• International Journal of Safety
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• v.8 no.1
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• pp.6-9
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• 2009

The crack in a J85 engine V.G. actuator arm shaft for a bell crank on the engine compressor was investigated. The crack was observed in twenty two shafts during the inspection of 238 shafts. The failure analysis of shaft cracks was performed by chemical composition analysis using ICP(Inductively Coupled Plasma) and by fracture surface and microstructure analysis using FE-SEM and optical microscope. The crack initiated from the top and bottom and propagated to the center along the grain boundaries. From the chemical composition analysis, the fractography of the fracture surface and the microstructure, it was found that the failure mechanism of the shafts is the inclusion-related intergranular decohesion crack. The inclusion was found out from MnS particle by EDS(Energy Dispersive Spectroscopy). The crack initiated MnS inclusion in the grain boundary and propagated with the increase of applied shear stress during long operation. In order to prevent the fracture, NDI(Nondestructive inspection) is needed periodically as recommended.

• Computers and Concrete
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• v.1 no.4
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• pp.389-400
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• 2004

The examinations carried out have confirmed a relationship existing between the character of fracture surfaces and the composition and structure of (basalt and gravel) concretes. For both concretes investigated, a very good correlation was obtained between the profile line development factor, $R_L$, and the fracture surface development factor, $R_S$. With the increase in the $R_L$ parameter, the fracture surface development factor $R_S$ also increased. Agreement between the proposed relationship of $R_S=f(R_L)$ and the proposal given by Coster and Chermant (1983) was obtained. Stereological examinations carried out along with fractographic examinations made it possible to obtain a statistical model for the determination of $R_L$ (or $R_S$) based on the volume of air voids in concrete, $V_{air}$, the specific surface of air pores, $S_V_{air}$ the specific surface of coarse aggregate, $S_{Vagg.}$, and the volume of mortar, $V_m$. An effect of coarse aggregate type on the obtained values of the profile line development factor, $R_L$, as well as on the relationship $R_S=f(R_L)$ was observed. The increment in the fracture surface development factor $R_S$ with increasing $R_L$ parameter was larger in basalt concretes than in gravel concretes, which was a consequence of the level of complexity of fractures formed, resulting chiefly from the shape of coarse aggregate grains.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4647-4658
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• 2023

In this paper, elastic-plastic fracture mechanics analysis is performed to determine the critical crack sizes of the multipurpose canister (MPC) manufactured using austenitic stainless steel under dynamic loading conditions that simulate drop accidents. Firstly, dynamic finite element (FE) analysis is performed using Abaqus v.2018 with the KORAD (Korea Radioactive Waste Agency)-21 model under two drop accident conditions. Through the FE analysis, critical locations and through-thickness stress distributions in the MPC are identified, where the maximum plastic strain occurs during impact loadings. Then, the evaluation using the failure assessment diagram (FAD) is performed by postulating an external surface crack at the critical location to determine the critical crack depth. It is found that, for the drop cases considered in this paper, the principal failure mechanism for the circumferential surface crack is found to be the plastic collapse due to dominant high bending axial stress in the thickness. For axial cracks, the plastic collapse is also the dominant failure mechanism due to high membrane hoop stress, followed by the ductile tearing analysis. When incorporating the strain rate effect on yield strength and fracture toughness, the critical crack depth increases from 10 to 20%.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.4
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• pp.65-73
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• 2004

Fatigue crack growth from surface defects is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LPG/LNG fuel tank and other various structures. This paper attempts to analysis some practical or general problems such as the estimation of crack growth life to penetrate the plate thickness, based on fatigue crack growth a single surface flaw and the interaction of multiple flaws. An experiment on the coalescence of multiple undercuts was carried out under cyclic tension condition as a attempt to the analysis of multiple crack problems. It is noted that the fracture strength is characterized by the analogy to that in a single crack growth.

• Journal of the Korean Society for Railway
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• v.3 no.2
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• pp.77-83
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• 2000

This study proposes the integrity evaluation of the bogie frame using ultrasonic fractography analysis. Analysis objectives in this study are to investigate fracture planes of damaged zone by the A-scan method. The surface condition of fracture planes shows degree of degradation by the stress concentration. The detection of the natural defects in the bogie frame is performed using the characteristics of echodynamic pattern in ultrasonic signal. Results of ultrasonic testing agree fairly well with those of actual fracture plane. In quantitative fractography analysis, microstructures of actual fracture plane turned out to be intergranular and transgranular fracture. Proposed ultrasonic fractography analysis in this study can be used for the integrity evaluation of the bogie frame.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.64-75
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• 2003

