• The Journal of Engineering Geology
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• v.12 no.3
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• pp.273-284
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• 2002

The purpose of this study is to characterize damage propagation in granite which exists in South Korea. Coarse, medium and fine-grained granite specimens were sampled respectively In order to perform this study, elastic wave velocity test and permeability test were carried out to estimate the physical specificities of specimens before and after damage. Cellulose acetate film duplication method was used to select only cracks from cross section and to make these visible. Using dark-field illumination, approach photographing technique was used to get more distinct photographs of cracks from acetate peel. Computer programs named Photoshop were used to describe cracks. After damage, coarse and medium-grained granite had lower elastic wane velocity, higher permeability, more cracks and more distinct shear fractures than fine-grained granite.

• Explosives and Blasting
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• v.36 no.3
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• pp.1-9
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• 2018

This study was conducted to evaluate the influences of the angle of artificial joints, the distance between the artificial joints and the blast hole, and the number of artificial joints on the pressure wave propagation, crack propagation, and blast wave velocity. The evaluation was conducted numerically by use of the Euler-Lagrange solver supported by the AUTODYN, which is a dynamic FEM program. As a result, it was found that the blast wave velocity was decreased most rapidly as either the distance between the artificial joint and the blast hole was decreased or the angle of the artificial joint was increased. In contrast to the case of no artificial joint, the amount of attenuation of the blast wave velocity was considerably large when an artificial joint was present. However, the effect of the number of artificial joint on the attenuation of the blast wave velocity was negligible under the given condition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.454-462
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• 1998

Mechanisms and conditions for rounding of AUC particles were examined during AUC precipitation. Rounding of AUC particle was possible only by external circulation using pump, not by internal circulation using agitator. The rate of AUC rounding $(dn_p/dt)$ was proporational to operation conditions such as magma density $(M_t:g-U/{\iota}l)$, turn over ratio $(T_o)$ and impeller tip velocity of pump (U); $ dn_p/dt{\propto}M_t{\cdot}T_o{\cdot}U^2$. The validity of this relationship was qualitatively confirmed by comparing the expermental results. Two rounding mechanisms were suggested. One is crack formation mechanism and the other etch-pit formation mechanism on the surface of AUC particle. It was found that the crack formation is more dominant at the initial stage and the etch-pit formation at the final stage of the AUC precipitation.

• Journal of Ocean Engineering and Technology
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• v.23 no.2
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• pp.69-73
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• 2009

The objective of this study was to obtain a better understanding of the delayed hydride cracking (DHC) of Zr-2.5Nb alloy. The DHC model has some defects: first, it cannot explain why the DHC velocity (DHCV) becomes constant regardless of an applied stress intensity factor, even though the stress gradient is affected by the applied stress intensity factor at the notch tip. Second, it cannot explain why the DHCV has a strong dependence on the method of approaching the test temperature by a cool-down or a heating-up, even under the same stress gradient, and third, it cannot predict any hydride size effect on the DHC velocity. The DHC tests were conducted on Zr-2.5Nb compact tension specimens with the test temperatures reached by a heating-up method and a cool-down method. Crack velocities were measured in hydrided specimens, which were cooled from solution-treatment temperatures at different rates by being furnace-cooled, water-quenched, and liquid nitrogen-quenched. The resulting hydride size, morphology, and distributions were examined by optical metallography. It was found that fast cooling rates, which produce very finely dispersed hydrides, result in higher crack growth rates. This different DHC behavior of the Zr-2.5Nb tube with the cooling rate after a homogenization treatment is due to the precipitation of the $\gamma$-hydrides only in the water-quenched Zr-2.5Nb tube. This experiment will provide supporting evidence that the terminal solid solubility of a dissolution (TSSD) of $\gamma$-hydrides is higher than that of $\delta$-hydrides.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.363-372
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• 2004

Double torsion (DT) tests were carried out to investigate the influence of the geometry of guide groove on stress corrosion index of Kumamoto andesite. The fracture toughness was measured in the constant displacement rate, which was set to 2.07 MN/m$^{3}$2/ in average regardless of crack velocity. Stress corrosion indices, n were evaluated using specimens with rectangular, circular and triangular grooves and were 37, 36 and 38 in average, respectively. The n values were constant regardless of the groove geometry, however the DT specimen with triangular groove geometry showed the largest standard deviation in the relationship between crack velocity and stress intensity factor. The DT test was found to be effective in using a rectangular-grooved specimen and the width of the groove must be greater than the average grain size of minerals.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.156-164
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• 2003

STS316L had been used as the structural material for energy environmental facilities, because austenite stainless steels like 316L have superior mechanical properties of which toughness, ductility, corrosion resistant and etc. However, those welded structures are receiving severe damage due to increasing of the aged degradation. Most studies until now have been carried out against fatigue behaviors of weldments, and were not well studied on nondestructive evaluation methods. In this study, the fatigue crack propagation behavior of STS316L weldment usually used for vessels of the nuclear power plant was investigated. Also, the degradation characteristics of 316L stainless steel weldments were evaluated by the ultrasonic parameter such as ultrasonic velocity, attenuation factor and time-frequency analysis. The results of this study can be used as a basic data for the prediction of the fatigue crack life of weldments structures without disjointing or stopping service of structures in service.

