• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.643-648
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• 2010

Waterjet is a very useful technology for rock excavation because of low level noise and vibration during breaking rocks. To accurately predict the volume and shape excavated by the waterjet, it is important to understand waterjet fracture mechanisms. There have been various theoretical assumptions and approaches in the literature. In this study, waterjet mechanisms are classified into three standards: a mechanism scale, theoretical assumption for a target material, and jet phase. In addition, through a waterjet experimental study for weathered and intact granitic rocks, a fracture shape is observed and analyzed on comparison with the previous mechanisms. As a result, best waterjet mechanisms are selected to explain the fracture pattern of the granitic rocks.

• Structural Engineering and Mechanics
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• v.11 no.6
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• pp.591-604
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• 2001

In this paper, a finite element with embedded displacement discontinuity which eliminates the need for remeshing of elements in the discrete crack approach is applied for the progressive fracture analysis of concrete structures. A finite element formulation is implemented with the extension of the principle of virtual work to a continuum which contains internal displacement discontinuity. By introducing a discontinuous displacement shape function into the finite element formulation, the displacement discontinuity is obtained within an element. By applying either a nonlinear or an idealized linear softening curve representing the fracture process zone (FPZ) of concrete as a constitutive equation to the displacement discontinuity, progressive fracture analysis of concrete structures is performed. In this analysis, localized progressive fracture simultaneous with crack closure in concrete structures under mixed mode loading is simulated by adopting the unloading path in the softening curve. Several examples demonstrate the capability of the analytical technique for the progressive fracture analysis of concrete structures.

• Advances in concrete construction
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• v.2 no.1
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• pp.13-27
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• 2014

The principal objective of this study is to deepen the characterization studies already led on sand concretes in previous works. Indeed, it consists in studying the effect of the sand type on the main properties of sand concrete: fracture and mechanical properties. We particularly insist on the determination of the fracture characteristics of this material which apparently have not been studied. To carry out this study, four different types of sand have been used: dune sand (DS), river sand (RS), crushed sand (CS) and river-dune sand (RDS). These sands differ in mineralogical nature, grain shape, angularity, particle size, proportion of fine elements, etc. The obtained results show that the particle size distribution of sand has marked its influence in all the studied properties of sand concrete since the sand having the highest diameter and the best particle size distribution has given the best fracture and mechanical properties. The grain shape, the angularity and the nature of sand have also marked their influence: thanks to its angularity and its limestone nature, crushed sand yielded good results compared to river and dune sands which are characterized by rounded shape and siliceous nature. Finally, it should further be noted that the sand concrete presents values of fracture and mechanical properties slightly lower than those of ordinary concrete. Compared to mortar, although the mechanical strength is lower, the fracture parameters are almost comparable. In all cases, the sand grains are debonded from the paste cement during the fracture which means that the crack goes through the paste-aggregate interface.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.2
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• pp.46-53
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• 1988

Effect of Notch Shape and Hardness Ratio on Characteristics of Impact Fracture in Dual Phase Steels. In this study, it is investigated the effect of notch shape and hardness ratio on the characteristics of impact fracture in dual phase steels. The impact test was carried out at the temperature range from -40.deg. C to room temperature with Instrumented Charpy Impact Tester. The main results obtained are as follows; 1, The maximum impact bending strength (.sigma.$_{max}$) increases with the tensile strength. Also, the impact energy depends on .sigma.$_{max}$. 2, In room temperature, the impact energy depends on crack-initiation energy (E$_{i}$) in case of the high hardness ratio (R=3.4), whereas depends on crack-propagation energy (E$_{p}$) in case of the low hardness ratio (R=1.8) and the dependence of crack-initiation energy of the impact characteristics decreases with increasing test temperature. These phenomena are result from the difficulty of cleavage facet formation.ion.ion.

• The Journal of Advanced Prosthodontics
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• v.9 no.1
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• pp.22-30
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• 2017

PURPOSE. The aim of this study was to investigate the effect of reinforcing materials on the fracture resistances of glass fiber mesh- and Cr-Co metal mesh-reinforced maxillary complete dentures under fatigue loading. MATERIALS AND METHODS. Glass fiber mesh- and Cr-Co mesh-reinforced maxillary complete dentures were fabricated using silicone molds and acrylic resin. A control group was prepared with no reinforcement (n = 15 per group). After fatigue loading was applied using a chewing simulator, fracture resistance was measured by a universal testing machine. The fracture patterns were analyzed and the fractured surfaces were observed by scanning electron microscopy. RESULTS. After cyclic loading, none of the dentures showed cracks or fractures. During fracture resistance testing, all unreinforced dentures experienced complete fracture. The mesh-reinforced dentures primarily showed posterior framework fracture. Deformation of the all-metal framework caused the metal mesh-reinforced denture to exhibit the highest fracture resistance, followed by the glass fiber mesh-reinforced denture (P<.05) and the control group (P<.05). The glass fiber mesh-reinforced denture primarily maintained its original shape with unbroken fibers. River line pattern of the control group, dimples and interdendritic fractures of the metal mesh group, and radial fracture lines of the glass fiber group were observed on the fractured surfaces. CONCLUSION. The glass fiber mesh-reinforced denture exhibits a fracture resistance higher than that of the unreinforced denture, but lower than that of the metal mesh-reinforced denture because of the deformation of the metal mesh. The glass fiber mesh-reinforced denture maintains its shape even after fracture, indicating the possibility of easier repair.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.25 no.2
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• pp.471-482
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• 1995

