• Journal of Ocean Engineering and Technology
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• v.16 no.5
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• pp.66-72
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• 2002

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. Acoustic emission(AE) has been widely used in various fields because of its extreme sensitivity, dynamic detection ability and location of growing defects. In this study, we investigated failure modes of locally wall thinned pipes and AE signals by bending test. From test results, we could be divided four types of failure modes of ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. And fracture behaviors such as elastic region, yielding region, plastic deformation region and crack progress region could be evaluated by AE counts, accumulative counts and time-frequency analysis during bending test. The result of the frequency range is expected to be basic data that can inspect plants in real-time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1319-1327
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• 1994

Since fatigue cracks in rail can be the source of fractures and subsequent derailments, quantitative evaluation of the fatigue behavior and fracture properities due to the analysis results of laboratory test are drawn on the basis for predicting fatigue life and making a decision of safe inspection interval. Charpy V-notch and fracture toughness behavior were evaluated from the results of Charpy impact test. Fatigue test was performed by using CT type specimen under constant amplitude loading, and finally the effects of the following parameters; crack orientation, temperature, and stress ratio, on the fatigue crack growth behavior were studied.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.26-34
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• 2001

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

• Structural Engineering and Mechanics
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• v.19 no.5
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• pp.519-533
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• 2005

The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.326-330
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• 2004

Thermosetting matrix composites have disadvantages in terms of moulding time, repairability and manufacturing cost. Thus the high-performance thermoplastic composites to eliminate such disadvantages have been developed so far. As a result of environmental and economical concerns, there is a growing interest in the use of thermoplastic composites. However, since their mechanical properties are very sensitive to the environment such as moisture, temperature etc., those behaviors need to be studied. Particularly the temperature is a very important factor influencing the mechanical behavior of thermoplastic composites. The effect of temperature have not yet been fully quantified. Since engineering applications of reinforced composites necessitate their fracture mechanics characterization, work is in progress to investigate the fracture and related failure behavior. An approach which predicts the tensile strength was perpormed in the tensile test. The main goal of this work is to study the effect of temperature on the result of tensile test with respect to GF/PE composite. The tensile strength and failure mechanisms of GF/PE composites were investigated in the temperature range $60^{\circ}C\;to\;-50^{\circ}C$. The tensile strength increased as the fiber volume fraction ratio increased. The tensile strength showed the maximum at $-50^{\circ}C$, and it tended to decrease as the temperature increased from $-50^{\circ}C$. The major failure mechanisms was classified into the fiber matrix debonding, the fiber pull-out, the delamination and the matrix deformation.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.65-72
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• 2018

PURPOSE. The aim of this in vitro study was to investigate the fracture resistance under chewing simulation of implant-supported posterior restorations (crowns cemented to hybrid-abutments) made of different all-ceramic materials. MATERIALS AND METHODS. Monolithic zirconia (MZr) and monolithic lithium disilicate (MLD) crowns for mandibular first molar were fabricated using computer-aided design/computer-aided manufacturing technology and then cemented to zirconia hybrid-abutments (Ti-based). Each group was divided into two subgroups (n=10): (A) control group, crowns were subjected to single load to fracture; (B) test group, crowns underwent chewing simulation using multiple loads for 1.2 million cycles at 1.2 Hz with simultaneous thermocycling between $5^{\circ}C$ and $55^{\circ}C$. Data was statistically analyzed with one-way ANOVA and a Post-Hoc test. RESULTS. All tested crowns survived chewing simulation resulting in 100% survival rate. However, wear facets were observed on all the crowns at the occlusal contact point. Fracture load of monolithic lithium disilicate crowns was statistically significantly lower than that of monolithic zirconia crowns. Also, fracture load was significantly reduced in both of the all-ceramic materials after exposure to chewing simulation and thermocycling. Crowns of all test groups exhibited cohesive fracture within the monolithic crown structure only, and no abutment fractures or screw loosening were observed. CONCLUSION. When supported by implants, monolithic zirconia restorations cemented to hybrid abutments withstand masticatory forces. Also, fatigue loading accompanied by simultaneous thermocycling significantly reduces the strength of both of the all-ceramic materials. Moreover, further research is needed to define potentials, limits, and long-term serviceability of the materials and hybrid abutments.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.791-798
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• 2012

