• Advanced Composite Materials
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• v.16 no.1
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• pp.11-30
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• 2007

Since delamination often propagates at the interfacial layer between a surface skin and a foam core, a crack arrester is proposed for the suppression of the delamination. The arrester has a semi-cylindrical shape and is arranged in the foam core and is attached to the surface skin. Here, energy release rates and complex stress intensity factors are calculated using finite element analysis. Effects of the arrester size and its elastic moduli on the crack suppressing capability are investigated. Considerable reductions of the energy release rates at the crack tip are achieved as the crack tip approached the leading edge of the crack arrester. Thus, this new concept of a crack arrester may become a promising device to suppress crack initiation and propagation of the foam core sandwich panels.

• Tunnel and Underground Space
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• v.2 no.2
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• pp.251-264
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• 1992

In this study, the size effect in measuring the fracture toughness of rock was investigated using the ISRM Suggested Method for Fracture toughness using Chevron Bend Specimens. Total 58 specimens were prepared with 4 different diameters, 29, 42, 54, 68mm and center cut-chevron notch. In addition to this, to evaluated the effect of anisotropy of Jecheon granite, which is the sample for this study, core drilling direction was adjusted perpendicular(short transverse) and parallel(arrester) to the rift plane in the sample and the measured fracture toughness for each direction were compared. Important results obtained from this study are as follows. Level ll test condition is more adequate than l, because of low data scattering and precision and corrected fracture toughness of Jechoen granite measured and 2.2MPa{{{{ SQRT { m} }}}} for arrester direction with minimum initial crack length 0.7cm. From the relationship between core diameter and initial crack length presented in the ISRM testing method, the specimen diameter should be bigger than 47mm. The fracture toughnesses measured for arrester and short transverse directon show 10% difference. This is to the anisotropy of Jecheon granite possessing rift plane.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.57-67
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• 2019

Water-induced strength reduction is one of the most critical causes for rock deformation and failure. Understanding the effects of water on the strength, toughness and deformability of rocks are of a great importance in rock fracture mechanics and design of structures in rock. However, only a few studies have been conducted to understand the effects of water on fracture properties such as fracture toughness, crack propagation velocity, consumed energy, and microstructural damage. Thus, in this study, we focused on the understanding of how microscale damages induced by water saturation affect mesoscale mechanical and fracture properties compared with oven dried specimens along three notch orientations-divider, arrester, and short transverse. The mechanical properties of calcite-cemented sandstone were examined using standard uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests. In addition, fracture properties such as fracture toughness, consumed energy and crack propagation velocity were examined with cracked chevron notched Brazilian disk (CCNBD) tests. Digital Image Correlation (DIC), a non-contact optical measurement technique, was used for both strain and crack propagation velocity measurements along the bedding plane orientations. Finally, environmental scanning electron microscope (ESEM) was employed to investigate the microstructural damages produced in calcite-cemented sandstone specimens before and after CCNBD tests. As results, both mechanical and fracture properties reduced significantly when specimens were saturated. The effects of water on fracture properties (fracture toughness and consumed energy) were predominant in divider specimens when compared with arrester and short transverse specimens. Whereas crack propagation velocity was faster in short transverse and slower in arrester, and intermediate in divider specimens. Based on ESEM data, water in the calcite-cemented sandstone induced microstructural damages (microcracks and voids) and increased the strength disparity between cement/matrix and rock forming mineral grains, which in turn reduced the crack propagation resistance of the rock, leading to lower both consumed energy and fracture toughness ($K_{IC}$).

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.2
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• pp.42-48
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• 2006

In order to assess the validity of fatigue crack arrest design charts obtained from our previous numerical approach to fatigue crack arrest condition, an extensive fatigue crack growth/arrest test was performed using CT-type integrally stiffened panels. The results are presented as fatigue crack growth rate and non-dimensional crack length relationship, and these are compared with numerically simulated crack growth rates. The measured values of da/dN at the moment of fatigue crack arrest occurred in stiffened panels are good agreement with those numerically simulated crack growth rates.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.6
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• pp.269-275
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• 2005

Ni/Ni-aluminide/Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured by thin foil hot press technique. Thick intermetallic layers of NiAl and $TiAl_3$ were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous taters of $Ni_3Al$ and TiAl were formed by a solid-state diffusion. Fracture resistance with loading along the crack arrester direction is higher than crack divider direction due to the interruption of crack growth in metal layers. The $Ni_3Al$ and NiAl intermetallic layer showed cleavage and intergranular fracture behavior, respectively, while the fracture mode of $TiAl_3$ layer was found to be an intragranular cleavage. The debonding between metal and intermetallic layer and the pores were observed in the Ni/Ni-aluminide layers, resulting in the lower fracture resistance. With the results of acoustic emission (AE) source characterization the real time of failure and the effect of AE to crack growth could be monitored.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.303-315
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• 1998

Four types of repair procedures are applied to the fatigue cracked crane runway gilders, which are stop-holes as crack arrester stop-holes reinforced with high strength bolts, welding repair and reinforcement with high strength bolted splices. The fatgiue cracks are reinitiated at the region where stop-holes and weld repairments are applied, while none of the cracks are observed in the cases of stop-holes reinforcement and reinforcement with high strength bolted splices. When using stop-holes and hole-reinforcement all repaired regions show a same fatigue strength to the one before the repairments. The experiments also reveal that the proper weldment is an essential factor when applying the welding repairement as a properly welding produces the same level of fatigue strength after the repairement. When the situation permits to use reinforcement with high strength boilted splices, the experiments shows the repairment is the best possible method among the procedures available.