• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.29-36
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• 1991

The effects of heat treatment on fatigue crack growth behavior were studied in continuously reinfored, magnesium-based composite (FP/ZE41A). Following an earlier TEM investigation, specimens were thermally aged to modify the interfacial zone between the alumina fibers and mg alloy matrix. The fatigue crack growth experiments were conducted with specimens having the fiber orientation normal to the crack growth direction(longitudinal) and also specimens with the fibers oriented parallel to the crack growth direction(transverse). A comparision of the fatigue crack growth behavior indicates that aged longitudinal specimens are more resistant to fatigue crack growth than as-fabricated longitudinal specimens. Conversely, as-fabricated transverse specimens are more resistant to fatigue crack growth than aged transverse specimens. SEM observations of fiber pullout and ductile tearing on the fatigue fracture surfaces indicate that the aging weakens the strength of the fiber/matrix interface, giving rise to the observed fatigue crack growth behavior.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.413-419
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• 2002

Particulate composites of $Al_2O_3$/TiC/SiC, $Al_2O_3$/TiC and $Al_2O_3$/SiC have been fabricated by hot pressing and their R-curve behaviors and mechanical properties were investigated. $Al_2O_3$ containing 30 vol% TiC particles showed higher toughness by 8% than that for monolithic alumina and its fracture strength was increased significantly by approximately 30%. On the other hand, the addition of 30 vol% SiC of $3{\mu}m$ in $Al_2O_3$ decreased the fracture strength slightly but induced a rising R-curve behavior owing to the strong crack bridging of SiC particles. In case of $Al_2O_3$/TiC/SiC, arising R-curve behavior was also observed and the fracture toughness reached 6.6 MPa${\cdot}\sqrt{m}$ at the crack length of $1000{\mu}m$, which was lower than that of $Al_2O_3$/SiC, however, while the fracture strength was higher by about 20%. The fracture toughness seemed to be decreased as smaller TiC particles roughened the SiC interface and pullout of the SiC particles for crack bridging became less active.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1183-1192
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• 1989

본 논문에서는 평면변형률 상태하에서 안정하게 성장하는 균열선단에 집중 되어있는 강소성역의 해석에 역점을 두어 재결정법과 탄.소성유한요소법을 도입하여 안정 성장균열 선단에 형성되는 균열 성장저항에 직접적인 영향을 미치고 있는 소성 역의 크기나 형태에 대한 실험 및 해석을 하였다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.82-91
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• 2019

In this study, in order to evaluate Hydration Heat Characteristics of mass concrete using ternary blended cement for large underground structures, the analysis considering the temperature history and the thermal characteristics inside the actual structure was performed. The results of the analysis are compared with the measured values to verify the reliability of the analysis and to evaluate the crack resistance performance. As a result of the measured the actual structure temperature, The adiabatic temperature rise coefficients K and ${\alpha}$ of the slab were $35.1^{\circ}C$ and 0.72, respectively, and the wall was analyzed as $29.3^{\circ}C$ and 0.67. The analytical results and the correlation coefficients(r) were 0.95 and 0.98, respectively. As a result of evaluating the crack resistance of slab and wall, the minimum crack index of slab and wall was 1.22 and 1.20, respectively. These results were found to satisfy the site management standards.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.683-692
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• 2020

A joint displacement resistance evaluation method for selecting waterproofing materials in railway bridge decks is proposed. The displacement range for an evaluation is determined by finite element method (FEM) analysis of a load case based on an existing high-speed PSC Girder Box railroad bridge structure. The FEM analysis results were used to calculate the minimum joint displacement range to be applied during testing (approximately 1.5 mm). For the evaluation, four commonly used waterproofing membrane types, cementitious slurry coating (CSC), polyurethane coating system (PCS), self-adhesive asphalt sheet (SAS), and composite asphalt sheet (CAS), were tested, with five specimens of each membrane type. The joint displacement width range conditions, including the minimum displacement range obtained from FEM analysis, were set to be the incrementing interval, from 1.5, 3.0, 4.5, and 6.0 mm. The proposal for the evaluation criteria and the specimen test results demonstrated how the evaluation method is important for the sustainability of high-speed railway bridges.

• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.61-72
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• 2011

In this study, the structural details of steel girder-abutment joints with shear connectors and tie bars were suggested to improve the rigid behavior and crack-resisting capacity of the joints in integral bridges. Experimental loading tests of steel girder-abutment joint specimens with the proposed and empirically constructed structural details were carried out, and the capacities and behavioral characteristics of the joints were evaluated through loading tests. Based on the results of the loading tests, it was estimated that all types of tested joints can be applied to the steel girder-abutment joints because they have sufficient stiffness and crack-resisting capacity under the required design and yield loads. According to the initial stiffness, crack propagations, and load-strain relationships, however, the joints with shear connectors and tie bars showed better structural behaviors compared to the empirically constructed joint.

• International Journal of Highway Engineering
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• v.14 no.2
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• pp.1-10
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• 2012

As old concrete pavements of over 20years in age are increasing in expressways, the repair and rehabilitation of concrete pavement have become an important issue. Although asphalt overlay is widely used as an alternative to rehabilitate the old concrete pavement, problems due to infiltrated water such as reflection crack and pothole are imposing a very serious threat to its performance. This study proposes waterproof membrane as a solution to minimize the damage due to reflection crack and infiltrated water, and accelerated pavement testing was carried out for the performance comparison of composite pavement with waterproof membrane and ordinary tack coating. The experiment used water spraying to simulate rainfall, and the behavior and moisture resistance characteristics of overlay pavement were analyzed. The experimental result indicated that the strain pattern of waterproof membrane section differed from ordinary tack coating section because waterproof membrane caused the asphalt pavement and concrete pavement to move together. Additionally, since waterproof membrane minimized the infiltration of water and delayed the occurrence of reflection crack by about 70% in comparison to ordinary tack coating method. Moreover, the damage due to infiltrated water also decreased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.102-108
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• 2010

The main objective of this study was to evaluate the effect of recycled PET (RPET) fiber made from waste PET bottles to examine application on concrete member. To evaluate the reinforcement effect of RPET fiber in concrete member, experimental tests were performed, such as mechanical property tests (compressive strength, modulus of elasticity and splitting tensile strength) and drying shrinkage test. In mechanical property tests, compressive strength and modulus of elasticity in concrete mixed with RPET fiber gradually decreased, but splitting tensile strength gradually increased as volume fraction of fiber increased. In drying shrinkage test, free drying shrinkage increased. In restrained case, in contrast, crack occurrence was delayed because of tensile resistance increase by RPET fiber. The comparison of RPET and PP fiber added concrete specimen's properties showed that two materials had similar properties. In conclusion, RPET fiber is an alternative material of PP fiber, even finer for its excellence in eco-friendliness due to the recycling of waste PET bottles and its possible contribution to the pollution declination.

• Journal of the Korean Geotechnical Society
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• v.37 no.3
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• pp.5-17
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• 2021

This study aims to investigate the causes and countermeasures for the occurrence of tension cracks in the slope of the rock mass of heavy equipment for road construction. Electric resistivity survey was performed to investigate the expandable tensile crack range. As a result of examining the distribution of soft zones in the rock mass, a low specific resistance zone was found at the bottom of the access road where tensile cracks occurred. It was confirmed that a low resistivity zone was distributed near the top of the excavation slope. Therefore, reinforcements was performed by determining the location of the possible tensile crack as the top of the excavation slope. Two rows of reinforced piles and anchors were proposed as a reinforcement method, and the slope stability analysis showed that the allowable safety factor was satisfied after reinforcements.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.78-85
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• 2023

In this study, synthetic fibers were applied to reduce shrinkage cracks that may occur in mortar produced by 3D printer. We used a biopolymer in powder form made from cactus stem (CS) as an admixture. The material properties of 3D printed mortar were experimentally evaluated. Replacing methylcellulose(MC) with 10% CS increases compressive strength by 9.84-23.92% regardless of the casting method. In addition, regardless of the casting method, shrinkage change, freeze-thaw resistance, and crack resistance are more effective than Plain. Incorporation of CS increases the polysaccharide macromolecular structure and improves durability. Mortars reinforced with synthetic fibers do not affect compressive strength and freeze-thaw. It is also effective for shrink deformation and crack resistance. Incorporating CS and fibers from 3D-printed mortar was found to be effective for durability and crack resistance.