• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.373-388
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• 2010

Fracture causes serious problems in many instance of prosthetic failures. But it is hard to find the definite causes when fractures occur. Fractography encompasses the examination of fracture surfaces that contain features resulting from the interaction of the advancing crack with the microstructure of the material and the stress fields. All fractured specimens(implant retaining screw) retrieved from Gangneung-Wonju national university dental hospital for 3 years(from 2007 to 2009). After pretreatment of samples, the scanning electon microscope were used for surface examination and fracture analysis. In case of most of the fractured specimens, fracture took place by fatigue fracture and fractured surface represents fatigue striation. Fatigue striation indicate the progression of the crack front under cyclic loading, are characteristic of stage 2 crack growth. The site of crack initiation and stage 1 crack growth were not easily identified in any of the failure, presumably because of the complex microstructural features of the polycrystalline sample. In case of fractured by overload, dimpled or cleavage surface were observed. Using the interpretation of characteristic markings(ratchet mark, fatigue striation, dimple, cleavage et al) in fracture surfaces, failure events containing the crack origin, crack propagation, material deficiency could be understand. Using the interpretation of characteristic markings in fracture surfaces, cause and mechanism of fractures could be analyzed.

• The Journal of Engineering Geology
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• v.30 no.2
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• pp.147-160
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• 2020

Unsaturated hydraulic conductivity of near-surface unconsolidated layers depends on the physical properties and water content of the unconsolidated layers. So far, many studies have been conducted on the unsaturated hydraulic conductivity of near-surface unconsolidated layers. However, researches on hydraulic conductivity of unsaturated fractured rocks have been relatively rare. In relation to the construction of a low/intermediate level radioactive waste surface-disposal facility, this study compared and analyzed van Genuchten parameters (α, n) in the laboratory and the hydraulic conductivity obtained in field tests for fractured hornfels at a radioactive-waste disposal site of Korea. The relationship between the field hydraulic conductivity and van Genuchten parameters using data from the ten depth intervals of three boreholes resulted in that the correlation coefficient (R) between the hydraulic conductivity and the van Genuchten parameter α was 0.7607, showing positive correlation whereas the R between the hydraulic conductivity and the van Genuchten shape-defining parameter n was -0.8720, showing negative correlation. Hence, this study confirmed the relationship between the field hydraulic conductivity and the van Genuchten unsaturated functions for the unsaturated fractured hornfels.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.297-309
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• 2010

The objective of the present study was to perform a fracture analysis on fractured implant fixture after use in vivo and make clear the cause & mechanisms of failure. In case of fatigue fracture, the fractured surface represents fatigue striation. Fatigue striation indicate the progression of the crack front under cyclic loading, are characteristic of stage 2 crack growth. The site of crack initiation and stage 1 crack growth were not easily identified in any of the failure, presumably because of the complex microstructural features of the polycrystalline sample. In case of fractured by overload, dimpled or cleavage surface were observed. Using the interpretation of characteristic markings(ratchet mark, fatigue striation, dimple, cleavage et al) in fracture surfaces, failure events containing the crack origin, crack propagation, material deficiency could be understand.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.5
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• pp.502-513
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• 2001

The purpose of this study was to evaluate the effect of dentin pretreatment with Dentin Conditioner, Ultra-Etch, conditioner of Fuji Plus cement on the shear bond strength of resin-reinforced glass ionomer cements to dentin and analyze the fractured surfaces. To evaluate the bond strength, the extracted human teeth which had uniform area of exposed dentin were cemented with conventional glass ionomer cement, 3M $RelyX^{TM}$ Luting (Vitremer luting cement), Fuji Plus cement after dentin pretreatment. The shear bond strength was measured using the Universal testing machine (Instron Co., USA) with a crosshead speed of 1mm/m. The effect of dentin pretreatment was evaluated by observing pretreated dentin surfaces under the scanning electron microscope, measuring the shear bond strength and observing the fractured surfaces under the scanning electron microscope. The results were as follows : On the SEM observation of surface morphology, the specimens treated with Dentin Conditioner. Ultra-Etch and conditioner of Fuji Plus cement were removed the smear layer and funneled dentinal tubules in dentin surfaces. In $RelyX^{TM}$ Luting cement group, shear bond strength of pretreated group was significantly higher than control group. In Fuji Plus cement group and Fuji I group, regardless of the type of pretreatment agents, there was tendency of increase in the shear bond strength. On the SEM observation of fractured surfaces, as the shear bond strength increase, it were shown thicker cement layers and were not shown dentinal tubules According to these results. it were shown that dentin pretreatment have much effect on bonding states.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.49 no.1
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• pp.43-48
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• 2023

The biocompatibility and durability of implant fixtures are major concerns for dentists and patients. Mechanical complications of the implant include abutment screw loosening, screw fracture, loss of implant prostheses, and implant fracture. This case report aims to describe management of a case of fixture damage that occurred after screw fracture in a tissue level, internal connection implant and microscopic evaluation of the fractured fixture. A trephine bur was used to remove the fixture, and the socket was grafted using allogeneic bone material. The failed implant was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), which revealed a fractured fixture with both normal and irregular bone patterns. The SEM and EDS results give an enlightenment of the failed fixture surface micromorphology with microfracture and contaminated chemical compositions. Noticeably, the significantly high level of gold (Au) on the implant surface and the trace amounts of Au and titanium (Ti) in the bone tissue were recorded, which might have resulted from instability and micro-movement of the implant-abutment connection over an extended period of time. Further study with larger number of patient and different types of implants is needed for further conclusion.

