• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.3
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• pp.287-293
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• 2011

The enamel, the upper layer of a tooth has remarkable capability of bearing severe loading on the tooth. The fracture behavior is important to understand the mechanism of load bearing and it could be very useful for developing new materials. Non-destructive evaluation of such materials will also benefit from this knowledge. The graded microstructures of enamel were modeled by finite element analysis software and the J-integrals and the stress intensity factors were evaluated as the fracture parameters. The results show that these parameters are location dependent. Those values increase when measured in the direction of dentine enamel junction. This finding matched well with experiments and implies many useful understanding of biomaterials and applications to new materials.

• Journal of Ocean Engineering and Technology
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• v.2 no.1
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• pp.150-162
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• 1988

The dynamic fracture toughness, $K_{Id}$,is measured in the heat-treated and ion-nitrided Cr-Mo, Ni-Cr-Mo steel using standard and Precracked Charpy specimens an imstrumented impact machine. The value of $K_{Id}$and both the energy of initiate fracture, and the total energy of fracture. Since the $K_{Id}$values of the precraked impact specimens are in accord with their theoretical ones, this testing method is sufficently practical. The effect of ion-nitriding are found to be larger than the heat-treaded specimen.

• Restorative Dentistry and Endodontics
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• v.15 no.2
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• pp.17-33
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• 1990

The purpose of this study was to evaluate the fracture toughness of dental composite resins and to investigate the filler factor affecting the fracture behaviour on which the degree of fracture toughness depends. Six kinds of commercially available composite resin;, including two of each macrofilled, microfilled, and hybrid type were used for this study, The plane strain fracture toughness ($K_{10}$) was determined by three-point bending test using the single edge notch specimen according to the ASTM-E399. The specimens were fabricated with visible light curing or self curing of each composite resin previously inserted into a metal mold, and three-point bending test was conducted with cross-head speed of 0.1mm/min following a day's storage of the specimens in $37^{\circ}C$ distilled water. The filler volume fractions were determined by the standard ashing test according to the ISO-4049. Acoustic Emission(AE), a nondestructive testing method detecting the elastic wave released from the localized sources In material under a certain stress, was detected during three-point bending test and its analyzed data was compared with, canning electron fractographs of each specimen. The results were as follows : 1. The filler content of composite resin material was found to be highest in the hybrid type followed by the macrofilled type, and the microfilled type. 2. It was found that the value of plane strain fracture toughness of composite resin material was in the range from 0.69 MPa$\sqrt{m}$ to 1 46 MPa$\sqrt{m}$ and highest In the macrofilled type followed by the hybrid type, and the microfilled type. 3. The consequence of Acoustic Emission analysis revealed that the plane strain fracture toughness increased according as the count of Acoustic Emission events increased. 4. The higher the plane strain fracture toughness became, the higher degree of surface roughness and irregularity the fractographs demonstrated.

• Advances in concrete construction
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• v.2 no.2
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• pp.145-162
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• 2014

In this study, the fracture toughness $K_{IC}$ of high performance concrete (HPC) was determined by conducting three-point bending tests on eighty notched HPC beams of $500mm{\times}100mm{\times}100mm$ at high temperatures up to $450^{\circ}C$ (hot) and in cooled-down states (cold). When the concrete beams exposed to high temperatures for 16 hours, both thermal and hygric equilibriums were generally achieved. $K_{IC}$ for the hot concrete sustained a monotonic decrease tendency with the increasing temperature, with a sudden drop at $105^{\circ}C$. For the cold concrete, $K_{IC}$ sustained a two-stage decrease trend, dropping slowly with the heating temperature up to $150^{\circ}C$ and rapidly thereafter. The fracture energy-based fracture toughness $K_{IC}$' was found to follow similar decrease trends with the heating temperature. The weight loss, the fracture energy and the modulus of rapture were also evaluated.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.385-396
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• 2012

Thermal shock test methods and thermal shock parameters for ceramics were reviewed from the following viewpoints: (1) The test methods should be based on the precise estimation of both temperature and thermal stress distributions in a specimen taking into account the temperature-dependent thermo-mechanical properties; (2) The thermal shock parameters must be defined as a physical property of the materials and described as a function of temperature at the fracture point of the specimen; (3) The relation between the strength and fracture toughness of brittle ceramics under a thermal shock load must be the same as the relation under a mechanical load. In addition, appropriate thermal shock parameters should be defined by the thermal shock strength and thermal shock fracture toughness based on stress and energy criteria, respectively. A constant heat flux method is introduced as a testing technique suitable for estimating these thermal shock parameters directly from the electric power charged.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.161-166
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• 2008

