• Advanced Composite Materials
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• 제16권2호
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• pp.83-94
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• 2007

Woven sisal textile fiber reinforced composites were used to evaluate fracture toughness, tensile and three-point bending. The water absorption testing of all specimens was repeated five times in this study. All specimens were immersed in pure water during 9 days at room temperature, and dried in 1 day at $50^{\circ}C$. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surfaces were taken to study the failure mechanism and fiber/matrix interfacial adhesion. It is shown that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples showed poor mechanical properties, such as lower values of maximum strength and extreme elongation. The $K_{IC}$ values demonstrated a decrease in inclination with increasing cyclic times of wetting and drying for the epoxy and vinyl-ester.

• Restorative Dentistry and Endodontics
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• 제20권2호
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• pp.856-868
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• 1995

The effect of collagen dissolution in acid conditioned dentin layer on resin - dentin adhesion was investigated. 160 freshly extracted human molars were divided into 4 groups randomly and dentin surfaces were exposed. 40 exposed dentin surfaces were not acid conditioned and each 10 of them were applied with bonding agents within dentin bonding systems of All Bond 2, Scotchbond Multipurpose, Clearfil Photobond and Superbond D - Liner respectively. Each 10 of another 40 exposed dentin surfaces were acid conditioned by the acid within the above four bonding systems respectively and applied with corresponding bonding systems. After acid conditioning of the other 40 exposed dentin surfaces as above, they were treated with 5% NaOCl for 2 minutes, and each 10 of them were applied with the above four dentin bonding systems respectively. The remaining 40 dentin surfaces were acid conditioned and treated with 10% NaOCl for 2 minutes, and each 10 of them were applied with corresponding bonding agents as the above. After the procedures were finished, composite resin (Z -100, 3M Dent. Prod., USA) were applied on the dentin surfaces and light cured. Shear bond strength values were measured. Surface changes of fractured dentin specimens were observed using SEM (Hitachi S-2350, Japan). The following results were obtained. 1. In all of dentin bonding systems, shear bond strengths of non - conditioned specimens were significantly lower than those of acid conditioned specimens (P<0.05). 2. A statistically significant difference of bond strengths did not exist between acid conditioned specimens and 5% NaGCI retreated specimens applied with All Bond 2, Scotchbond Multipurpose and Clearfil Photobond (P>0.05). However, strength values of 5% NaOCl retreated specimens applied with Superbond D - Liner were lower than those of acid conditioned specimens (P<0.05). 3. In all the applied dentin bonding systems except Clearfil Photobond, bond strengths of 10% NaOCl retreated specimens were lower than those of acid conditioned and 5% NaOCl retreated specimens (P<0.05). 4. The resin - dentin hybrid layer of 4 - $5{\mu}m$ thickness was formed in the acid conditioned specimens applied with All Bond 2, Scotchbond Multipurpose and Superbond D-Liner. 5. The resin - dentin hybrid layer of 3 - $4{\mu}m$ thickness was still formed in the 5% NaOCl retreated specimens applied with All Bond 2 and Scotchbond Multipurpose. In addition, this layer was not completely removed after the retreatment with 10% NaOCl. Above results indicate that the dissolution of collagen in acid conditioned dentin layer by NaOCl solution can not be achieved completely and the collagens contribute to the resin - dentin adhesion considerably.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.481-495
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• 2015

Many hydropower stations in southwest China are located in regions of brittle rock mass with high geo-stresses. Under these conditions deep fractured zones often occur in the sidewalls of the underground caverns of a power station. The theory and methods of fracture and damage mechanics are therefore adopted to study the phenomena. First a flexibility matrix is developed to describe initial geometric imperfections of a jointed rock mass. This model takes into account the area and orientation of the fractured surfaces of multiple joint sets, as well as spacing and density of joints. Using the assumption of the equivalent strain principle, a damage constitutive model is established based on the brittle fracture criterion. In addition the theory of fracture mechanics is applied to analyze the occurrence of secondary cracks during a cavern excavation. The failure criterion, for rock bridge coalescence and the damage evolution equation, has been derived and a new sub-program integrated into the FLAC-3D software. The model has then been applied to the stability analysis of an underground cavern group of a hydropower station in Sichuan province, China. The results of this method are compared with those obtained by using a conventional elasto-plastic model and splitting depth calculated by the splitting failure criterion proposed in a previous study. The results are also compared with the depth of the relaxation and fracture zone in the surrounding rock measured by field monitoring. The distribution of the splitting zone obtained both by the proposed model and by the field monitoring measurements are consistent to the validity of the theory developed herein.