• Journal of Welding and Joining
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• v.22 no.2
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• pp.3-7
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• 2004

재료에 단순 인장시험에 의해 구한 항복강도의 2/3의 축응력을 부가하면, 소성변형과 파괴는 일어나지 않지만, 상당한 사이클로 반복하여 부가하면, 파괴가 일어난다. 이것을 피로파괴라고 한다 대부분의 구조물이나 기계부품은 재료의 항복응력 이하의 반복하중을 받으면서 작동되므로, 피로파괴가 자주 발생한다.(중략)

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.117-127
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• 1991

The purpose of this study was to evaluate the effect of surface treatment of fractured metal-ceramic crown on bond strength of porcelain repair resin. The specimens were divided into two groups for metal specimens add five groups for porcelain specimens by surface treatment methods. the metal specimens were treated by 2 methods. : micro-sandblasting with $50{\mu}m$ aluminum oxide and grinding with diamond bur. The porcelain specimens were treated by 5 methods : micro-sandblasting with $50{\mu}m$ aluminum oxide, grinding with diamond bur, etching with porcelain etching agent, combination of micro-sandblasting and etching procedure, and combination of grinding and etching procedure. After surface treatment, each specimen was bonded with composite resin and the bond strength was measured and the surface texture was observed by scanning electromicroscope(SEM). The results were as follows : 1. There was significant difference in shear bond strength between metal specimen and prorcelain specimen. 2. Bood strength of metal specimens treated with diamond bur was higher than that treated with $50{\mu}m$ aluminum oxide sandblasting. 3. Bond strength of porcelain specimen treated with diamond bur was higher than that treated with $50{\mu}m$ aluminum oxide sandblasting and porcelain etching agent. 4. There was no significant difference in shear bond strength between the group treated with diamond bur and combined treatment groups respectively. 5. The large undercuts were observed in group treated with diamond bur by SEM.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.3
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• pp.12-21
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• 2022

Directed energy deposition (DED) was adopted as a metal additive manufacturing method to develop a mold for the hot stamping process. The test piece was machined from Heatvar laminate material, and results were obtained through microstructure and defect observations, as well as hardness, tensile strength, and joint strength tests. 1) Spherical pores and irregular-shaped cavities were observed as lamination defects, and columnar dendrites formed in the structure, which tended to become coarse upon heat treatment. 2) The hardness of the heat-treated material (480HV) was slightly lower than that of the non-heat-treated material (500HV). 3) In the tensile test, the maximum tensile stress and strain of the heat-treated material were 1392 MPa and 15%, respectively, which were slightly higher than the values of 1381 MPa and 13%, respectively, for the non-heat-treated material. 4) In the case of the early final fracture in the tensile test, in most cases, pores or irregularly shaped cavities were observed at the fracture surface or near the surface. 5) In the joint strength test, most of the specimens finally fractured in the laminated metal area, and the fracture surface was intragranular. In addition, dimples formed over the entire area on the fracture surface of the fractured specimen after sufficient elongation.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.20-32
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• 2003

To understand the behavior of migration of contaminants in a fractured porous medium is a key to assure the overall safety of a potential radwaste repository. The feasible retention mechanism of contaminant transport in a tinctured medium are sorption of contaminants on solid surface and matrix diffusion of contaminants from a fracture into an adjacent porous medium. The acceleration mechanisms are the migration of contaminants in the form of pseudo-colloids and the limit of a volume f3r matrix diffusion. In this paper, the effects of these two acceleration mechanisms are studied mathematically, then semi-analytically computed by the application of the Talbot theorem and verified. Results indicate that the acceleration processes cannot be neglected in the modeling of contaminant transport in a fractured porous medium.

• Restorative Dentistry and Endodontics
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• v.16 no.2
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• pp.1-17
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• 1991

The purpose of this study was to analyze the in vivo amalgam corrosion products qualitatively. 30 molars with large, intact amalgam restorations were selected. All the restorations were more than 5 years old. Twenty of the removed amalgams were embedded in acrylic resin block. The exposed surfaces of fifteen embedded amalgams were polished by amalgam polishing kit, and the rest were observed without polishing. The remaining 10 amalgams were fractured centrally and perpendiculary to the occlusal surface with a wire-cutter. After all specimens were cleaned ultrasonically in distilled water, each surface was examined under S.E.M. and E.D.A.X. (Energy Dispersive Micro X-ray Analyzer) to determine the morphology and chemical nature of the corrosion products. The following results were obtained: 1. The surfaces of the unpolished amalgam restorations were covered with thin amorphous layer of Sn-Ca-P-S complex with numerous cracks. 2. In the conventional amalgams, the major corrosion products were Sn-Cl phases however, tin oxide phases were also observed. 3. Only tin oxide phase was identified in the high copper amalgam, but it was less frequently observed than in the conventional amalgam. 4. It was easier to observe the corrosion product morphology in the fractured surfaces than in the polished ones. The morphologies of the corrosion product crystals looked like a stack of slightly bended plates in the Sn-Cl phases and polyhedra or polygonal prisms in the tin oxide phases.