• Advances in concrete construction
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• 제3권4호
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• pp.269-282
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• 2015

In this paper, a compression to tensile load converter device was developed to determine the anisotropic tensile strength of concrete. The samples were made from a mixture of water, fine sand and cement, respectively. Concrete samples with a hole at its center was prepared and subjected to tensile loading using the compression to tensile load converter device. A hydraulic load cell applied compressive loading to converter device with a constant pressure of 0.02 MPa per second. Compressive loading was converted to tensile stress on the sample because of the overall test design. The samples have three different configurations related to loading axis; 0, $45^{\circ}$, $-45^{\circ}$. A series of finite element analysis were done to analyze the effect of hole diameter on stress concentration of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, Brazilian test and three point loading test were also performed to compare the results from the three methods. Results obtained by this device were quite encouraging and show that the tensile strengths of concrete were similar in different directions because of the homogeneity of bonding between the concrete materials. Also, the indirect tensile strength was clearly lower than the Brazilian test strength and three point loading test.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.939-952
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• 2016

A compression to tensile load transforming (CTT) device was developed to determine indirect tensile strength of concrete material. Before CTT test, Particle flow code was used for the determination of the standard dimension of physical samples. Four numerical models with different dimensions were made and were subjected to tensile loading. The geometry of the model with ideal failure pattern was selected for physical sample preparation. A concrete slab with dimensions of $15{\times}19{\times}6cm$ and a hole at its center was prepared and subjected to tensile loading using this special loading device. The ratio of hole diameter to sample width was 0.5. The samples were made from a mixture of water, fine sand and cement with a ratio of 1-0.5-1, respectively. A 30-ton hydraulic jack with a load cell applied compressive loading to CTT with the compressive pressure rate of 0.02 MPa per second. The compressive loading was converted to tensile stress on the sample because of the overall test design. A numerical modeling was also done to analyze the effect of the hole diameter on stress concentrations of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, the Brazilian test was performed to compare the results from two methods and also to perform numerical calibration. The numerical modeling shows that the models have tensile failure in the sides of the hole along the horizontal axis before any failure under shear loading. Also the stress concentration at the edge of the hole was 1.4 times more than the applied stress registered by the machine. Experimental Results showed that, the indirect tensile strength was clearly lower than the Brazilian test strength.

• 대한건축학회논문집:구조계
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• 제35권8호
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• pp.131-138
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• 2019

Since concrete has a low tensile strength compared to the compressive strength, reinforced concrete flexural members represent easy crack occurance under a small load. In order to overcome this problem, steel fiber reinforced concrete has been developed to compensate the tensile strength and brittleness of members. However, in the design formula of the domestic building code, it is not specified in the design formula reflecting the material characteristics. Therefore, the field application of the steel fiber reinforced concrete have had many restrictions. In this study, a flexural tensile strength model of steel fiber reinforced concrete is proposed by collecting and analyzing the material properties of material test results conducted by various researchers, and verified by the test results of cracking and stiffness evaluation of flexural members based on the proposed model. As a result of this study, the flexural tensile strength model of steel fiber reinforced concrete which can reflect the mixing ratio and aspect ratio of the steel fiber was proposed and the validity of the proposed material model equation was evaluated from the load-deflection relationship in the flexural test of the slab member.

• Carbon letters
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• 제6권4호
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• pp.234-242
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• 2005