Bony remodeling pattern of condyle fractures in children are different from in adult for growing of condyle, also might affect treatment and prognosis of the condyle fracture. Subjects of this clinical and radiologic study were 26 temporomandibular joints diagnosed as condyle fracture in 23 patients under 15 years old age. They were treated with conservative method at Dental Hospital of Yonsei University from Jan., 1986 to Oct., 1994. Bony remodeling related with fracture pattern was evaluated. The results obtained are as follows: 1. The ratio of male to female in patients with condyle fracture was 1 : 0.9 and the difference of sex ratio was not noted. Comparing with preschool-age group and school-age group, age frequency was higher in preschool-age group(83％). 2. Fallen down(54％) was the most frequent cause of condyle fractures. Traffic accident and slip down were followed. 3. The most common clinical sign of condyle fractures was tenderness to paipation09 cases). Mouth opening limitation07 cases), swelling(7 cases), malocclusion(3 cases) were next in order. 4. According to sites of condyle fractures, unilateral fractures were in 20 patients and bilateral fractures in 3 patients, therefore total 23 patients-26 cases of condyle fracture were observed. According to fracture distribution, condyle fractures were in 10 patients(44％). Condyle fractures with symphysis fracture(9 patients, 39％), condyle fractures with ascending ramus fracture(2 patients, 9％), condyle fracture with mandibular body fracture(1 patient, 4％), and condyle fractures with mandibular angle fracture(1 patient, 4％) were followed. 5. In displacement pattern of fractured fragment of mandibular condyle, dispiacement(17 cases, 66％) was most common. Dislocation(5 cases, 19％) and deviation (4 cases, 15％) were next in order. 6. During the observation period of fractured condyles, remodeling patterns of fracture sites related with articular fossa were observed with usual condylar shape in 23 cases and with prominently different shape in 3 cases.

• Archives of Craniofacial Surgery
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• v.20 no.6
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• pp.347-353
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• 2019

Most orbital surgeons believe that it's difficult to restore the primary orbital wall to its previous position and that the orbital wall is so thin that cannot be firmly its primary position. Therefore, orbital wall fractures generally have been reconstructed by replacing the bony defect with a synthetic implant. Although synthetic implants have sufficient strength to maintain their shape and position in the orbital cavity, replacement surgery has some drawbacks due to the residual permanent implants. In previous studies, the author has reported an orbital wall restoring technique in which the primary orbital wall fragment was restored to its prior position through a combination of the transorbital and transantral approaches. Simple straight and curved elevators were introduced transnasally to restore the orbital wall and to maintain temporary extraorbital support in the maxillary and ethmoid sinus. A transconjunctival approach provided sufficient space for implant insertion, while the transnasal approach enabled restoration of the herniated soft tissue back into the orbit. Fracture defect was reduced by restoring the primary orbital wall fragment to its primary position, making it possible to use relatively small size implant, furthermore, extraorbital support from both sinuses decreased the incidence of implant displacement. The author could recreate a natural shape of the orbit with the patient's own orbital bone fragments with this dual approach and effectively restored the orbital volume and shape. This procedure has the advantages for retrieving the orbital contents and restoring the primary orbital wall to its prior position.

• Journal of Technologic Dentistry
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• v.36 no.4
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• pp.231-237
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• 2014

Purpose: This study was performed fracture strength test by conducted change of abutment and coping shape for suggesting monolithic all ceramic crown which has thin thickness and superior strength of the occlusal surface. Methods: The specimens on the four kinds abutment was made according to thickness of occlusal surface and angle of axis surface. And All ceramic coping specimens of 6 different kinds was made by the CAD/CAM Method. Compression strength test using the UTM and the verification of compression-stress situation using the 3D finite element method were conducted under optimum conditions. Results: 516C specimen was showed the strongest compression-fracture strength, followed by 516FR, 516F45, specimens. Did not show significant differences between 516FR and 516F45. 516C of the universal testing machine the specimen's surface that are within the vertical load is small, finite element method of a uniformly distributed load, so the value received suggests otherwise. Conclusion: In conclusion, abutments of monolithic ziconia ceramic when having a same thickness of the occlusal, as the angle of occlusal edge is small, the stress is well dispersed and it can endure well in the fracture.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.111-116
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• 2001

A practical scheme to reduce failure of the PCB(Printed Circuit Board) of a monitor is introduced using deformed mode shape under mechanical shock. When the monitor is given critical shock loads, cracks are commonly initiated at the tip of a hole on the PCB. Accordingly, a deformed mode shape of the PCB is obtained using a FEM code to define a weak point on the PCB under mechanical shock, and then the position and direction of the hole is determined to prevent the failure at the critical mode shape. Also, the stress intensity factor around the weak point on the PCB is calculated to check the possibility of fracture by normal tensile stress. In conclusion, present research is useful to assist the practical design of components-layout on the PCB.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.98-105
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• 2016

In this study, projectiles with 2 kinds of nose shape: spherical and flat were impacted into normal concrete and fiber reinforced concrete panels. The fracture depth and form, crater diameter, tensile strain at rear face were evaluated. It was confirmed that smaller projectile nose areas resulted in deeper penetrations associated with concentrated impact forces and small front-face crater diameters in impact test. Conversely, larger projectile nose areas resulted in shallower penetrations and larger front-face fracture diameters. Similar front-face failure and strain distribution relationships based on the projectile nose shape were observed for normal and fiber-reinforced concrete although the rear-face tensile strain and scabbing were significantly reduced by the fiber reinforcement. In addition, a direct relationship was confirmed between the penetration depth based on the projectile nose shape and the tensile strain on the rear face. Thus the impact strain behavior is required to predict the scabbing behavior with penetration depth.