• Restorative Dentistry and Endodontics
• /
• 제24권4호
• /
• pp.604-613
• /
• 1999

This study was performed to evaluate the effect of resin and filler type on the fracture toughness of light-activated composites. Experimental composites were prepared using urethane tetramethacrylate(UTMA) and bisphenol glycidylmethacrylate(Bis-GMA) monomers and five different types of silica fillers. Fracture toughness was measured by a single edge V-notched beam(SEVNB) method, which was discussed from ASTM E399-78. Rectangular bars of $2.5{\times}5{\times}26mm$ were prepared with experimental composites and a notch about 2.25mm deep was carved at the center of the long axis of the specimen using a dental diamond disk driven by a dental micro engine. The flexural test was carried out at a crosshead speed of 0.05mm/min and fracture surfaces were observed under scanning electron microscope. The results obtained were summarized as follows: 1. The fracture toughness values of UTMA-based composites were relatively higher than those of Bis-GMA-based composites. 2. The highest fracture toughness value was observed in the UTMA-based composite containing the $1.5{\mu}m$-spherical fillers. 3 Aging in the distilled water at $37^{\circ}C$ for 10 days showed the increase of fracture toughness, which was severer in the Bis-GMA-based composites than those of UTMA-based composites. 4. The AE amplitude occurring during the fracture toughness tests was the highest at the point of macroscopic fracture.

• Geomechanics and Engineering
• /
• 제6권2호
• /
• pp.153-172
• /
• 2014

In order to investigate the effect of different perforation angles (the angle between the perforation direction and the maximum horizontal principal stress) on the fracture initiation and propagation during hydraulic fracturing of highly deviated well in oil & gas saturated formation, laboratory experiments of the hydraulic fracturing had been carried out on the basis of non-dimensional similar criteria by using 400^3 $mm^3$ cement cubes. A plane fracture can be produced when the perforations are placed in the direction of the maximum horizontal principal stress. When the perforation angle is $45^{\circ}$, the fractures firstly initiate from the perforations at the upper side of the wellbore, and then turn to the maximum horizontal principal stress direction. When the well deviation angle and perforation angle are both between $45^{\circ}$ and $90^{\circ}$, the fractures hardly initiate from the perforations at the lower side of the wellbore. Well azimuth (the angle between the wellbore axis and the maximum horizontal principal stress) has a little influence on the fracture geometries; however it mainly increases the fracture roughness, fracture continuity and the number of secondary fractures, and also increases the fracture initiation and propagation pressure. Oriented perforating technology should be applied in highly deviated well to obtain a single plane fracture. If the well deviation angle is smaller, the fractures may link up.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 2005년도 춘계학술발표회
• /
• pp.199-200
• /
• 2005

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2001년도 학술발표회 논문집(I)
• /
• pp.465-470
• /
• 2001

No Abstract (See Full-text)

• 대한기계학회논문집A
• /
• 제21권3호
• /
• pp.519-527
• /
• 1997

AISI 316 steel has been used extensively for heater and boiler tube of the structural plants such as power, chemical and petroleum plants under severe operating conditions. Usually, material degradation due to microcrack or precipitation of carbides and segregation of impurity elements, is occured by damage accumulated for long-term service at high temperature in this material. In this study, the effect of aging time on fracture toughness was investigated to evaluate the measurement of material degradation. The elastic-plastic fracture toughness behaviour of AISI 316 steel pipe aged at $550^{\circ}C$for 1h-10000h (the aged material) was characterized using the single specimen J-R curve technique and eletric potential drop method at normal loading rate(load-line displacement speed of 0.2mm/min) in room temperature and air environment. The fracture toughness data from above experiments is compared with the $J_{in}$ obtained from predicted values of crack initiation point using potential drop method.

• Steel and Composite Structures
• /
• 제22권2호
• /
• pp.399-409
• /
• 2016

The fracture propagation mechanism and fractured rock mass failure mechanism were important research in geotechnical engineering field. Many failures and instability in geotechnical engineering were related on fractures propagation, coalescence and interaction in rock mass under the external force. Most of the current research were limited to two-dimensional for the brittleness and transparency of three-dimensional fracture materials couldn't meet the requirements of the experiment. New materials with good transparent and brittleness were developed by authors. The making method of multi fracture specimens were established and made molds that could be reused. The tension-compression ratio of the material reached above 1/6 in normal temperature. Uniaxial and biaxial loading tests of single and double fracture specimens were carried out. Four new fractures were not found in the experiment of two-dimensional fractures such as the fin shaped crack, wrapping wing crack and petal crack and anti-wing crack. The relationship between stress and strain of the specimens were studied. The specimens with the load had experienced four stages of deformation and the process of the fracture propagation was clearly seen in each stage. The expansion characteristics of the fractured specimens were more obvious than the previous research.

