• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.781-789
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• 1988

The fatigue crack growth and crack closure behavior of long through-thickness cracks and small half-penny shaped surface cracks were investigated in 5083-H113 Aluminum alloy under constant amplitude testing by the unloading elastic compliance method. It was found that, in the Region II, the crack growth behavior of both through-thickness and surface cracks exhibited the tri-linear form with two transitions and no concern with stress ratio R. In the Region I $I_{ab}$ and I $I_{b}$, through-thickness cracks grew faster than surface cracks in length direction, but at .DELTA. K .leq.4 MPa.root.m for R=0.1 the growth rates of surface cracks in depth direction, grew faster than those of through-thickness cracks. When the crack closure was considered, the growth rates of through-thickness cracks lay between the growth rates of depth direction and the growth rates of length direction in surface cracks. It is suspected that this was caused by the difference of crack closure at depth and length direction of surface cracks.s.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.535-541
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• 2018

In this study, wedge splitting tests were performed to evaluate fracture behavior of particle reinforced composite materials. Crack resistance was evaluated by using CTOD (crack tip opening displacement) and crack tip opening angle (CTOA). The particle reinforced composites were tested under various temperature ($-60^{\circ}C{\sim}50^{\circ}C$) and load speed (5~500mm/min). Also, digital image correlation method (DIC) was used to analyze the strain field at crack tip. Test results showed that the fracture energy increased with decreasing temperature and crack resistance increased with increasing load velocity.

• International Journal of Highway Engineering
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• v.1 no.1
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• pp.97-106
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• 1999

This study was conducted to develop a test system for evaluating resistance against reflection cracking in shear mode caused by wheel load in asphalt concrete overlaid on the deteriorated cement concrete pavement. Reflection cracking resistance of selected polymer modified asphalt(PMA) mixtures with and without reinforcement was evaluated using this test system. It was shown that the test results accounted for the effectiveness of materials and reinforcement characteristics in terms of the difference in the resistance against reflection cracking. A shear failure life of a certain mixture was estimated with a high coefficient of determination. when the test results were used in a well known prediction model. Therefore, it seemed to be possible to use this technique for predicting a relative service life of on overlay.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.3
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• pp.193-199
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• 2002

Structral crack of RC structure generally occurs when the tension stress by applied load is larger than tension resistance of concrete, and it means deterioration of structure and the decrease of load resistance. Because structural crack of structure can occur critical damage to structure occasionally, the research on crack detection algorithm of RC structure is needed for assurance of structural safety and effective maintenance of structure. In this paper, we executed the laboratory test on measuring strain of RC beam's tension and compression zone, using strain gauge which is widely used on strain measurement of civil structure. By using measured strain, we analyzed strain change, elastic modulus change, and neutral axis change to detect crack of RC beam. As a result, we proposed the simple and effective crack detection algorithm using trends of neutral axis position change.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.173-176
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• 2008

Use of concrete has undoubtedly become widespread in construction. Sensors are used to add functional characteristics to concrete. Self-diagnosing, smart concrete is also being developed. Development of these functional materials and structures will play an important role in protecting buildings and structures against external factors brought about by unusual weather among others. In this study, the innovative measurement system is presented where material damages and internal stress can simply be detected against the compressive and bending force of the structure using light-emitting diode and the resistance property of electric fuse.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.210-215
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• 2019

Concrete members with wide surface area are vulnerable to cracking due to material behavior such as hydration heat and drying shrinkage. Recently many researches have been performed on improvement of strength and cracking resistance through fiber reinforcement, which are mainly focused on enhancement of tensile strength against cracking due to material behavior. In this paper, CFs(Cellulous Fibers) are manufactured for slurry type, and the engineering properties in cement mortar incorporated with CFs are evaluated for flow-ability, compressive, and flexural strength. Through SEM analysis, a pull-off characteristics of CF in matrix are analyzed. With CF addition of $0.5kg/m^3{\sim}1.0kg/m^3$, flexural strength is much improved and enough toughness of pull-off is also observed unlike plastic fiber containing smooth surface.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.29-34
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• 2014

Particulate reinforced composite is composed of hard particles and polymer matrix. This material has been widely applied for engineering industry such as automobile, construction and aerospace. For the safe application, it is important to assess crack resistance behavior. Especially in aerospace industry, crack could cause significant problem when the material is used for solid rocket fuel. Therefore, it is inevitable to estimate the characteristics of the crack propagation. In this study, crack propagation tests were conducted using particulate reinforced composite under crosshead rate 2.54 mm/min in the range of temperature $-60^{\circ}C$ to $60^{\circ}C$. The strain contour of surface for specimen was generated using digital image correlation method.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.600-608
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• 2022

This study investigates the effect of layered double hydroxide (LDH) on the healing performance of self-healing concrete by assessing the chloride penetration resistance of self-healing cement mortars using electrical chloride ion migration-diffusion test. Test results show that both mortars containing healing materials only and mortars containing healing materials and Ca-Al LDH together mostly had higher migration-diffusion coefficients right after cracking, but the migration-diffusion coefficients decreased more than that of OPC with increasing healing ages, and thus, they yielded higher healing capacities than OPC. Also, mortars containing Ca-Al LDH together with healing materials showed higher reduction of their migration-diffusion coefficients, and thus, higher healing capacities than mortars containing healing materials only. This suggests that as the self-healing product increases on the crack surface, the binding of chloride ions by LDH inside the crack increases.

• Journal of Power System Engineering
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• v.15 no.6
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• pp.73-80
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• 2011

The experimental investigation focuses on an influence of artificial aging time in longitudinal butt welded Al 6013-T4 aluminum alloy on the fatigue crack growth resistance. The preferred welding processes for this alloy are frequently tungsten inert gas welding (TIG) process due to its comparatively easier applicability and better weldability than other gas metal arc welding. Fatigue crack growth tests were carried out on compact tension specimens (CT) in longitudinal butt TIG welded after T82 heat treatment was varied in three artificial aging times of 6 hours, 18 hours and 24 hours. Of the three artificial aging times, 24 hours of artificial aging time are offering better resistance against the growing fatigue cracks. The superior fatigue crack growth resistance preferred spatial variation of materials within each specimen in the Paris equation based on reliability theory and fatigue crack growth rate by crack length are found to be the reasons for superior fatigue resistance of 24 hours of artificial aging time was compared to other joints. The highest of crack propagation resistance occurs in artificial aging times of 24 hours due to the increase in grain size (fine grained microstructures).

• Journal of Welding and Joining
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• v.12 no.4
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• pp.117-126
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• 1994

APAL (Aramid Patched ALuminum alloy) was manufactured, which was a material that was consisting of a A12024-T3 aluminum alloy plate bonded to single-side of it with aramid/epoxy laminates. The aramid/epoxy laminates were bonded to it in condition of 1, 2 ply and fiber orientation of .+-.45, 0.deg./90.deg. Fatigue crack propagation tests were performed at stress ratio R-0.2, 0.5 with Al 2024-T3, APAL 45-1P, APAL 0/90-1P, APAL 45-2P, APAL 0/90-2P specimens to examine behavior of retardation in fatigue crack propagation. All the APAL specimens showed superior fatigue crack resistance. Number of cycle spended for crack to propagate from $a_{M}$=37 to $a_{M}$=65 mm in case of APAL 0/90-2P specimen was half that of Al 2024-T3 specimen. Fatigue crack propagation rate of APAL 0/90 specimens were retarded more compared to APAL 45 specimens and the amounts of retardation at R=0.5 were larger than that at R=0.2. It was found that the retardation in fatigue crack propagation was caused by intact fibers in the wake of crack.ack.