• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.79-83
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• 2000

Interfacial and microfailure properties of carbon liber/bismaleimide (BMI) composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Since BMI is rather difficult matrix to apply for the conventional fragmentation test because of its too low elongation and too brittle and high modulus properties, dual matrix composite system was applied. After carbon fiber/BMI composite was prepared for rod shape by controlling differing curing stage, composites rod was embedded in toughened epoxy as outer matrix. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile testing, whereas the diagonal slippage in fiber ends was observed during compressive test. On the other hand, AE amplitudes of BMI matrix fracture were higher than carbon fiber tincture under tensile test because BMI matrix has very brittle and high modulus. The waveform of signals coming from BMI matrix fractures was consistent with AE amplitude result under tensile tests.

• Magazine of korean Tunnelling and Underground Space Association
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• v.1 no.1
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• pp.81-87
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• 1999

Effects of blasting vibrations on curing concrete have not been well studied. As a result, unrealistic and costly blasting vibration constraints have been placed on blasting when it occurs in the vicinity of curing concrete. To study the effects of blasting, concrete blocks of $30\times20\times20cm$ were molded and placed on the quarry Different sets of concrete blocks were subjected to peak vibrations of 0.25, 0.5, 1.0, 5.0, and 10cm/sec. The impulses of blasting vibrations were applied at thirty minutes intervals . Along with unvibrated concrete blocks, the vibrated concrete samples with 60.3mm in diameters were measured for elastic moduli, sonic velocity and uniaxial compressive strength. Test results can be summarized as follows : 1) The blasting vibrations between 6 and 8 hours after pour generally have exerted bad influences on the uniaxial compressive strength of the concrete 2) Under low vibration of 0.25cm/sec variations of the uniaxial compressive strength were not shown. As the magnitudes of blasting vibration increased, compressive strength of concrete decreased. But under the vibrations between 5 and 10cm/sec decreases in strength were almost same. 3) Physical properties of the p-wave velocity, Young's modulus, and Poisson's ratio appeared to decrease for the concrete blocks subjected to vibration for 6 to 8 hours.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.3
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• pp.57-63
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• 2004

This study was performed to evaluate the engineering properties of cement mortar brick with loess and fly ash. The unit weight was in the range of $2,068{\sim}2,137\;kgf/m^{3}$ and $1,899{\sim}2,045\;kgf/m^{3}$ in water and dry curing, respectively It was decreased with increasing the loess content. The absorption ratio was in the range of $5.2{\sim}13.1%$ and $8.5{\sim}13.2%$ in water and dry curing, respectively. The compressive strength was decreased with increasing the loess content. The compressive strength of the 193 $kgf/m^{2}$ in water and 188 $kgf/m^{2}$ in dry curing at the curing age 28 days of the binder volume ratio 35% was exceeded in 163 $kgf/m^{2}$ of standard compressive strength about cement bricks. The carbonation depth was in the range of $0.9{\sim}1.4$ mm, $1.2{\sim}3.6$ mm, $1.4{\sim}6.7$ mm and $2.4{\sim}12.5$ mm in dry curing of curing age 14days, 28days, 90days and 360days, respectively.

• Advances in materials Research
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• v.8 no.2
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• pp.103-115
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• 2019

Polypropylene (PP) fibers for making fabric which is used for packing cement have a high strength and high tear resistance. Due to these excellent properties the present study investigates the effect of PP fibers on the mechanical strength of concrete. Mechanical strength parameters such as compressive strength, splitting tensile strength and flexural strength are evaluated. Structural integrity of concrete using Ultrasonic Pulse Velocity (UPV) was also studied. Concrete containing PP fibers in percentage of 0%, 0.15%, 0.25%, 0.5% and 0.75% was developed with a characteristic compressive strength of 25 MPa. Concrete cubes, cylinder and prismatic specimens were cast and tested. It was found that the UPV values recorded for all specimens were of the similar order. Test results indicated the used of PP fibers can significantly improve the flexural and splitting tensile strengths of concrete materials whereas it resulted a decreased in compressive strength. The relative increase in split tensile and flexural strength was optimum at a fiber dosage of 0.5% and a mild decreased were observed in 28 days compressive strength. The findings in this paper suggested that PP fibers deriving from these waste cement bags are a feasible fiber option for fiber-reinforced concrete productions.

• Journal of Powder Materials
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• v.28 no.1
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• pp.13-19
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• 2021

Bulk graphite is manufactured using graphite scrap as the filler and phenolic resin as the binder. Graphite scrap, which is the by-product of processing the final graphite product, is pulverized and sieved by particle size. The relationship between the density and porosity is analyzed by measuring the mechanical properties of bulk graphite. The filler materials are sieved into mean particle sizes of 10.62, 23.38, 54.09, 84.29, and 126.64 ㎛. The bulk graphite density using the filler powder with a particle size of 54.09 ㎛ is 1.38 g/㎤, which is the highest value in this study. The compressive strength tends to increase as the bulk graphite density increases. The highest compressive strength of 43.14 MPa is achieved with the 54.09 ㎛ powder. The highest flexural strength of 23.08 MPa is achieved using the 10.62 ㎛ powder, having the smallest average particle size. The compressive strength is affected by the density of bulk graphite, and the flexural strength is affected by the filler particle size of bulk graphite.

