• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.10a
• /
• pp.118-121
• /
• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• The Korean Journal of Ceramics
• /
• v.4 no.4
• /
• pp.356-362
• /
• 1998

Hertzian crack suppression phenomena and relatively high damage tolerance were investigated in hard/soft silicon nitride ($Si_3N_4$) bilayers. Coarse $\alpha}-Si_3N_4$ powder was wsed for the hard coating layer and fine $\alpha}-Si_3N_4$ powder was used for the soft substrate layer. The two layers were designed with a strong interface. Hertzian indentation was used to investigate contact fracture and damage tolerance property. Hertzian crack suppression has occurred with increasing applied load and decreasing coating thickness. The crack suppression contributed strength improvement, especially in the bilayers with thinner coatings. Ultimately, the combination of hard coating with soft but tough underlayer improved the damage tolerance of brittle $Si_3N_4$ ceramics.

• Journal of the Korean Ceramic Society
• /
• v.35 no.12
• /
• pp.1343-1350
• /
• 1998

A study is made of mechanical properties of unglazed matrix as a funtion of sintering temperature and crack patterns in layer structur pottery consisting of glaze and substrate and in matrix which is sintered at 120$0^{\circ}C$ and 130$0^{\circ}C$ respectively. The mechanical properties of matrix are increased due to density and vitrification to 130$0^{\circ}C$ The interface of glazed bilayer reveals the reactive intermediate layer. Herzian indentation testing is used to investigate the evolution of damage modes as a function of load. In the materials sintered at 120$0^{\circ}C$ quasi-plastic deformation is developed at the matrix and the cone-like cracks initiate at the glazing top surface and additionally upward-extending transverse cracks initiate at the internal in-just initiate at the glazing top surface which pass through the interface with increasing of indentation load. Finally the dominant damage mode shifts from substrate quasi-plasticity to coating fracture with increasing sintering temperature.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.3 no.5
• /
• pp.38-46
• /
• 1995

In this paper, an experimental study on the effects of the impact damage and the perforation characteristic of CFRP laminates with different fiber stacking orientation and ply number was done through an observation of interrelations between the impact energy vs. transmitted energy and the impact energy vs. absorbed energy per unit volume. The velocities of the ball before or after impact are measured by the high-speed camera. And when CFRP laminates are subjected to tranverse impact by a steel ball(${\phi}10$), the delamination shapes generated by impact damage are observed by using SAM (Scanning acoustic Microscope).

• Journal of Korean society of Dental Hygiene
• /
• v.11 no.1
• /
• pp.127-136
• /
• 2011

Objectives : The writer aimed to examine the dynamic aspect on damage and to be conducive to the swift cure according to right treatment to educate prevention of injury through surveying on the number of the damaged teeth given injury, tooth kind, type in damage, place and cause for being damaged, frequency by month and by time level, and location of the damaged tooth. Methods : Targeting 343 teeth of receiving injury in 201 patients who visited the department of pediatric dentistry, the department of preservation, and the oral and maxillofacial surgery in a dental hospital in Cheonan city from April 2007 to April 2009, by having the dental injury as the main reason, the following conclusions were obtained. Results : 1. Deciduous teeth were indicated to be the highest in imperfect luxation with 60.7%, and were indicated to be in order of crown fracture with 25.5%, root fracture with 12.4%, and perfect luxation with 1.4%. The permanent teeth were indicated to be the highest in crown with 58.1%, and were indicated to be in order of imperfect luxation with 27.3%, root fracture with 13.1%, and perfect luxation with 1.5%(p<0.001). 2. In case of deciduous teeth for a place with damage, the home was indicated to be the highest with 31.7%. The permanent teeth were indicated to be the highest(p<0.001) in the road and stairs with 40.4%. As to a cause for damage, both deciduous and permanent teeth were indicated to be the highest(p<0.001) in a cause for falling with 53.1% and 30.8%, respectively. 3. As for a treatment method, in case of deciduous teeth, the close observation was indicated to be the highest with 46.9%. In permanent teeth, the resin restoration was indicated to be the highest(p<0.001) with 22.2%. Dental injuries in deciduous teeth and permanent teeth are showing diverse aspects. Conclusions : It is important to arrange guidelines on cure of the damaged teeth by injury through continuing a dynamic research on these aspects. Also, the damage in deciduous teeth may have direct and indirect influence upon growth in successional permanent teeth. Thus, through careful treatment, the injury needs to be minimized. It is considered to be likely necessary for a right coping method when injury occurs, and above all, for enough prior education so that injury cannot occur.

