• Proceedings of the KSME Conference
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• 2000.04a
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• pp.85-90
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• 2000

The fracture toughness and crack propagation behaviors of short nylon66 fiber reinforced Chloroprene rubber nave been Investigated as functions of fiber aspect ratio, fiber content and interphase conditions. The J for crack initiation and rupture were determined for short-fiber reinforced rubber. The values of $J_c$ for most reinforced rubbers were low compared that of matrix. But, $J_r$ at rupture showed a higher value than that of matrix. The crack propagation behaviors were analyzed into 3 patterns with increasing fiber aspect ratio and fiber content. The tearing mechanisms of matrix and fiber reinforced rubber were observed by CCD camera focused on the tip of crack and load-displacement graph. Both cases showed a completely different behaviors

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1257-1265
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• 1998

Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

• Structural Engineering and Mechanics
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• v.12 no.4
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• pp.377-396
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• 2001

The excessive cracking of RC cantilever decks, which often requires special attention for structural engineers, is studied using a three-dimensional crack analysis model. The model is based on a fracture energy approach for analyzing cracks in concrete, and the numerical analysis is carried out using a modified load control method. The problem of excessive cracking is then studied with four different span-ratios. Based on the numerical results, the crack behavior with respect to the patterns of crack propagation, dissipation of the fracture energy, and effects on the structural integrity are discussed. The mechanisms which cause the excessive cracking are also explained.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.535-543
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• 2004

Purpose: The purpose of this study is to compare the effect of two fiber post systems and one metal cast post system on the fracture strength and fracture pattern of crowned, endodontically treated teeth with 2 mm-height of the reamining tooth structure. Materials and methods: A total of 36 recently extracted sound human mandibular premolars were selected Each tooth structure of the crown portion except 2mm-height of the one above the cementoenamel junction was removed. After being endodontically treated, they were randomly distributed into 3 groups: group 1, restored with quarts fiber post(D.T. Light-Post), group 2, with glass fiber post(FRC Postec), and group 3, metal cast post and core. All teeth were fully covered with nonprecious metal crowns. Each specimen was embedded in an acrylic resin block and then secured in a universal load-testing machine. A compressive load was applied at a 130 degree angle to the long axis of the tooth until fractured, at a crosshead speed 20mm/min. The highest fracture loads were measured and recorded as the fracture strength of each specimen. Fracture areas were measured on the mid-buccal and mid-lingual point from the crown margins. One-way analysis of variance and Turkey test were used to determine the statistic significance of the different fracture loads and areas among the groups (p<0.05). Results: The mean fracture loads were $1391{\pm}$425N(group 1), $1458{\pm}476N$(group 2) and $1301{\pm}319N$(group 3). The fracture loads among the three groups had no statistically signifiant difference (p>.05). The mean fracture area of the fiber post was closer to the crown margin than that of the metal cast post and core(p<.05). The metal cast post showed unrestorable and catastrophic fracture patterns. Conclusion: Within the limitations of this study, fracture loads with any statistically significant difference were not recorded for endodontically treated teeth restored with two fiber posts and the metal cast post. But teeth restored with the fiber posts typically showed the fracture pattern close to the crown margin, which was almost restorable.

• Journal of Biomedical Engineering Research
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• v.19 no.5
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• pp.433-441
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• 1998

This study was performed to evaluate the effects of surface flaw on the fracture of all-ceramic materials. A feldspathic porce lain of VMK68, a cashable ceramic of IPS-Empress, and an alumina-glass composite of In-Ceram were used. Specimens were prepared as 12$\times$3$\times$1mm in dimensions, and a Vickers-produced indentation crack was made at the center of the tensile surface. Test specimens were immersed in dlstilled water and In oil, which were broken under a crosshead speed of 0.05 mm/min by 3-point bend test at 37$^{\circ}C$. The characteristic patterns of Vickers indentation and fracture surfaces were examined by an optical microscope and a scanning electron microscope. The fracture surfaces of the VMK68 and the IPS-Empress showed a median crack pattern at the fracture origin and indicated a tendency to cleavage hackle. The fracture surface of the alumina-glass composite, In-Ceram, showed a Palmqvist crack pattern at the fracture origin and indicated a tendency of toughening by the frictional Interlocking between the microstructurally rough fracture surfaces.

• Archives of Craniofacial Surgery
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• v.20 no.6
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• pp.376-381
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• 2019

Background: This study was conducted to determine the relationship between third molar (M3) and mandibular fracture. Methods: Patients with unilateral mandibular angle or condyle fractures between 2008 and 2018 were evaluated retrospectively. Medical records were reviewed regarding the location of fractures, and panoramic radiographs were reviewed to discern the presence and position of ipsilateral mandibular third molars (M3). We measured the bony area of the mandibular angle (area A) and the bony area occupied by the M3 (area B) to calculate the true mandibular angle bony area ratio (area A-B/area A×100). Results: The study consisted of 129 patients, of which 60 (46.5%) had angle fractures and 69 (53.5%) had condyle fractures. The risk of angle fracture was higher in the presence of M3 (odds ratio [OR], 2.2; p< 0.05) and the risk of condyle fracture was lower in the presence of M3 (OR, 0.45; p< 0.05), than in the absence of M3. The risk of angle fracture was higher in the presence of an impacted M3 (OR, 0.3; p< 0.001) and the risk of condyle fracture was lower in the presence of an impacted M3 (OR, 3.32; p< 0.001), than in the presence of a fully erupted M3. True mandibular angle bony area ratio was significantly lower in the angle fractures than in the condyle fractures (p= 0.003). Conclusion: Angle fractures had significantly lower true mandibular angle bony area ratios than condyle fractures. True mandibular angle bony area ratio, a simple and inexpensive method, could be an option to predict the mandibular fracture patterns.

