• 한국세라믹학회지
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• 제30권11호
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• pp.881-890
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• 1993

MAS system has narrow sintering temp. range due to the liquid phae sintering and thereby densify rapidly. And especially, its poor mechanical properties limitedthe industrial application. In this study, the improvement of mechanical properties and densification is suggested by the consideration of the toughening mechanisms and isolated pore generation mechanism which is derived by the liquid phase sintering theory in 3Y-TZP added composites. After Pressureless sintering up to 140$0^{\circ}C$ for 5hr, the dihedral angle and contact angle are analyzed by the observation of microstructure. As a result of microstructure analysis, the sintering stage of the specimen sintered for 5hr is analyzed as solid-skeleton stage. And the isolated pore generation mechanisms are considered as (1) The swelling of the liquid phase is predominent due to the facts that dihedral angle is larger than 60$^{\circ}$, contact angle is large and that liquid volume fraction is smaller than 10%. (2) The porous characteristics of the MAS system is also suggested as: the SiO2-rich liquid film is firstly formed at the srface and therefore this reduces the contiguity of the pore, which induces the isolated pore. The strength and fracture toughness increased with the addition of 3Y-TZP and the main fracture toughness improvement mechanisms are analyzed as the crack deflection.

• 대한족부족관절학회지
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• 제17권3호
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• pp.182-188
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• 2013

Purpose: We evaluate clinical manifestations and radiologic features of ankle fracture & dislocation, as well as the usefulness of computed tomography on posterior ankle fracture & dislocation to study factors contributing to ankle fracture & dislocation. Material and Methods: Ankle dislocation was defined as the center of talar body being translated over the cortex of tibia on AP or lateral view on simple X-ray. Surgical treatments of 30 patients from January 2007 to March 2012 were categorized according to the injury mechanism, the direction of dislocation and fracture site. Joint involvement of posterior malleoalr fracture was evaluated through simple x-ray and computed tomography. We treated surgically if posterior malleolus fracture involves more than 25% of dital tibial articular surface. Thereafter, clinical outcomes were identified through radiographs and by using the AOFAS score. Results: The mean age was 42(13-78) years old, and slip down was the most common injury mechanism (13 cases). Car accident (6 cases) and fall accident (4 cases) were the next frequently found injury mechanisms. As for the types of ankle fracture, posterior fracture and dislocation (21 cases, 43.3%) was most commonly found. Out of these 21 cases, 15 cases involved trimalleolar fracture, and 19 cases were associated with posterior malleolar fracture. Danis-weber type B and C patients were 11 cases and 10 cases respectively. Articular involvement of posterior malleolar fracture turned out to be average 27.9%(5.1%~49.1%) on simple x-ray. The rate was evaluated as average 31.7%(12.6%~55.3%) on computed tomography which was conducted 15 times, and led us to more meaningful data. Conclusion: Anterolateral fracture and dislocation often accompanied open dislocation. Posterior fracture dislocation was most commonly found. Posterior malleolus was an important factor that ensures posterior stability of the ankle joint. Computed tomograph is useful to evaluate the articular involvement of posterior malleolar fracture.

• 대한기계학회논문집A
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• 제22권3호
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• pp.611-623
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• 1998

The delamination fracture of multidirectional carbon-fiber/epoxy laminates under the Mode I condition has been studied using the modified beam analysis for a fracture mechanics approach. It was found that the variation of fracture energy $G_IC$ with increasing length of the propagating crack exhibited a minimum for the pure interlaminar fracture and a maximum for the intraply fracture,i.e. a rising "R-curve", which was strongly affected by the degree of fiber bridging and crack-tip splitting arising in the global delamination. The maximum $G_IC$ value was significantly dependent on such types of delamination as no crack jumping, crack jumping into the adjacent ply and edge-delamination. It was shown also that the value of "effective flexural modulus" estimated from the modified beam analysis increased much with the development of fiber bridging behind the crack tip.ehind the crack tip.

• 한국재료학회지
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• 제14권9호
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• pp.649-654
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• 2004

In this paper, the fracture toughness and mechanisms of failure in a random SiC-whisker/$Al_{2}O_3$ ceramic composite were investigated using in situ observations during mode I(opening) loading. $SiC_{w}/Al_{2}O_3$ composite was obtained by hot press sintering of $Al_{2}O_3$ powder and SiC whisker as the matrix and reinforcement, respectively. The whisker and powder were mixed using a turbo mill. The composite was produced at SiC whisker volume fraction of $0.3\%$. Compared with monolithic $Al_{2}O_3$, fracture toughness enhancement was observed in $SiC_{w}/Al_{2}O_3$ composite. This improved fracture toughness was attributed to SiC whisker bridging and crack deflection. $SiC_{w}/Al_{2}O_3$ composite exhibited typically brittle fracture behavior, but a fracture process zone was observed in this composite. This means that the load versus load-line displacement curve of $SiC_{w}/Al_{2}O_3$ composite from a fracture test may involve a small non-linear region near the peak load.

