• The Journal of Korean Academy of Prosthodontics
• /
• v.33 no.1
• /
• pp.1-12
• /
• 1995

For the purpose of this study, the silicoating on Ni-Cr-Be alloy surface was carried out by using the Silicoater MD. The effect of time delay after silicoating on the bond strength between the metal and resin cement was examined. The groups were divided into 4 : group 1 : Sandblasted with $250{\mu}m$ aluminium oxide, immediatly cemented group 2 : Sandblasted with $250{\mu}m$ aluminium oxide, silicoated and immediatly cemented group 3 : Sandblasted with $250{\mu}m$ aluminium oxide, silicoated and cemented after 7 days group 4 : Sandblasted with $250{\mu}m$ aluminium oxide, silicoated and coated with unfilled resin and cemented after 7 days Specimens were luted with Comspan, Superbond C&B or Panavia EX. The tensile bond strength between the metal and resin cement was measured by using the universal testing machine. The results were as follows : 1. The bond strength in groups 2, 3 and 4 was higher than that of group 1 (p<0.05). There was no statistically significant difference among the bond strength in groups 2, 3 and 4 (p>0.05). 2. In Comspan-cemented groups, there was no significant difference among the bond strength in groups 2, 3 and 4 (p<0.05). 3. In Panavia EX-cemented groups, the bond strength of group 3 was higher than that of group 2 (p<0.05) and there was no significant difference between groups 3 and 4. 4. In Superbond C&B-cemented groups, there was significant difference between groups 2 and 3 (p<0.05) and the bond strength of group 4 was higher than that of group 3 (p<0.05). 5. The highest tensile bond strength was obtained by using the Superbond C&B and no difference in the Panavia EX and Comspan. 6. The modes of bond failure were mainly cohesive failure. The method of storage and transport indicated in this study seems recommendable for laboratory and clinical use at least up to 7 days.

• International Journal of Concrete Structures and Materials
• /
• v.11 no.2
• /
• pp.343-363
• /
• 2017

The objective of this work was finding out the most advisable testing conditions for an effective and robust characterization of the tensile strength (TS) of concrete disks. The independent variables were the loading geometry, the angle subtended by the contact area, disk diameter and thickness, maximum aggregate size, and the sample compression strength (CS). The effect of the independent variables was studied in a three groups of experiments using a factorial design with two levels and four factors. The likeliest location where failure beginning was calculated using the equations that account for the stress-strain field developed within the disk. The theoretical outcome shows that for failure beginning at the geometric center of the sample, it is necessary for the contact angle in the loading setup to be larger than or equal to a threshold value. Nevertheless, the measured indirect tensile strength must be adjusted to get a close estimate of the uniaxial TS of the material. The correction depends on the loading geometry, and we got their mathematical expression and cross-validated them with the reported in the literature. The experimental results show that a loading geometry with a curved contact area, uniform load distribution over the contact area, loads projected parallel to one another within the disk, and a contact angle bigger of $12^{\circ}$ is the most advisable and robust setup for implementation of BT on concrete disks. This work provides a description of the BT carries on concrete disks and put forward a characterization technique to study costly samples of cement based material that have been enabled to display new and improved properties with nanomaterials.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.5
• /
• pp.103-110
• /
• 2005

In this paper, the characteristics of excessive horizontal stress components in Korea were studied using more than five hundred measured data set of in-situ hydraulic fracturing test. Based on the in-situ testing data, the magnitude and orientation of the horizontal stress component and variation of stress ratio (K) with depth were investigated. And also horizontal stress magnitude versus depth relationships and distribution limits of stress ratio components were suggested. For the depth less than 310 m in the entire territory, the stress ratio has a tendency to diminish and stabilize with depth, but fur some areas, it was revealed that the excessive horizontal stress fields with stress ratio close to 3.0 below 200 m in depth have formed. The results from the investigation of excessive horizontal stress regions showed that there existed several regions where the localized excessive horizontal stress was big enough to potentially induce brittle failure around the openings at less than 300 m in depth.

• Journal of Digital Convergence
• /
• v.12 no.3
• /
• pp.219-226
• /
• 2014

In this study, reliability software cost model considering shape parameter based on life distribution from the process of software product testing was studied. The shape parameter using the Erlang and Log-logistic model that is widely used in the field of reliability problems presented. The software failure model was used finite failure non-homogeneous Poisson process model, the parameters estimation using maximum likelihood estimation was conducted. In comparison result of software cost model based on the Erlang distribution and the log-logistic distribution software cost model, because Erlang model is to predict the optimal release time can be software, but the log-logistic model to predict to optimal release time can not be, Erlang distribution than the log-logistic distribution appears to be effective. In this research, software developers to identify software development cost some extent be able to help is considered.

• Structural Engineering and Mechanics
• /
• v.44 no.6
• /
• pp.775-799
• /
• 2012

This work approaches the structural performance of masonry arches that have a small ratio between number of vossoirs and span length. The aim of this research is to compare and validate three different methods of analysis (funicular limit analysis F.L.A., kinematic limit analysis K.L.A. and plane stress Finite Element Analysis F.E.A.) with an experimental campaign. 18 failure tests with arches of different shapes and boundary conditions have been performed. The basic failure mechanism was the formation of enough hinges in the geometry. Nevertheless, in few cases, sliding between vossoirs also played a relevant influence. Moreover, few arches didn't reach the collapse. The FLA and KLA didn't find a solution close to the experimental values for some of the tests. The low number of vossoirs and joints become a drawback for an agreement between kinematic mechanism, equilibrium of forces and geometry constraints. FLA finds a lower bound whereas KLA finds an upper bound of the ultimate load of the arch. FEA is the most reliable and robust method and it can reproduce most of the mechanism and ultimate loads. However, special care is required in the definition of boundary conditions for FEA analysis. Scientific justification of the more suitability of numerical methods in front of classic methods at calculating arches with a few vossoirs is the main original contribution of the paper.