• Journal of Clinical Otolaryngology Head and Neck Surgery
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• v.29 no.2
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• pp.198-203
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• 2018

Background and Objectives : Pediatric orbital blowout fractures occur in discreet patterns, in reference to the characteristic developmental anatomy of the facial skeleton at the time of injury. The purpose of this study was to investigate the clinical characteristics, ocular symptom, fracture type and postoperative results of orbital blowout fractures in the pediatric population. Material and Methods : A retrospective study was conducted from January 2009 to June 2015 in 116 patients with orbital floor fractures ; all less than 18 years old. Patients were divided into 3 groups by age : 0 to 6, 7 to 12, and 13 to 18 years of age. The cause of fracture, fracture site and type, preoperative and postoperative ocular symptoms, timing of surgery were reviewed from their records. Results : Medial wall fractures were the most common site in the 0 to 6 years old group, and floor fractures were the most common site in other age groups. However, floor fracture was the most common site of the need for surgery in all age groups. Trapdoor type of fractures occurred more frequently than open door type of fractures in all age groups. Preoperative symptoms did not differ among the 3 age groups. In case of need surgery, frequency of preoperative ocular symptoms increased with age. However, as age group was young, rate of residual postoperative ocular symptoms were increased. Conclusions : The younger patients are more to have trapdoor type fracture and residual postoperative ocular symptom. Earlier surgical intervention more needed for children with entrapment results.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2006.03a
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• pp.79-93
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• 2006

It is well known that acoustic emission (AE) is indicator of rock fracturing or damage as rock is brought to failure under the uniaxial compressive loads. In this paper, an experimental study on the source location of acoustic emission on the cylindrical specimens of granite under uniaxial compression test was made. The AE source location was made by measuring the six channel AE data. Comparing to this experiment, the numerical method is applied to model the initiation and propagation of fracture by AE using a numerical code, RFPA (Realistic Failure Process Analysis). This code incorporates the mesoscopic heterogeneity in Young's modulus and rock strength characteristic of rock masses. In the numerical models, values of Young's modulus and rock strength are realized according to a Weibull distribution in which the distribution parameters represent the level of heterogeneity of the medium. The results of the simulations show that RFPA can be used not only to produce acoustic emission similar to those measurements in our experiments, but also to predict fracturing patterns under uniaxial loading condition.

• Journal of the Korean Society of Safety
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• v.31 no.6
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• pp.6-11
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• 2016

CFRP composite laminates are widely used as structural materials for airplanes, automobile and aerospace vehicles because of their high strength and stiffness. This study aims to examine an effect of curvature on the penetration fracture characteristic of an orthotropic composite laminated shell. For the purpose, we manufactured orthotropic CFRP shell specimen with different curvatures, and conducted a penetration test using an air-gun. Those specimens were prepared to varied curvature radius(${\infty}$, 200mm, 150mm and 100mm)and were stacked to $[O^{\circ}{_3}/90^{\circ}{_3}]_s$. When the specimen is subjected to transverse impact by a steel sphere(${\Phi}10$), the velocity of steel sphere was measured both before and after impact by determining the time for it to pass two ball-screen sensors located a known distance apart. As the curvature increases, the absorption energy and the critical penetration energy increased linearly because the resistance to the bending moment. Patterns of cracks caused by the penetration of CFRP laminated shells included fiber breakage, lamina fracture, matrix crack interlaminar crack and intralaminar crack.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.27 no.5
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• pp.472-477
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• 2005

This study investigated the mandibular fractures that were treated at the Seoul National University Boramae Hospital in order to analyze the characteristics of mandibular fractures and the relationship between the causes and injury patterns. A total of 141 patients with mandibular fractures who were treated between 1996 and 2004 were analyzed retrospectively. The male to female ratio in the patient group was 5.13:1, and the mean age was 33.7 years. The most common etiologic factor was assaults (45.4%), and which was followed by activities associated with daily-life (40.4%) includeding falls, stumbling, collisions, and traffic accidents (11.3%). Single fracture sites were present in 75 patients (53.2%), two or more fracture sites were observed in other patients, and a total of 211 fracture sites were observed. The mandibular angle fractures (46.7%) was the most common in case of single fractures, and symphysis and angle fractures (45.4%) was most common in multiple fractures. Through out overall fracture sites, the most common fracture site was the symphysis (41.2%), followed by the angle (32.2%) and condyle (18.5%). Among assault and falls-related injuries, the common involving sites were the symphysis, and followed by the body and condyle. In case of traffic accidents, the symphysis fracture was the most common, and which was followed by the condyle and angle fractures. This study documented the characteristics of the mandibular fractures. The results demonstrate that preventive measures according to these characteristics will need to be implemented in order to minimize the risk of maxillofacial injuries.