• Journal of Welding and Joining
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• 제32권3호
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• pp.60-67
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• 2014

The ability of electronic packages and assemblies to resist solder joint failure is becoming a growing concern. This paper reports on a study of high speed shear energy of Sn-4.0wt%Ag-0.5wt%Cu (SAC405) solder with different electroless Ni-P thickness, with $HNO_3$ vapor's status, and with various pre-conditions. A high speed shear testing of solder joints was conducted to find a relationship between the thickness of Ni-P deposit and the brittle fracture in electroless Ni-P deposit/SAC405 solder interconnection. A focused ion beam (FIB) was used to polish the cross sections to reveal details of the microstructure of the fractured pad surface with and without $HNO_3$ vapor treatment. A scanning electron microscopy (SEM) and an energy dispersive x-ray analysis (EDS) confirmed that there were three intermetallic compound (IMC) layers at the SAC405 solder joint interface: $(Ni,Cu)_3Sn_4$ layer, $(Ni,Cu)_2SnP$ layer, and $(Ni,Sn)_3P$ layer. The high speed shear energy of SAC405 solder joint with $3{\mu}m$ Ni-P deposit was found to be lower in pre-condition level#2, compared to that of $6{\mu}m$ Ni-P deposit. Results of focused ion beam and energy dispersive x-ray analysis of the fractured pad surfaces support the suggestion that the brittle fracture of $3{\mu}m$ Ni-P deposit is the result of Ni corrosion in the pre-condition level#2 and the $HNO_3$ vapor treatment.

• 대한치과보철학회지
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• 제29권2호
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• pp.195-209
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• 1991

When the porcelain fused to metal restorations were fractured at the metal interface, various techniques and materials for intraoral porcelain repair have been suggested. The purpose of this study was to investigate the effect of metal surface treatment method and water storage on the shear bond strength of four porcelain repair systems. : Clearfil(Kuraray), All-bond(Bisco), Superbond C & B(Sun Medical), Panavia OP(Kuraray). After the metal surfaces of the specimens were sandblasted by aluminum oxide or roughened by diamond point, they were stored in double deionized water(24 Hr., $37^{\circ}C$) and thermocycling was performed(24 Hr., 1024 cycles), and again half of specimes were stored in water bath(2 Months, $37^{\circ}C$). Mean shear bond strength and mode of failure were recorded. The results of this study were obtained as follows : 1. Differences were observed between the sandblasted and diamond - treated specimens in Clearfil, All-bond, and Superbond. No statistically significant differences were observed in Panavia. 2. The 2-month storage time significantly affected the bond strength of All-bond and Superbond. No statistically significant differences were observed in Clearfil and Panavia. 3. The failures were observed at the interface between opaque resin and the metal in Clearfil and All-bond. 4. The failures were observed at the interface between opaque resin and veneered resin in Panavia. The failures were observed at the interface between opaque resin and veneered resin in Superbond, but 40% of them were fractured at the interface between the metal and opaque resin after 2-month storage time.

• 대한치과보철학회지
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• 제38권6호
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• pp.782-790
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• 2000

The mainly used polymeric material for the denture is PMMA because of its cost and easiness to handle. So it was widely used material among dentists for past decades. But the acrylic-based denture materials have several common weak points such as shrinkage after curing and lack of strength. In order to solve these problems, we adapted one of hybrid system using acrylic polymer and vinyloligosilsesquioxane(POSS). POSS, which is a well known expandable monomer during polymerization process, may eventually suppress volumetric shrinkage. And the hybrid system makes it possible for the polymer to be stable in various severe conditions. Eight different kinds of samples were designed and synthesized. Each samples were characterized with dynamic mechanical analyser(DMA) to confirm their thermodynamic properties, fractured to analyze the cross-sectional morphology of the samples. And elongation, flexural and impact tests were also executed to evaluate the mechanical properties of the samples. From the results, hybrid composites had well defined crosslinked network structure compared to the widely used denture materials, and the mechanical strength improved without changing any surface condition as increment with POSS ratio in hybrid system. Fractured morphology showed homogeneous surfaces in spite of mutli component system, therefore we can conclude that the adoption of the POSS brought the reinforcement of the denture resin.