• 한국해양공학회지
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• 제10권4호
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• pp.75-83
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• 1996

Polymeric composites can be subjected to a wide variety of environmemtal conditions in practical use. One of most important conditions to be considered in the stuctural design using such materials is the miisture envirnment. Thus the moisture effect on interlaminar fracture toughness $G_IC$ and $G_IIC$ of CFRP(carbon fiber reinforced plastic) composed of carbon fibers and epoxy resin is studied in this paper. Specimens were first processed in 25, 50, $80^{\circ}C$ flesh water and $25^{\circ}C$ sea water for various periods of time. After that, the water absorption and fracture toughness tests were performed under laboratory atmosphere. As result, the specimen processed in $80^{\circ}C$ flesh water indicates the highest misture absorbing capability, the second in $50^{\circ}C$ flesh water, the third in $25^{\circ}C$ sea water, and the specimen in $25^{\circ}C$ flesh water does the lowest. The interlaminar fracture toughness $G_IC$ increases, approaches to the maximum, and decreases as the immersion time increases. In case of interlaminar $G_IIC$, the value of the specimen processed in $80^{\circ}C$ flesh water turns out to be higher than others. In addition, the scanning electron micrographs(SEM) of fracture surfaces were also examined in order to explain the mechanism of fracture.

• 대한족부족관절학회지
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• 제18권4호
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• pp.217-221
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• 2014

Fracture and fracture-dislocation of the ankle may be caused by a variety of mechanisms. In addition to the fracture, injury of soft tissue such as ligaments, tendons, nerves, and muscles may occur. Among these, tibialis posterior tendon injury is difficult to identify due to swelling and pain at the fracture site. There is no clear finding in radiological examination, therefore, it is found during surgery. In this case, irreducible fracture-dislocation of the ankle due to tibialis posterior tendon interposition was observed after the primary operation. The authors obtained satisfactory results in performance of a secondary operation assisted with arthroscopy.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.288-289
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• 2009

Using a mechano-luminescent (ML) material enabling the visualization of fast propagating cracks with bridging or transformed wake evolutions under a conventional loading condition, the quasi-dynamic fracture mechanisms in association with two different types of crack wake developments wewe investigated in various ceramic.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.836-843
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• 2003

The polymer composites contain numerous internal boundaries and its structural elements have different responses and different resistances under the same service environment. Fatigue phenomenon is much more complex in composites than homogeneous materials. An understanding of the fracture behavior of polymer composite materials subjected to constant and cyclic loading is necessary for predicting the life time of structures fabricated with polymers. There is a need to acquire a better understanding of the fatigue performance and failure mechanisms of composites under such conditions. Therefore, in this study the analyses of fiber orientation and fracture mechanism for low cycle fatigue crack have been studied by SEM and LM for observing the ultrathin sections.

• 한국안전학회지
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• 제6권3호
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• pp.50-55
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• 1991

It is well known that mechanisms of fracture and crack growth depend upon material characteristics such as fracture toughness, environmental condition, cracd geometry and mechanical properties. It seems to be very important to investihate the effects of the above factors on the behavior of structural components which contain flaws for the detailed evaluation of their intehrity. In this experimental research, fracture behaviors of moterials were investigated by using Acoustic Emission(AE) technique. The fracturing processes of materials were estimated through both the tension specimens. For the detrmlnatlon of yied strength or fracture toughness, the critical applied load at the crack initiation and propagation is thought to be very important. The critical applied load(PQ) was determined through AE signal. The source of AE signal was estimated by fractography analysis. These experimental results may contribute to the safety analyses and the evaluation of strength of structures.

• 대한기계학회논문집
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• 제18권6호
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• pp.1388-1398
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• 1994

The fracture toughness and micro-fracture mechanisms of the porous glass and stainless fiber reinforced glass composite were evaluated by using the acoustice mission(AE) technique, fracture toughness $test(K_{IC})$ and the macroscopic observation of the specimen surface which was being under the loading. At initial portion of the loading, the AE signals with low energy, of which origins were considered as the micro-cracks formated at the crack tip, were emitted. With increasing the applied load, AE signals having higher energies were generated due to the coalesence of micro-cracks and fast fracture. Based on the such relationship between AE emission and loading condition, fracture toughness $K_{IAE}$ could be defined successfully be using the $K_I$ value corresponding to an abrupt change of the accumulated AE signal energies emitted during the fracture toughness test. In spite of its brittleness of glass material, nonlinear deformation behavior before maximum load was observed due to the formation of micro-cracks. Further, the stainless fiber may have attributed to the improvement of fracture toughness and the resistance to crack propagation comparing to noncomposited materials Finally, models of the micro-fracture process combined with the AE sources for the porous glass material and its composite were proposed paying attention to the micro-crack nucleation and its coalescence at the crack tip. Fiber fracture and its Pullout, deformation of fiber itself were also delinated from the model.