• Journal of the Korean Wood Science and Technology
• /
• 제17권4호
• /
• pp.70-76
• /
• 1989

The fracture toughness of two species, Pinus rigida MILL and Pinus koraiensis S. et Z. grown in Korea, was investigated by means of single edge notch beam specimen for the six principal systems of crack propagation in wood. The values of the fracture toughness for the LR and the LT systems ($K_{IC}$LR and $K_{IC}$LT) were found to be similar to each other and about 8 times greater than those for the other systems ($K_{IC}$RL, $K_{IC}$TL and $K_{IC}$TR) in both species. The results indicate that the characteristics of fracture toughness in three principal directions of wood (L, R, T direction) are quite different from those of bending strength for the responsible direction. To predict $K_{IC}$ value based on the variation of specific gravity, the experimental values of $K_{IC}$LT and $K_{IC}$TL were compared to the predicted values by published relationship between $K_{IC}$ and specific gravity. However, there were 10 to 25% differences between the former and the latter.

• Carbon letters
• /
• 제7권1호
• /
• pp.19-26
• /
• 2006

Three point bending tests of single edge notched beam (SENB) specimens were carried out to evaluate the fracture behavior of the fine-grain isotropic nuclear grade graphite, IG-11. To measure the crack initiation point and the subsequent crack growth, the direct current potential drop (DCPD) method and a traveling microscope were used. The effects of test variables like initial crack length, specimen thickness, notch type and loading rate on the measured fracture toughness, $K_Q$, were investigated. Based on the test results, the ranges of the test variables to measure the reliable fracture toughness value were proposed. During the crack growth, the rising R-curve behavior was observed in IG-11 graphite when the superficial crack length measured on the specimen surface was used. The increase of crack growth resistance was discussed in terms of crack bridging, crack meandering, crack branching, microcracking and crack deflection, which increase the surface energy and friction force.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제46권6호
• /
• pp.393-402
• /
• 2020

Objectives: Here, we present cases of mandibular fracture that were managed with the cortical lag screw fixation technique (CLSFT) in order to critically evaluate technique indications and limitations of application at various fracture sites. Materials and Methods: This was a retrospective cohort study. The study sample was composed of patients suffering from mandibular fractures that were treated by the CLSFT. The outcome variables were fracture type, duration of surgery, number of screws, and pattern of application. Other study categories included patient demographics and causes of injury. Chi-square tests were used to assess descriptive and inferential statistical differences, and the P-value was set at 0.05. Results: Thirty-three patients were included in the study sample, with a mean age of 30.9±11.5 years and a male predominance of 81.8%. The technique was applied more frequently in the anterior mandibular region (51.5%) than in other sites. Double CLSFT screws were required at the symphysis and parasymphysis, while single screws were used for body and angle regions. No intraoperative and postoperative variables were significantly different except for surgical duration, which was significantly different between the sites studied (P=0.035). Conclusion: We found that CLSFT is a rapid, cost-effective technique for the fixation of mandibular fractures yielding good treatment results and very limited complications. However, this technique is sensitive and requires surgical expertise to be applied to mandibular fractures that have specialized characteristics.

• 한국구조물진단유지관리공학회 논문집
• /
• 제21권5호
• /
• pp.1-11
• /
• 2017

This study focused on the ultimate behaviors(ultimate strength and fracture mode ) of single shear bolted connection with austenitic sainless steel(STS201) and curling effect on the ultimate strength using finite element analysis based on test results. Main variables are end distance in the parallel direction to loading and edge distance in the perpendicular direction to loading. The validation of finite element analysis procedures was verified through the comparisons of ultimate strength, fracture mode and curling(out-of-plane deformation) occurrence between test results and numerical predictions. Curling was observed in both test and analysis results and it reduced the ultimate strength of single- shear bolted connections with relatively long end distances. Strength reduction ratios caused by curling were estimated quantitatively by maximum 19%, 32%, respectively for specimens with edge distance, 48 mm and 60 mm compared with strengths of uncurled connections with restrained out-of-plane deformation. Finally, analysis strengths were compared with current design strengths and it is found that design block shear equations did not provide the accurate predictions for bolted connections with strength reduction by curling.