• Journal of Korean Foot and Ankle Society
• /
• v.1 no.1
• /
• pp.30-37
• /
• 1997

Pilon fracture is an intraarticular fracture of distal tibia. It is high energy injury with significantly associated soft tissue damage, bone comminution, and articular surface disruption. Until recently, this treatment has followed the AO principles, Because the risk of complications outweighs potential benefits, the principle of a Pilon fracture treatment are changing. Newer techniques using articulated external fixation minimize disturbance of the soft tissue envelope and have decreased these complications. Series of 5 patients with Pilon fracture were treated by articulated external fixator and followed up more than 12 monthes at the Department of orthopaedic surgery, Kang Dong Sacred Heart Hospital, College of medicine, Hallym University. The results were as follows: 1. The type of fracture were type C2(3 cases),type C3(2 cases) according to AO-$M{\ddot{u}}ller$ classification. 2. The clinical results according to functional criteria by Mast and Teipner were good in 4 cases and poor in 1 case, which is an old fracture. 3. Techniques utilizing articulated external fixator were associated with satisfactory results and appeared to significantly decrease the incidence of soft tissue complication, post-traumatic arthritis, osteoporosis, and fibrosis of ankle joint.

• Geomechanics and Engineering
• /
• v.7 no.3
• /
• pp.233-246
• /
• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.21 no.3
• /
• pp.251-260
• /
• 2001

Damage Profess of CFRP laminates under monotonic tensile test was characterized by the correlation between Acoustic Emission(AE) and Ultrasonic Test(UT). The amplitude distribution of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pullout and fiber fracture as load is increased. In addtion, the characteristics of ultrasonic amplitude attenuation are useful lot analysis of the different type of fracture mechanism. Different orientation of carbon fiber reinforced plastic specimens were used to investigate the AE amplitude range and ultrasonic amplitude attenuation. Finally, loading-unloading tests were carried out to check Felicity effect. During the tests, ultrasonic amplitude attenuation was investigated at the same time and compared with AE parameters. The result showed that two parameters of both AE and UT could be effectively used for analysis of fracture mechanism in CFRP laminates.

• The Journal of Advanced Prosthodontics
• /
• v.12 no.4
• /
• pp.218-224
• /
• 2020

PURPOSE. The objectives of this study were to evaluate the fracture strength and fracture patterns of provisional crowns fabricated from different materials and techniques after receiving stress from a simulated oral condition. MATERIALS AND METHODS. A monomethacrylate-based resin (Unifast Trad) and a bis-acryl-based (Protemp 4) resin were used to fabricate provisional crowns using conventional direct technique. A milled monomethacrylate resin (Brylic Solid) and a 3D-printed bis-acrylate resin (Freeprint Temp) were chosen to fabricate provisional crowns using the CAD/CAM process. All cemented provisional crowns (n=10/group) were subjected to thermal cycling (5,000 cycles at 5°-55℃) and cyclic occlusal load (100 N at 4 Hz for 100,000 cycles). Maximum force at fracture was tested using a universal testing machine. RESULTS. Maximum force at fracture (mean ± SD, N) of each group was 657.87 ± 82.84 for Unifast Trad, 1125.94 ± 168.07 for Protemp4, 953.60 ± 58.88 for Brylic Solid, and 1004.19 ± 122.18 for Freeprint Temp. One-way ANOVA with Tamhane post hoc test showed that the fracture strength of Unifast Trad was statistically significantly lower than others (P<.01). No statistically significant difference was noted among other groups. For failure pattern analysis, Unifast Trad and Brylic Solid showed less damage than Protemp 4 and Freeprint Temp groups. CONCLUSION. Provisional crowns fabricated using the CAD/CAM process and the conventionally fabricated bis-acryl resins exhibited significant higher fracture strength compared to conventionally fabricated monomethacrylate resins after the aging regimen. Therefore, CAD/CAM milling and 3D printing of provisional restorations may be good alternatives for long term provisionalization.

• Geomechanics and Engineering
• /
• v.9 no.5
• /
• pp.645-667
• /
• 2015

Single treatment and staged treatments in vertical wells are widely applied in sandstone and mudstone thin interbedded (SMTI) reservoir to stimulate the reservoir. The keys and difficulties of stimulating this category of formations are to avoid hydraulic fracture propagating through the interface between shale and sand as well as control the fracture height. In this paper, the cohesive zone method was utilized to build the 3-dimensional fracture dynamic propagation model in shale and sand interbedded formation based on the cohesive damage element. Staged treatments and single treatment were simulated by single fracture propagation model and double fractures propagation model respectively. Study on the changes of fracture vicinity stress field during propagation is to compare and analyze the parameters which influence the interfacial induced stresses between two different fracturing methods. As a result, we can prejudge how difficult it is that the fracture propagates along its height direction. The induced stress increases as the pumping rate increasing and it changes as a parabolic function of the fluid viscosity. The optimized pump rate is $4.8m^3/min$ and fluid viscosity is $0.1Pa{\cdot}s$ to avoid the over extending of hydraulic fracture in height direction. The simulation outcomes were applied in the field to optimize the treatment parameters and the staged treatments was suggested to get a better production than single treatment.