• Tribology and Lubricants
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• v.37 no.2
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• pp.54-61
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• 2021

The effect of the sand blasting before TiAlN coating in the manufacture of WC hard metal alloy tips have been studied. For four different tips, according to the status of processing of the sand blasting and the coating, residual stress measurement by X-ray diffraction and several tests for mechanical properties have been conducted. The results suggest that there was no difference in static mechanical properties, such as hardness, surface roughness and elastic modulus, between two coatings. Furthermore, compressive residual stress was generated equally on their surfaces. Additionally, the compressive residual stress in substrate WC was found to increase greatly when subjected to sand blasting treatment. However, the compressive residual stress decrease after coating regardless of sand blasting treatment. Nevertheless, it is confirmed that the compressive residual stress generated in the coating after sand blasting is less than that in the non-sandblasting coating. This was attributed to the plastic deformation occurring in the WC substrate during coating after sand blasting. In contrast to the scratch test results, sand blasting was assumed to have a negative effect on the adhesion between the coating and substrate. This is because there is a high possibility of microcracks due to plastic deformation in the WC substrate under the coating after sand blasting.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.98-99
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• 2020

This study is aim to assess mechanical properties which is highly related to structural safe and durability of 100MPa high strength concrete mixed with amorphous metallic fiber. All specimens were heated with low velocity heating rate(1℃/min.), residual compressive strength and residual flexural strength was evaluated. The specimens were cooled down to room temperature after heating. As a result, in the case of 100MPa high-strength concrete, the residual compressive strength enhancing effect of amorphous metallic fiber has showed with the mix proportion of fiber. In addition, residual flexural strength showed more regular pattern before 300℃ then residual compressive strength, but simillar decreasing behavior was shown after 300℃ like residual compressive strength. Further study about fiber pull-out behavior and fiber mechanical, chemical property change due to temperature is needed.

• Journal of the Korean Physical Society
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• v.81
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• pp.133-138
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• 2022

Using the first principles calculations, we investigated the strain dependent magnetic properties of the 1T-VSe₂ monolayer (up to ± 3%). We obtained a metallic band structure, and this feature was preserved under both compressive and tensile strain. The pristine system had a magnetic moment of 0.9 µ_B/unit cell and decreased to 0.68 µ_B/unit cell under - 3% compressive strain whereas it was increased to 1.03 µ_B/unit cell under + 3% tensile strain. The 1T-VSe₂ monolayer had an in-plane magnetic anisotropy with a value of - 0.48 meV/cell. The in-plane anisotropy features were maintained in both compressive and tensile strains. The orbital resolved magnetic anisotropy indicated that the V atom contributed to the perpendicular magnetic anisotropy while the Se atom had an in-plane anisotropy. We found that the Se dominated the anisotropy. We also calculated the temperature dependent Curie temperature (T_C). The pristine structure had a T_C of 260 K, and the strain effect enhanced the T_C. Particularly, the compressive strain affected further the exchange parameter resulting in substantial enhancement of the Curie temperature where a T_C of 570 K was achieved at - 3% strain. Our finding regarding the strained VSe₂ could help for further investigation in spintronics and straintronics applications.

• Advances in concrete construction
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• v.14 no.1
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• pp.15-34
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• 2022

The use of waste rubber in concrete can reduce natural aggregate consumption and improve some technical properties of concrete. Although there are several equations for estimating the mechanical properties of concrete containing waste rubber, limited numbers of machine learning-based models have been proposed to predict the mechanical properties of rubbercrete. In this study, an extensive database of the mechanical properties of rubbercrete was gathered from a comprehensive survey of the literature. To model the mechanical properties of rubbercrete, M5P tree and linear gene expression programming (LGEP) methods as two machine learning techniques were employed to achieve reliable mathematical equations. Two procedures of input variable selection were considered in this study. The crucial component ratios of rubbercrete and concrete age were assumed as the input variables in the first procedure. In contrast, the volumes of the coarse and fine waste rubber and the compressive strength of concrete without waste rubber were considered the second procedure of the input variables. The results show that the models obtained by LGEP are more accurate than those achieved by the M5P model tree and existing traditional equations. Besides, the volumes of the coarse and fine waste rubber and the compressive strength of concrete without waste rubber are better predictors of the mechanical properties of rubbercrete compared to the first procedure of input variable selection.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.249-256
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• 2001

The purpose of this study was to remove the excessive air foaming which was produced in mixing the RSLMC(latex-modified concrete with rapid-setting cement) by choosing the best antifoam agent type. A series of RSLMM(latex-modified mortar with rapid-setting cement) experiments were carried out as a basic experiments for RSLMC with the main experimental variables such as antifiamer types(A, B, C, D), antifoamer contents(0, 1, 2, 3%), and latex contents(10, 15%). Air content test and compressive strength tests were carried out to measure the improved properties of RSLMM. SEM analysis, also, was carried to observe the formation of latex film. The results of RSLMM showed that the decrease of 50% air content was obtained by admixturing an antifoam agent by 1%. This made the strength enhanced and the workability be within the purposed. The best properties of compressive strengths was obtained at latex content of 15% and D antifoam agent of 1%. compressive strength increased about 32.6%. The analysis of SEM results no difference in a formation of later film.