• Restorative Dentistry and Endodontics
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• 제29권3호
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• pp.267-272
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• 2004

The purpose of this in vitro study was to evaluate the effect of surface defects and cross-sectional configuration of NiTi rotary files on the fatigue life under cyclic loading. Three NiTi rotary files ($K3^{TM},{\;}ProFile^{\circledR},{\;}and{\;}HERO{\;}642^{\circledR}$) with ＃30/.04 taper were evaluated. Each rotary file was divided into 2 subgroups : control (no surface defects) and experimental group (artificial surface defects), A total of six groups of each 10 were tested. The NiTi rotary files were rotated at 300rpm using the apparatus which simulated curved canal (40 degree of curvature) until they fracture. The number of cycles to fracture was calculated and the fractured surfaces were observed with a scanning electron microscope. The data were analyzed statistically. The results showed that experimental groups with surface defects had lower number of cycles to fracture than control group but there was only a statistical significance between control and experimental group in the $K3^{TM}$ (p<0.05), There was no strong correlation between the cross-sectional configuration area and fracture resistance under experimental conditions. Several of fractured files demonstrated characteristic patterns of brittle fracture consistent with the propagation of pre-existing cracks. This data indicate that surface defects of NiTi rotary files may significantly decrease fatigue life and it may be one possible factor for early fracture of NiTi rotary files in clinical practice.

• 대한치과보철학회지
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• 제52권2호
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• pp.67-73
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• 2014

연구 목적: 본 연구의 목적은 주조, 3-D printing laser sintered 및CAD/CAM technology를 이용한 milling 방법으로 제작된 치과용 코발트-크롬 합금의 기계적 물성을 비교하고 파절 단면의 미세 구조를 살펴보는 데 있다. 이를 통해 새롭게 소개된 제작 기법 - 3D-printing laser sintered - 이 치과용 합금 제작으로 적합한 지 알아보고자 한다. 연구 재료 및 방법: 36개의 flat disc 모양의 시편을 제작하여 제작 방법에 따라 세 집단으로 나누었다; 주조 방식으로 제작한 12개, laser sintering 방법으로 12개, CAD/CAM milling 방법으로 12개의 시편을 제작하여 표면 경도 시험을 시행하였다. 또한 각 집단 별로 12개의 dumbbell 모양의 시편을 제작하여 인장 강도 시험을 시행하였다. 통계량이 비모 수적 통계 분포를 보였으므로 Kruskal-Wallis 검정을 이용하여 각 실험군의 인장 강도 시험 결과를 비교했으며, 통계적 유의 수준은P=.05로 설정하여 Mann-Whitney 및 Bonferroni 사후 검정을 시행하였다. 전자 주사 현미경을 사용하여 파절 단면의 미세 구조를 관찰하였다. 결과: Vickers hardness test에서 세 집단간에 모두 유의한 차이가 있었고, 주조 방식으로 제작된 실험군에서 가장 큰 표면 경도(455.88 Hv)가, CAD/CAM milling으로 제작된 실험군에서 가장 낮은 표면 경도(243.40 Hv)를 나타냈다. 최대 인장 강도, 0.2% 항복강도, elongation 및 elastic modulus에서 세 집단간에 모두 유의한 차이가 나타났으며, CAD/CAM milling으로 제작한 실험군에서 가장 높은 최대 인장 강도(1442.94 MPa)가, laser sintered 실험군에서 가장 큰 0.2% 항복 강도(1136.15 MPa)가 나타났다. 파절 단면의 전자 주사 현미경 관찰 결과, 주조 시편에서는 독특한 성긴 모양과 전형적인 주조 다공성 구조가 관찰되었고, laser sintered 시편에서는 편평한 면을 동반한 거친 결정 구조가, 그리고 milled 시편에서는 균일하고 규칙적인 치밀 미세 구조가 나타났다. 결론: 서로 다른 제작 방법은 코발트-크롬 합금의 물리적 성질과 파절 단면의 미세 구조에 영향을 미쳤다. 주조 방식으로 제작된 시편에서 가장 큰 표면 경도가, milling으로 제작된 시편에서 가장 큰 인장 강도를 나타냈으며, 본 연구의 모든 실험군에서 치과용 합금의 ISO 기준에 부합하는 물성을 보였다.

