• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.361-364
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• 2002

This paper discusses the influencing factors such as coring position, height to diameter ratio of core specimen(h/d) and coring torque on the strength estimation of concrete by small site coring method in order to verify the validities of small size core method. According to results, as for the influence of drilling position, when core specimens are obtained from the place parallel to placing direction, compressive strength of core specimens are higher than those perpendicular to placing direction. This is due to the loss of the area of core specimen perpendicular to plating direction by bleeding. And in case of $\phi$ 24mm core specimen, when vertical drilling against placing direction is taken. compressive strength of core specimen obtained at the bottom of the structure is higher than that at the top of the structure. As for the influence of height to depth ratio, as h/d ratio increases compressive strength shows to be decreased. As for the influences of rotation speed of drilling machine, as its speed goes up, compressive strength decreases, regardless of core diameter.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2002.11a
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• pp.51-54
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• 2002

This study is intended to investigate an influence of the kinds and the maximum size of aggregate on the compressive strength of small size core specimen. According to the results, the compressive strength of standard specimen is large in order of basalt, granite and limestone aggregate, and shows increasing tendency as the maximum size of aggregate grows large. The compressive strength of concrete using basalt aggregate shows similar tendency to granite aggregate, and that of concrete using limestone aggregate decreases slightly, compared with granite aggregate. The reducing ratio of the compressive strength of 25mm core specimen is least when the maximum size of aggregate is 10mm. But the compressive strength of 50 and 100mm core specimen is almost not influenced by the maximum size of aggregate.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.2
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• pp.197-207
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• 2001

Development of new ceramics and esthetic needs of patients increase the use of all ceramic restorations. Fractured teeth often need metal post and core as foundation for final restoration. When all ceramic restorations are planned, metal post and core may lead to compromised esthetics because of opacity and gray color of metal post and core. Many techniques have been proposed to solve this problem such as application of an opaque porcelain to the metal core or all ceramic post and core. This study was performed to evaluate effect on color of Empress 2 crown according to various post systems. Color was evaluated by the CIE $L^*a^*b^*$ systems and measured by spectrophotometer (Model CM-3500, Minolta, Japan). Specimens were divided into 4 groups as follows Group 1 : gold cast post specimen + Empress 2 crown specimen Group 2 : application of an opaque porcelain to gold cast post specimen + Empress 2 crown specimen Group 3 : cosmopost specimen + Empress 2 crown specimen Group 4 : In-ceram post specimen + Empress 2 crown specimen. The results obtained as follows, 1. $L^*$ Values showed that group 2, 3, 4 were higher than group 1 with significant difference and group 2, 3, 4 were not significantly different. 2. $a^*$ Values and $b^*$ values also showed that group 2. 3, 4 were higher than group 1 with significant difference and group 2, 3, 4 were not significantly different. 3. ${\Delta}E^* ab$ Values showed that ${\Delta}E^* ab$ 3 was the highest value and ${\Delta}E^* ab$ 5 was the lowest value.

• International Journal of Railway
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• v.4 no.4
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• pp.103-108
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• 2011

The effect of the core cell shape on shock absorption characteristics of biomimetically inspired honeycomb structures has been numerically investigated. The finite element models of honeycomb test specimen composed of five core cells of identical mass have been constructed, and numerical simulations have been run on PAMCRASH. The dimensions of the sides of core cells as well as the angle between the sides have been shown to influence the shock absorption characteristics of the honeycomb structure. The specimen with regular hexagonal core cell shape is found to show the best shock absorbing capacity, and specimen with rectangle-like core cell are found to provide good shock absorbing characteristics.