• Journal of Conservation Science
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• v.29 no.1
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• pp.35-45
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• 2013

The Clay Statues of Donggwanwangmyo Shrine (Treasure No. 142) are highly damaged physical weathering which are crack, exfoliation. Pigment of surface are discolored by chemical weathering like dust. The result of ultrasonic velocity measurement, low velocity zone was measured the lowest part of Woojanggun Statue. Deficiency condition of pigment layer was evaluated quantitatively through infrared Thermography. As a result, exfoliation part was detected at high temperature. Making techniques of the Clay statues were identified by gamma rays, infrared TV, SEM. All Clay Statues were founded on wood base and joints of wood were fixed using thin iron wires. After wood base was twisted a straw rope, it was made by clay. Clay was blended with rice straw to prevention of crack and exfoliation. The upper side of clay layer was coated with Hanji(Korean handmade paper) and cotton in order to isolate the pigment layer.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.169-177
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• 2011

In this study, an impact resistance of concrete segmented composites adopted shell's structures which have the excellent impact resistance was assessed. In order to enhance the performances of concrete segmented composite, the bond strength of mortar between the concrete blocks should be improved. Hence, in this study polymer mortars were applied to increase the bond strength of mortar. From the results of bond tests, the 15% latex mortar was selected and static and low-velocity impact tests were carried out for the specimens applied the plain and latex mortar. The concrete segmented composites, of which the bond strength of mortar was enhanced, showed improved low-velocity impact resistances. A Nonlinear finite element analysis using the discrete crack model showed similar energy dissipating capacities to the impact test's results. Consequently, by improving the analysis models for segmented composites, the impact resistances for manifold variables can be predicted and assessed.

• Journal of Conservation Science
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• v.30 no.4
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• pp.427-438
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• 2014

To measure the depth and extension on the surface cracks of the stone monument, ultrasonic pulse velocity targeted at the Mulgyeseowon Stele in Changnyeong was used in this research. Additionally, to establish a long-term countermeasure of management and conservation for this stele, we have investigated the material properties and damage on it and have conducted a precise diagnosis by a variety of non-destructive techniques. Our research has revealed that stones of the stele are composed mainly of three rock types according to the parts of it, alkali-feldspar granite, gabbro and diorite. The result of the deterioration evaluation has occurred that cracks, which are observed from every direction in the body of the stele, are the significant factors to reduce structural stability. The ultrasonic velocity for an evaluation on the properties of the stele has revealed that the speed was high in the order of body, pedestal and crown. Furthermore, to understand the present condition and occurrences of the cracks which have measured in many different forms on the stele quantitatively, we have estimated from 0.6 to 24.1cm deep of the cracks by To-Tc method using ultrasonic velocity.

• Earthquakes and Structures
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• v.8 no.3
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• pp.665-679
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• 2015

The strain rate of reinforced concrete (RC) structures stimulated by earthquake action has been generally recognized as in the range from $10^{-4}/s$ to $10^{-1}/s$. Because both concrete and steel reinforcement are rate-sensitive materials, the RC beam-column joints are bound to behave differently under different strain rates. This paper describes an investigation of seismic behavior of RC beam-column joints which are subjected to large cyclic displacements on the beam ends with three loading velocities, i.e., 0.4 mm/s, 4 mm/s and 40 mm/s respectively. The levels of strain rate on the joint core region are correspondingly estimated to be $10^{-5}/s$, $10^{-4}/s$, and $10^{-2}/s$. It is aimed to better understand the effect of strain rates on seismic behavior of beam-column joints, such as the carrying capacity and failure modes as well as the energy dissipation. From the experiments, it is observed that with the increase of loading velocity or strain rate, damage in the joint core region decreases but damage in the plastic hinge regions of adjacent beams increases. The energy absorbed in the hysteresis loops under higher loading velocity is larger than that under quasi-static loading. It is also found that the yielding load of the joint is almost independent of the loading velocity, and there is a marginal increase of the ultimate carrying capacity when the loading velocity is increased for the ranges studied in this work. However, under higher loading velocity the residual carrying capacity after peak load drops more rapidly. Additionally, the axial compression ratio has little effect on the shear carrying capacity of the beam-column joints, but with the increase of loading velocity, the crack width of concrete in the joint zone becomes narrower. The shear carrying capacity of the joint at higher loading velocity is higher than that calculated with the quasi-static method proposed by the design code. When the dynamic strengths of materials, i.e., concrete and reinforcement, are directly substituted into the design model of current code, it tends to be insufficiently safe.