Since standardized fracture test specimens cannot be easily extracted from in-service components, several alternative fracture toughness test methods have been proposed to characterize the deformation and fracture resistance of materials. One of the more promising alternatives is the local approach employing the SP(Small Punch) testing technique. However, this process has several limitations such as a lack of anisotropic yield potential and tediousness in the damage parameter calibration process. The present paper investigates estimation of ductile fracture resistance(J-R) curve by FE(Finite Element) analyses using an anisotropic damage model and enhanced calibration procedure. In this context, specific tensile tests to quantify plastic strain ratios were carried out and SP test data were obtained from the previous research. Also, damage parameters constituting the Gurson-Tvergaard-Needleman model in conjunction with Hill's 48 yield criterion were calibrated for a typical nuclear reactor material through a genetic algorithm. Finally, the J-R curve of a standard compact tension specimen was predicted by further detailed FE analyses employing the calibrated damage parameters. It showed a lower fracture resistance of the specimen material than that based on the isotropic yield criterion. Therefore, a more realistic J-R curve of a reactor material can be obtained effectively from the proposed methodology by taking into account a reduced load-carrying capacity due to anisotropy.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.2
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• pp.158-163
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• 2003

Thermosetting matrix composites have disadvantages in terms of moulding time, repairability and manufacturing cost. Thus the high-performance thermoplastic composites to eliminate such disadvantages have been developed so far. As a result of environmental and economical concerns, there is a growing interest in the use of thermoplastic composites. However, since their mechanical properties are very sensitive to the environment such as moisture, temperature etc., those behaviors need to be studied. Particularly the temperature is a very important factor influencing the mechanical behavior of thermoplastic composites. The effect of temperature have not yet been fully quantified. Since engineering applications of reinforced composites necessitate their fracture mechanic characterization, work is in progress to investigate the fracture and related failure behavior. An approach which predicts the tensile strength was perpormed in the tensile test. The main goal of this work is to study the effect of temperature on the result of tensile test with respect to GF/PE composite. The tensile strength and failure mechanisms of GF/PE composites were investigated in the temperature range 6$0^{\circ}C$ to -5$0^{\circ}C$. The tensile strength increased as the fiber volume fraction ratio increased. The tensile strength showed the maximum at -5$0^{\circ}C$, and it tended to decrease as the temperature increased from -5$0^{\circ}C$. The major failure mechanism was classified into the fiber matrix debonding, the fiber pull-out, the delamination and the matrix deformation.

• Composites Research
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• v.35 no.2
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• pp.61-68
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• 2022

Composite materials have been used in aerospace industry and many applications because of many advantages such as specific strength and stiffness and corrosion resistance etc. However, it is vulnerable to impacts, these impact lead to formation of cracks in composite laminate and failure of structures. In this paper, we analyzed Mode I fracture toughness of Carbon/Epoxy laminates using acoustic emission signal. DCB test was carried out to analyze Mode I failure characterization of Carbon/Epoxy laminates, and AE sensor was attached to measure AE signal induced by failure of specimen. Fracture toughness was calculated using cumulative AE energy and measured crack length using camera. The calculated fracture toughness was applied in FE model and the result of FE analysis compared with DCB test results. The results show good agreement with between FEM and DCB test results.

• Journal of Wind Energy
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• v.14 no.3
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• pp.83-90
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• 2023

The purpose of this study is to evaluate the inter-laminar fracture toughness characteristics of CFRP pultrusion spar cap materials reinforced with non-woven glass fabric. Test specimens were fabricated by the infusion technique. A non-woven glass fabric and artificial defects were embedded on the middle surface between two pultruded CFRP panels. Double cantilever beam (DCB) and End Notched Flexure (ENF) tests were performed according to ASTM standards. Fracture toughness and crack propagation characteristics were evaluated with load-displacement curves and delamination resistance curves (R-Curve). The fracture toughness results were calculated by compliance calibration (CC) method. The initiation and propagation values of Mode-I critical strain energy release rate value G_Ic were 1.357 kJ/m2 and 1.397 kJ/m2, respectively, and Mode-II critical strain energy release rate values G_IIc were 4.053 kJ/m2 for non-precracked test and 4.547 kJ/m2 for precracked test. It was found that the fracture toughness properties of the CFRP pultrusion spar-cap are influenced by the interface between the layers of CFRP and glass fiber non-woven.