• Restorative Dentistry and Endodontics
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• 제18권1호
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• pp.38-53
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• 1993

The purpose of this study was to observe the resin infiltration pattern into dentin by various dentin bonding agents. Freshley extracted 36 sound human molars were used in this study. They were stored at $4^{\circ}C$ physiologic saline solution before experiment. All the teeth were cross-sectioned to expose dentin below about 3.0mm at the cusp tip and above 2.0mm at the cemento-enamel junction with Crystal Cutter (MC411 D, Maruto Co., Japan), and were made into specimens for this study (Fig. 1). The specimen experimental groups were divided into 9 groups by dentin surface treatment as following procedures: Group I: Treated with Gluma Cleanser followed by Gluma Primer and Sealer Group 2. Treated with Gluma Cleanser followed by Scotch bond 2 Adhesive Group 3: Treated with Gluma Cleanser followed by Tenure Solution A, Band Visar Seal Group 4: Treated with Scotchprep followed by Scotch bond 2 Adhesive Group 5: Treated with Scotchprep followed by Gluma Primer and Sealer Group 6: Treated with Scotch prep followed by Tenure Solution A, Band Visar Seal Group 7: Treated with Tenure Conditioner followed by Tenure Solution A, Band Visar Seal Group 8: Treated with Tenure Conditioner followed by Scotchbond 2 Adhesive Group 9: Treated with Tenure Conditioner followed by Gluma Primer and Sealer 27 specimens of 36 specimens were divided into 9 groups (Group 1-9), and were used for observation of resin tags. Remaining 9 specimens were divided into 3 groups (Group 1,4 and 7), and were used for observation of fractured dentin surfaces. Specimens to observe the resin tag were demineralized with 20% HCl for 14 hours, specimens to observe the fractured dentin surfaces were demineralized with 10% HCl for 3 minutes. All the specimens were gold-coated with Eiko ion coater (Eiko-engineering Co.), and observed under Scanning electron microscope (Hitachi S-2300) at 20 KV. The following results were obtained: 1. In group 1 treated with Gluma Cleanser, Gluma Primer, and Sealer, most resin tags were more than $100{\mu}m$. 2. In group 4 treated with Scotch prep and Scotchbond 2 Adhesive, most resin tags were about $10{\mu}m$. 3. In group 7 treated with Tenure conditioner, Tenure Solution A, B, and Visar Seal, most resin tags were about $10{\mu}m$ but occasionally resin tags were more than $100{\mu}m$. 4. In groups 2,3,5,6,8 and 9, the lengths of resin tags were inconsistent and the amount of resin tags were reduced.

• 대한치과보철학회지
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• 제41권4호
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• pp.440-450
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• 2003

Statement of problem : The joints of removable partial denture alloys have failed frequently after routine usage. Purpose : The purpose of this study was to evaluate the mechanical properties of the laser welded Co-Cr alloys. Material and method : For this study 20 Co-Cr specimens were casted and 10 of them were seperated on the middle area and laser welded with Alpha laser welding machine(Siro Lasertec, Pforzheim, Germany). Rest of them which were as cast, were used as a control group. For the section of the experimental specimens, wire cutting machine was used to make a even gap of the all specimens. Laser welding was done with manufacturer's instrunction and tested each specimen by Instron Machine. Tensile strength, 0.2% yield strength and % elongations were recorded. Fractured surfaces were investigated with SEM. Results : The results were as follows : 1. The tensile strength of the laser welded group(617.7MPa) was about 75% of the as cast group(820.4MPa). It had stastically significant differences(p<0.05). 2. The % elongation of the experimental group was 6.6 which was lower than the control group(14.3). 3. Fracture of the experimental group occured in the welded surface and showed many voids. In contrast, the fracture surface of the control group was showed rough surfaces without any voids. Conclusion : The tensile strengths of the as-cast joints were higher than those for the laser welded joints, and the % elongation of the experimental group was lower than the control group. Porosity was found in laser-welded joints.