This study presents a newly suggested test method of Mode II fracture toughness measurement called "Punch Through Shear Test" which was originally proposed by Backers and Stephansson in 2001. The purpose of this study is to check the validity of the suggested testing method by performing Mode II fracture toughness tests for Daejeon Granite. In addition, the optimal specimen geometry for the testing and the relation between Mode II fracture toughness and confining pressure were also investigated. Fractured surface was observed to be very smooth with lots of rock debris which came off fracture surface which obviously implies that the surface was sheared off. This confirms that Mode II fracturing actually occurred. In addition, numerical analyses including continuum analysis, particle flow code analysis and crack propagation simulations were performed. Results of these numerical analyses indicated that the cracks occurred in the specimen were predominantly in Mode II and these cracks led to failure of the test specimen. From this investigation, it can be concluded that the newly suggested "Punch Through Shear Test" method provides a reliable means of determining the Mode II fracture toughness. fracture toughness.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2055-2060
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• 2003

Striation is a typical pattern observed on the fatigue fracture surface and the spacing is known to correspond to a macroscopic fatigue crack growth rate, and many models for the predict in the formation of such striation have been proposed. However, these theories and methods can't be applied under random loading spectrum. In this study, the fatigue tests were carried out on aluminum alloy under random loading spectrum. The fatigue fracture surfaces were observed in the scanning electron microscope (SEM) and great quantities of SEM micrographs were synthesized and saved in computer system. The space and morphology of several large-scale striations, which are expected to from at the relatively greater load range in loading block, were observed. The crack length for each loading blocks was decided in consideration of regularity and repetition of those striations. It is shown that the applicability of fractographic methods on the fatigue fracture surface under random loading spectrum.

• Journal of the Korean Ceramic Society
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• v.36 no.7
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• pp.711-717
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• 1999

Biaxial fracture behavior of alumina specimens with the diameter of 20mm and four kinds of thickness of 1.9, 2.3, 2.6 and 2.8mm was studied by the ball-on-3-ball test and the fracture results were analyzed by he analysis of variance (ANOCA), The strength measured with the down speed prescribed in ASTM showed that the measured strength was not dependent on the thickness of the specimens. Equivalent radius and crack-braching number were observed to increase lineraly with the thickness of the specimens. The jog direction was observed to study the effect of grinding direction on surface flaws. It is though that the surface finishing with #600 grit diamond wheel did not affect the surface flaws of the specimens.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.461-467
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• 2000

This study proposes the integrity evaluation of bogie frame using ultrasonic waves-fractography analysis. Analysis objectives in this study are to investigate fracture planes of damaged zone by the A-scan method. The surface condition of fracture plane shows degree of degradation by stress concentration. The detection of the natural defects in bogie frame is performed using the characteristics of echodynamic pattern in ultrasonic signal. Results of ultrasonic testing agree fairly well with those of actual fracture plane. In quantitative fractography analysis, microstructures of actual fracture plane turned out to be intergranular and transgranular fracture, Proposed ultrasonic-fractography analysis in this study can be used for the integrity evaluation of the bogie frame

• The Journal of Advanced Prosthodontics
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• v.16 no.2
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• pp.115-125
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• 2024

PURPOSE. The purpose of this in vitro study was to investigate the fracture resistance, surface hardness, and color stain of 3D printed, CAD-CAM milled, and conventional interim materials. MATERIALS AND METHODS. A total of 80 specimens were fabricated from auto polymerizing polymethyl methacrylate (PMMA), bis-acryl composite resin, CAD-CAM polymethyl methacrylate resin (milled), and 3D printed composite resin (printed) (n = 20). Forty of them were crown-shaped, on which fracture strength test was performed (n = 10). The others were disc-shaped specimens (10 mm × 2 mm) and divided into two groups for surface hardness and color stainability tests before and after thermal cycling in coffee solution (n = 10). Color parameters were measured with a spectrophotometer before and after each storage period, and color differences (CIEDE2000 [DE00]) were calculated. The distribution of variables was measured with the Kolmogorov Smirnov test, and one-way analysis of variance (ANOVA), Tukey HSD, Kruskal-Wallis, Mann-Whitney U tests were used in the analysis of quantitative independent data. Paired sample t-test was used in the analysis of dependent quantitative data (P < .05). RESULTS. The highest crown fracture resistance values were determined for the 3D printed composite resin (P < .05), and the lowest were observed in the bis-acryl composite resin (P < .05). Before and after thermal cycling, increase in mean hardness values were observed only in 3D printed composite resin (P < .05) and the highest ΔE₀₀ value were observed in PMMA resin for all materials (P < .05). CONCLUSION. 3D printing and CAD-CAM milled interim materials showed better fracture strength. After the coffee thermal cycle, the highest surface hardness value was again found in 3D printing and CAD-CAM milled interim samples and the color change of the bis-acryl resin-based samples and the additive production technique was higher than the PMMA resin and CAD-CAM milled resin samples.