• Composites Research
• /
• v.19 no.6
• /
• pp.16-22
• /
• 2006

The puncture properties under various conditions were investigated for the optimum conditions to yield the best properties. Fiber aspect ratio(AR: length of fiber/diameter of fiber), interphase condition and fiber content were considered as variables which impact the puncture force and friction force. The puncture force of short-fiber reinforced rubber increases up to 3.4 times compared to the virgin material. The better interphase condition shows the higher puncture force at given fiber AR and fiber content. The friction force of the matrix and reinforced rubber with a fiber AR below 155 does not exist. The friction force of the reinforced rubber with the good interphase condition and high fiber AR is higher than puncture force of matrix. Overall, it was found that the interphase condition, fiber AR and fiber content have an important effect on the puncture properties.

• Composites Research
• /
• v.20 no.6
• /
• pp.28-33
• /
• 2007

The puncture properties of short-fiber reinforced rubber were investigated as functions of fiber aspect ratio(AR: length of fiber/diameter of fiber), fiber content, specimen size and testing velocity. The puncture stresses of the matrix and short-fiber reinforced rubber decreased with specimen size, and increased with testing velocity at same specimen size. As the fiber AR increased the puncture stress at given fiber content also increased. The problem of the specimen shape was investigated by the comparison of the tensile strength with puncture stress. The forces acting in the membrane wall of the matrix and the short-fiber reinforced rubber showed a similar data regardless of specimen size. And those increased with testing velocity at same specimen size. As the fiber AR increased the force acting in the wall at given fiber content also increased. Overall, it was found that the specimen size, testing velocity had an important effects on the puncture properties.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.8
• /
• pp.27-33
• /
• 2016

In this study, Polyvinyl alcohol (PVA) fiber was used to increase strength (unconfined compressive strength and tensile strength) of bio-cemented sand using microorganism. Ottawa sand was mixed with PVA fibers having three fiber contents (0, 0.4, and 0.8%). The fiber mixed sand was treated 14 times by using Microbially Induced Calcite Precipitation (MICP) which included culture (2 times per day) during 7 days to improve its engineering properties. The Bacillus Sporosarcina pasteurrii (Bacillus sp.) was used for urease activity. The specimen was prepared as a cylindrical specimen of 5 cm in diameter and 10 cm in height. Unconfined compressive strength and tensile strength were measured after cementation. Moreover, calcium carbonate content and SEM analyses were performed with a piece of sample. An average value of unconfined compressive strength increased and then slightly decreased but an average value of tensile strength ratio increased with increasing carbonate content the in same condition. Unconfined compressive strength and tensile strength increased about 30% and 160%, respectively. A strength ratio of unconfined compressive strength to tensile strength representing the brittleness decreased from 8 to 4 when fiber content increased from 0.0 to 0.8%. Such bio-cemented sand can be applied into slope area to prevent its shear failure or increase its tensile strength.

• Journal of the Korea Concrete Institute
• /
• v.24 no.1
• /
• pp.79-86
• /
• 2012

Though steel reinforcing bars are the most widely used tensile reinforcement, corrosion problems are encountered due to the exposure to aggressive environments. As an alternative material to steel, the fiber reinforced polymers have been used as reinforcement in concrete structures. However, bond strength of FRP rebar is relatively low compared to steel rebar. It has been reported that fibers in matrix can resist crack growth, propagation and finally result in an increase of toughness. In this study, high-strength concrete reinforced with structural fibers was produced to enhance interfacial bond behavior between FRP rebar and concrete matrix. The interfacial bond-behaviors were investigated from a direct pullout test. The test variables were surface conditions of GFRP bars and fiber types. Total of 54 pullout specimens with three different types of bars were cast for bond strength tests. The bond strength-slip responses and resistance of the bond failure were evaluated. The test results showed that the bond strength and toughness increased according to the increased fiber volume.

• Korean Chemical Engineering Research
• /
• v.45 no.3
• /
• pp.269-276
• /
• 2007

$TiO_2$-containing pitch fibers were prepared and various stabilization variables were investigated by characterizations of the fibers and behaviors of $TiO_2$ particles in the optimum stabilization conditions. When pitch fiber was stabilized by air at the optimum condition, the fiber weight increased as an increase of the stabilization temperature and a decrease of $TiO_2$ concentration. The carbonization yield was 71~82 wt.%, showing a decrease of the yield with the $TiO_2$ increase caused by the catalytic activity of $TiO_2$ to combustion. During the stabilization, newly developed carbonyl and carboxyl groups were introduced on the fiber surface and cross-linking reactions were progressed resulting the thermosetting property, which was verified by the replacement of hydrogen with oxygen. Pore size of the activated carbon fiber was increased by an increase in $TiO_2$ concentration. In the considerations of the aggregation behaviors of the $TiO_2$ particles, the optimum stabilization conditions of 0.5 wt.% $TiO_2$ containing petroleum-based pitch fiber were suggested as $280^{\circ}C$, 3 hr.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.2
• /
• pp.155-163
• /
• 2007