In general structures, cleavage fracture may develop under the low constraint condition of larger scale yielding with a shallow surface crack. However, standard procedures for fracture toughness testing require very severe restrictions of specimen geometry. So the standard fracture toughness data makes the integrity assessment irrationally conservative. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 mm) with varying crack depth, The constraint effects on the crack depth ratios are quantitatively evaluated by scaling model and Weibull stress method using 3-D finite clement method, After correction of constraint loss due to shallow crack depths, the statistical size effect are also corrected according to the standard ASTM E 1921 procedure, The results snowed a good agreement in the geometry correction regardless of the crack size, while some over-corrections were observed in the corrected values of $T_0$.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1732-1741
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• 2020

The structural integrity of welded joints in the reactor pressure vessel (RPV) is directly related to the safety of nuclear power plants. The RPV is made from SA508-III steel in a pressurized water reactor. In this study, we investigated the effects of temperature on the tensile and fracture toughness properties of Chinese SA508-III welded joint in different sampling areas in order to provide reference data for structural integrity assessments of RPVs. The specimens used in tensile and fracture toughness tests were fabricated from the base metal (BM), weld metal (WM), and the heat-affected zone (HAZ) in the welded joint. The representative testing temperatures included the ambient temperature (20 ℃), upper shelf temperature (100 ℃), and service temperature (320 ℃). The results showed that temperature greatly affected the fracture toughness (JIC) values for the SA508-III welded joint. The JIC values for BM and HAZ both decreased remarkably from 20 ℃ to 320 ℃. The fracture morphologies showed that the BM and HAZ in the welded joint exhibited fully ductile fracture at 20 ℃, whereas partial cleavage fracture was mixed in ductile fracture mode at 100 ℃ and 320 ℃. The WM exhibited the ductile and cleavage fracture mixed mode at various temperatures, and the JIC values showed slight changes.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.277-290
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• 1995

The study was carried out to analyze the fracture behavior and the acoustic emission(AE) characteristics and to find the relationship among tensile strength, fracture toughness and cure pressure in owe process of the carbon fiber reinforced composites of two types, $[0^{\circ}/90^{\circ}]_{2S}$ and $[0^{\circ}\;_2/90^{\circ}\;_2]_S$. AE signals were detected during the curing process, tensile tests and fracture toughness tests by acoustic emission(AE) measurements, respectively. Tensile strengths showed that the less cure pressurizing steps and the side of $[0^{\circ}/90^{\circ}]_{2S}$ specimens had the higher strengths than those of the others. Fracture toughness by the change of test temperature showed nearly same values in the same temperature region, but the higher test temperature had the lower fracture toughness values. In order to examine the relationship between fracture behavior of CFRP in tensile and fracture toughness tests and AE signals, the post processing for AE parameters of AE data and the observations of microscope and SEM have been carried out respectively.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.219-223
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• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• Journal of dental hygiene science
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• v.18 no.1
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• pp.42-49
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• 2018

The computer-aided design/computer-aided manufacturing (CAD/CAM) system was introduced to shorten the production time of all-ceramic restorations and the number of patient visits. Among these types of ceramic for dental CAD/CAM, they have been processed into inlay, onlay, and crown shapes using leucite-reinforced glass-ceramics to improve strength. The purpose of this study was to observe the mechanical properties and microstructure of leucite-reinforced glass-ceramics for dental CAD/CAM. Two types of leucite-reinforced glass-ceramic blocks (IPS Empress CAD, Rosetta BM) were prepared with diameter of 13 mm and thickness of 1 mm. Biaxial flexural testing was conducted using a piston-on-three-ball method at a crosshead speed of 0.5 mm/min. Weibull statistics were used for the analysis of biaxial flexural strength. Fracture toughness was obtained using an indentation fracture method. Specimens were observed by field emission scanning electron microscopy to examine the microstructure of the leucite crystalline phase after acid etching with 0.5% hydrofluoric acid aqueous solution for 1 minute. The results of strength testing showed that IPS Empress CAD had a mean value of $158.1{\pm}8.6MPa$ and Rosetta BM of $172.3{\pm}8.3MPa$. The fracture toughness results showed that IPS Empress CAD had a mean value of $1.28{\pm}0.19MPa{\cdot}m^{1/2}$ and Rosetta BM of $1.38{\pm}0.12MPa{\cdot}m^{1/2}$. The Rosetta BM sample exhibited higher strength and fracture toughness. Moreover, the crystalline phase size and ratio were increased in the Rosetta BM sample. The above results are expected to elucidate the basic mechanical properties and crystal structure characteristics of IPS Empress CAD and Rosetta BM. Additionally, they will help develop leucite-reinforced glass-ceramic materials for CAD/CAM.