• Journal of Korean Association for Spatial Structures
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• v.23 no.1
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• pp.61-68
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• 2023

Buckling Restrained Braces can not only express the strength considered at the time of design, but also reduce the seismic load by energy dissipation according to the plastic behavior after yield deformation of the steel core. The physical characteristics and damping effect may be different according to the buckling prevention method of the steel core by the lateral restraint element. Accordingly, in this study, To compare hysteresis characteristics, Specimen(BRB-C) filled with mortar, specimen(BRB-R) combined with a buckling restraint ring and Specimen(BRB-EP) filled with engineering plastics was fabricated, and a cyclic loading test was performed. As a result of the cyclic loading test, the maximum compressive strength, cumulative energy dissipation and ductility of each test specimen was similar. But in case of the cumulative energy dissipation and ductility, BRB-C filled with the mortar specimen showed the lowest. This is considered to be because the gap between the steel core and the reinforcing material for plastic deformation was not uniformly formed by pouring mortar around the core part.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.316-319
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• 2008

The L-bending of inner-structure bonded sandwich sheet metal is examined by using a bending die attached to the material testing machine. The specimen is composed of top and bottom layers and a middle layer of pyramid-core structure and each layer is bonded by brazing. The variables chosen for experiments were clearance between punch and die, location of bend line on the specimen surface and clamping type of specimen during L-bending. Effects of these variables on deformation of specimen around die-corner radius were investigated. It was shown that the irregular shapes of recess are formed in the inner layer of bended parts and they greatly depend on working conditions.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.193-194
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• 2022

The use of high-strength grout for facility foundations and bridges has recently been expanding in offshore wind farms. Offshore wind farms require a bearing capacity for horizontal loads such as wind, waves. Therefore, in this study, the strength of the high-strength grout discharged through pump pressure was measured and compared with the existing strength to secure the strength after the underwater pump pressure of the high-strength grout used in the offshore wind connection. The compressive strength measurement showed that the strength difference at each position of the core specimen was 1% higher than that of the other specimens, and there was almost no change in the strength according to the height. The strength of the core specimen decreased by 23% compared to the existing strength, which is similar to the result of this study because the strength of the core specimen decreased by approximately 25% compared to the general specimen according to related research. Therefore, it is believed that there is no decrease in strength due to underwater pumping.

• 한국도로학회:학술대회논문집
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• 2000.11a
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• pp.205-209
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• 2000

• Restorative Dentistry and Endodontics
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• v.23 no.2
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• pp.690-700
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• 1998

Rubber-toughened particles which are used in the field of chemical engineering are used to increase the fracture toughness of thermoset resin. The application of Core-Shell particles, one of rubber-toughened particles, as a filler for dental composite or restoration have not been examined. The purpose of this study was to evaluate possible use of Core-Shell particles for dental composite, and the hypothesis was that additional toughening mechanisms are activated by the addition of Core-Shell particles. After blending 50vol% quartz with Bis-GMA/TEGDMA resin matrix, the experimental resins were made by the addition of Core-Shell particles with varied content level as 0, 2.5, 5, 7.5, 10, 12.5, 15, and 20wt%. Fracture toughness was determined on three-point bending specimen with single-edge notch according to ASTM-E 399. Also, flexural properties, that is, strength and modulus were measured by three-point bending testing. Fractogragh of fracture toughness specimen was observed using SEM (JEOL 6400 SEM, MA). The following results from this study were obtained ; 1. Fracture toughness of composite resin added 2.5wt% Core-Shell particles was significantly higher than control group ($p{\leq}0.05$). 2. Flexural properties were decreased with increasing Core-Shell particle content, which showed a correlation statistically ($p{\leq}0.05$). 3. A toughening mechanism such as lamination and microcrack was observed in specimen determined high fracture toughness. 4. The dispersion of Core-Shell itself and quartz filler particles was limited present high content of Core-Shell particles, which decreased a resulting mechanical properties of composites. These results suggest that adequate Core-Shell particles can be used to enhance mechanical properties included toughening for dental composites.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.05a
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• pp.79-82
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• 2008

It has been reported that destruction test by core collection is the most reliable of the structural concrete strength in present building construction field. But it causes low efficiency by damage and cutting in structure due to the core collection. It also has some problems in repairing. Additionally in case of strength test with management specimen, different environment compared to the structure environment cause problems about estimation precise structure strength. Therefore, it is required to develop structure direct strength test that has test values and credibility above the ones obtained by core specimen collection strength test and seasonal specimen test to suggest a reasonable and practical management method of structural concrete.