%, the initial strength of the former is higher than that of the latter. The analyses show that the improvement of soft clay layers can be realized by the mixture of both quicklime and sand, and by the mixture of quicklime only.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.489-494
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• 2010

A geo-composite soil (GCS) is a stabilized mixture of bottom ash, cement and dredged soil. Various samples with different mass ratios of mixtures were tested under curing time of 7 and 28 days to investigate physical properties and compressive strength. This paper focused on the effect of bottom ash on the strength characteristics of Busan marine dredged soil. Cement has been added as an additive constituent to enhance self-hardening of the blended mixture. The unconfined compressive strength of GCS increases with an increase in curing time due to pozzolanic reaction of the bottom ash. The strength after 28 days of curing is found to be approximately 1.3 to 2.0 times the strength after 7 days of curing, regardless of mixture conditions. The secant modulus of GCS is in the range of 55 to 134 times the unconfined compressive strength. The correlation of unconfined compressive strength with bottom ash content and initial void ratio are suggested.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.377-384
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• 2000

The characteristics and prediction model of the shear strength for unsaturated residual soils was studied. In order to investigate the influence of the initial water content on the shear strength, unsaturated triaxial tests were carried out varying the initial water content, and the applicability of existing prediction models for the unsaturated shear strength was testified. It was shown that the soil - water characteristic curve and the shear strength of the unsaturated soil varied with the change of the initial water content. A sample compacted in the lower initial water content needs a higher suction to get the same degree of saturation while the shear strength of a sample with the lower initial water content displays a lower value. In order to apply the existing prediction models of the unsaturated shear strength to granite residual soils, a correction coefficient, α, on the internal friction angle, ø'was added.

• 한국농공학회논문집
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• 제50권5호
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• pp.51-60
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• 2008

This study is to relate the bond characteristics of CFRP rebar in high strength concrete incorporated with silica fume(SF) and metakaolin(MK). An direct bond test were performed to evaluate the effect of SF and MK on bond properties of high-strength concrete and CFRP rebar. The high strength concrete mix included four SF and MK mixes with 0%, 5%, 10% and 15%. Results of bond performance experiment in relation to pullout vs slip behavior of FRP rebar and high strength showed better performance of SF than MK. Also, the results showed the improved bond strength as replacement ratio of SF and MK increased. The relative bond strength in which $1.3{\sim}3.2$ of estimated values were obtained.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1990년도 가을 학술발표회 논문집
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• pp.125-130
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• 1990

Fly Ash in concrete is known to be effective in improving workability, the reduction of heat of hydration, increasing the long-term compressive strength, and improving durability. Recently, fly ash is consedered an essential material for the high-strength concrete. In this paper, investigations for the strength and workability characteristics was carried out when fly ash was used in the high-strength concrete. As the result, fly ash was effective in increasing the long-term compressive strength, but the short-term compressive strength was gradually decreased with increating fly ash contents. And also the use of superplasticzers was required for providing the proper workability when fly ash contents were increased. The optimum content of fly ash was about 10%.