High Strength Concrete (HSC) has weakness that in a fire, it is spalled and brittles. The phenomenon of spalling is made by water vapor's (resulting from evaporation in the material at over $100{^{\circ}C}$)' being confined in watertight concrete. As the concrete strength increases, the degree of damage caused by the spalling becomes more serious because of the permeability. It is reported that the polypropylene(PP) fiber has an important role in protecting concrete from spalling and the optimum dosage of PP fiber is 0.2%. This study was conducted on the nonreinforced concrete specimens. The high-temperature behavior of high-strength reinforced concrete columns with various concrete strength and various dosage of PP fibers was investigated in this study. The results show that the ratio of unstressed residual strength of columns increases as the concrete strength increases and the ratio of unstressed residual strength of columns increases as the dosage of PP fiber increases from 0% to 0.2%, however, the effect of fiber dosage on residual strength of column barely changes above 0.2%.

• Composites Research
• /
• v.13 no.5
• /
• pp.10-17
• /
• 2000

The fatigue properties of short nylon66 fiber reinforced Chloroprene rubber have been investigated as functions of interphase conditions and fiber content. The spring constant of rubber decreased about 21% after the fatigue test. On the contrary, that of reinforced rubber increased in all cases. The changing rate of spring constant for reinforced rubber decreased with increasing fiber content. This means that the better interphase condition, the smaller changing rate of spring constant. Temperature of matrix increased about 2.5 times and one of reinforced rubber showed 1.7∼2 times up after the test. The changing rate of temperature for reinforced rubber during fatigue test decreased with increasing fiber content. It is found that the better interphase condition, the smaller changing rate of specimen temperature at the same fiber content. Double coatings of bonding agent 402 and rubber solution became the best interphase model in this study. And, we have investigated the possibility of applying short-fiber reinforced rubber to automotive engine mount rubber, bush and stopper.

• Composites Research
• /
• v.13 no.3
• /
• pp.30-37
• /
• 2000

The dynamic properties of short-fiber reinforced Chloroprene rubber have been studied as functions of interphase conditions and fiber content. The loss factor generally decreased with fiber content and showed different patterns according to interphase conditions. The better interphase condition showed the lower loss modulus, $E_2$. Also, the dynamic ratio decreased with fiber content and rapidly decreased in the case of double coatings, i.e., model C. Therefore, the short-fiber reinforced rubber could have the better isolation in frequency ratio($\sqrt{2}$ min.) compared to frequency ratio($\sqrt{2}$ max.). And we have investigate the possibility of applying short-fiber reinforced rubber to automotive engine mount.

• Tunnel and Underground Space
• /
• v.31 no.6
• /
• pp.469-479
• /
• 2021

As a material for preventing spalling of concrete, the effectiveness of PP fiber has already been confirmed. However, it is necessary to consider the maximum temperature that occurs during a fire, and to solve the mixing problem and the strength reduction problem that occur depending on the mixing amount. In this study, the fire resistance performance of tunnel segment linings according to the PP fiber content and air volume under the RABT fire scenario was investigated. As a result, no spalling or cross-sectional loss occurred in all test specimens, and when the PP fiber content was small, the maximum temperature was relatively high and the maximum temperature arrival time was also fast. On the other hand, no trend was found for the maximum temperature and arrival time according to the difference in air volume. In the internal temperature distribution results for the PP fiber mixing amount of 0.75, 1.0, 1.5, and 2.0 kg/m³, the results of 0.75 and 1.0 kg/m³ showed similar temperature distribution, and the results of 1.5 and 2.0 kg/m³ were similar. It was confirmed that the internal temperature distribution tends to decrease at the same depth when the amount of PP fiber mixed is large, and it was confirmed that a remarkable difference occurred from the results of 1.0 kg/m³ and 1.5 kg/m³ of PP fiber mixed amounts.

• Composites Research
• /
• v.20 no.5
• /
• pp.13-19
• /
• 2007

Fiber-reinforced thermoplastic composites not only approach almost near to the strength of thermosetting composite but also has excellent productivity, recycling property, and impact resistance, which are pointed as weaknesses of thermosetting composites. The study for strength calculation of one direction fiber-reinforced thermoplastic composites and the study measuring precisely fiber orientation distribution were presented. Need the systematic study for the data base that can predict mechanical properties of composite material and fiber orientation distribution by the fiber content ratio was not constructed. Therefore, this study was investigated what affect the fiber content ratio and fiber orientation distribution have on the strength of composites. Fiber-reinforced thermoplastic composites by changing fiber orientation distribution and the fiber content ratio were made. Tensile strength ratio of $0^{\circ}$ direction of fiber-reinforced composites increased being proportional the fiber content and fiber orientation function as change from isotropy(J=0) to anisotropy(J=1). But, tensile strength ratio of $90^{\circ}$ direction by separation of fiber filament decreased when tensile load is imposed fur width direction of reinforcement fiber length direction.