Bending and tensile properties of 2D cross-ply C/C composites with processing heat treatment temperature (HTT) are evaluated. C/C composites used are made from two types of PAN based T700 and M40 carbon fibers with phenolic resin as carbon matrix precursor. Both the types of composites are heat treated at different temperatures (ranging from 750 to $2800^{\circ}C$) and characterized for bending and tensile properties. It is observed that, real density and open porosity increases with HTT, however, bulk density does show remarkable change. The real density and open porosity are higher in case T-700 carbon fiber composites at $2800^{\circ}C$, even though the density of M40 carbon fiber is higher. Bending strength is considerably greater than tensile strength through out the processing HTT due to the different mode of fracture. The bending and tensile strength decreases in both composites on $1000^{\circ}C$ which attributed to decrease in bulk density, thereafter with increase in HTT, bending and tensile strength increases. The maximum strength is in T700 fiber based composites at HTT $1500^{\circ}C$ and in M40 fiber based composites at HTT $2500^{\circ}C$. After attending the maximum value of strength in both types of composite at deflection HTT, after that strength decreases continuously. Decrease in strength is due to the degradation of fiber properties and in-situ fiber damages in the composite. The maximum carbon fiber strength realization in C/C composites is possible at a temperature that is same of fiber HTT. It has been found first time that the bending strength more or less 1.55 times higher in T700 fiber composites and in M40 fiber composites bending strength is 1.2 times higher than that of tensile strength of C/C composites.

• 한국지반공학회논문집
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• 제24권6호
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• pp.37-44
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• 2008

낮은 응력 상태에서 모래의 인장강도는 포화도 또는 흡입력에 따라 증가하다 최대값이 이른 후 감소한다. 최대인장 강도는 어느 포화도에서든 발생될 수 있다. 선행 연구에서는 이와 같은 습윤 모래의 인장강도를 정확히 표현한 이론이 제시되었다. 본 연구에서 세 가지 종류의 모래(워싱턴 주 시애틀의 검정 Esperance모래, 오스트리일리아 서부 Perth 해변 모래, Ottawa 모래)에 대해 실시된 일축인장실험, 함수특성실험, 직접전단실험 결과를 이용하여 제안된 이론을 검증하였다. 제안된 닫힌 형식의 식으로 표현된 이론은 이들 모래들로부터 얻어진 실험결과와 비교 시 전체 포화도 영역에서 인장강도 변화양상, 인장강도 크기, 최대인장강도, 최대인장강도가 발생할 때의 해당 포화도 등을 잘 예측하는 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.359-362
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• 2003

Carbon fiber sheet is attractive due to its good tensile strength, resistance to corrosion, and low weight. The strengthening of concrete structures with externally bonded carbon fiber sheets is increasingly being used for repair and rehabilitation of existing structures. However CFS strengthened beams break down under the service loads. As rupture strain is not reached ultimate value, reduction of the tensile strength is recommended. This study evaluate CFS tensile strength reduction factor which is required to analyze bending moment.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.787-790
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• 2000

This paper presents an experimental study on flexural behavior of structural member enlarged with epoxy mortar system. The main test variable is flexural tensile strength. A series of 4 test beams was tested to shoe the corresponding effect of each variables on maximum load capacity, load-deflection and moment-curvature relationship, interface behavior and failure mode. The results show that the flexural tensile strength of retrofitted materials have no relation load-deflection, but to load-strain, and failure mode.

• Transactions on Electrical and Electronic Materials
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• 제13권5호
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• pp.248-251
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• 2012

In order to develop a high voltage insulation material, epoxy/micro-silica composites (EMC) and epoxy/micro-silica/nano-silica composites (EMNC) with three different particle sizes in ${\mu}m$ and one particle size in nm were prepared and their tensile and flexural tests were carried out and the data was estimated by Weibull statistical analysis. The tensile strength of the neat epoxy was 82.8 MPa and those of the EMCs were larger than that of the neat epoxy, and they were much more advanced by the addition of 10 nm sized nano-silica to the EMCs. Flexural strength showed the same tendency of the tensile strength. As the micro-particle size decreased, tensile and flexural strength increased.

• Journal of the Korean Wood Science and Technology
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• 제26권2호
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• pp.16-23
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• 1998

This paper examines the effects of specimen length and grade on the strength and stiffness properties of structural timber of radiata pine. The tensile strength and modulus of elasticity of 1,902 machine-graded boards with 3.15- and 1.62-m clear span lengths, were determined using a horizontal tension test machine. The mean failure and characteristic stress values for tensile strength show an extremely high dependency on test specimen length. The mean and characteristic values of both modulus of elasticity and tensile strength show significant dependency on machine stress grades.

• Journal of Welding and Joining
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• 제18권6호
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.