• Journal of the Korea Society of Computer and Information
• /
• v.15 no.5
• /
• pp.125-132
• /
• 2010

Decision problem called an optimal release policies, after testing a software system in development phase and transfer it to the user, is studied. The applied model of release time exploited infinite non-homogeneous Poisson process. This infinite non-homogeneous Poisson process is a model which reflects the possibility of introducing new faults when correcting or modifying the software. The failure life-cycle distribution used exponential and non-exponential family which has various intensity. Thus, software release policies which minimize a total average software cost of development and maintenance under the constraint of satisfying a software reliability requirement becomes an optimal release policies. In a numerical example, after trend test applied and estimated the parameters using maximum likelihood estimation of inter-failure time data, estimated software optimal release time.

• Journal of Digital Convergence
• /
• v.11 no.9
• /
• pp.159-166
• /
• 2013

In this paper, make a study decision problem called an optimal release policies after testing a software system in development phase and transfer it to the user. When correcting or modifying the software, finite failure non-homogeneous Poisson process model, presented and propose release policies of the life distribution, half-logistic property model which used to an area of reliability because of various shape and scale parameter. In this paper, discuss optimal software release policies which minimize a total average software cost of development and maintenance under the constraint of satisfying a software reliability requirement. In a numerical example, the parameters estimation using maximum likelihood estimation of failure time data, make out estimating software optimal release time. Software release time is used as prior information, potential security damages should be reduced.

• The Journal of Advanced Prosthodontics
• /
• v.7 no.6
• /
• pp.454-459
• /
• 2015

PURPOSE. To determine whether the fracture strengths and failure types differed between metal and zirconia frameworks veneered with pressable or layering ceramics. MATERIALS AND METHODS. A phantom molar tooth was prepared and duplicated in 40 cobalt-chromium abutments. Twenty metal (IPS d.SIGN 15, Ivoclar, Vivadent, Schaan, Liechtenstein) and 20 zirconia (IPS e.max ZirCAD, Ivoclar) frameworks were fabricated on the abutments. Each framework group was randomly divided into 2 subgroups according to the veneering material: pressable and layering ceramics (n=10). Forty molar crowns were fabricated, cemented onto the corresponding abutments and then thermocycled ($5-55^{\circ}C$, 10,000 cycles). A load was applied in a universal testing machine until a fracture occurred on the crowns. In addition, failure types were examined using a stereomicroscope. Fracture load data were analyzed using one-way ANOVA and Tukey HSD post-hoc tests at a significance level of 0.05. RESULTS. The highest strength value was seen in metal-pressable (MP) group, whereas zirconia-pressable (ZP) group exhibited the lowest one. Moreover, group MP showed significantly higher fracture loads than group ZP (P=.015) and zirconia-layering (ZL) (P=.038) group. No significant difference in fracture strength was detected between groups MP and ML, and groups ZP and ZL (P>.05). Predominant fracture types were cohesive for metal groups and adhesive for zirconia groups. CONCLUSION. Fracture strength of a restoration with a metal or a zirconia framework was independent of the veneering techniques. However, the pressing technique over metal frameworks resisted significantly higher fracture loads than zirconia frameworks.

• Restorative Dentistry and Endodontics
• /
• v.23 no.1
• /
• pp.487-501
• /
• 1998

In the case of CAD/CAM ceramic inlay restorations, if isthmus width is widened too much, it may cause fracture of remaining tooth structure or loss of bonding at the luting interface because of excessive displacement of buccal or lingual cusps under occlusal loads. So to clarify the criterior of widening isthmus width, this study was designed to test the tensile bond strength and bond failure mode between dentin and ceramic cemented with luting composite resin cements. Cylindrical ceramic blocks(Vita Cerec Mark II, d=4mm) were bonded to buccal dentin of 40 freshly extracted third molars with 4 luting composite resin cements(group1 : Scotchbond Resin Cement/Scotchbond Multi-Purpose, group2 : Duolink Resin Cement/ All-Bond 2, group3: Bistite Resin Cement/Ceramics Primer, and group4:Superbond C&B). Tensile bond test was done under universal testing machine using bonding and measuring alignment blocks(${\phi}ilo$ & Urn, 1992). After immersion of fractured samples into 1 % methylene blue for 24 hours, failure mode was analysed under stereomicroscope and SEM. Results: The tensile bond strength of goup 1, 2 & 4 was $13.97{\pm}2.90$ MPa, $16.49{\pm}3.90$ MPa and $16.l7{\pm}4.32$ MPa, respectively. There was no statistical differences(p>0.05). But, group 3 showed significantly lower bond stregnth($5.98{\pm}1.l7$ MPa, p<0.05). In almost all samples, adhesive fractures between dentin and resin cements were observed. But, in group 1, 2 & 4, as bond strength increased, cohesive fracture within resin cement was observed simultaneously. And, in group 3, as bond strength decreased, cohesive fracture between hybrid layer and composite resin cement was also observed. Cohesive fracture within dentin and porcelain adhesive fracture were not observed. In conclusion, although adhesive cements were used in CAD/CAM -fabricated ceramic inlay restorations, the conservative priciples of cavity preparation must be obligated.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.8 no.1
• /
• pp.211-220
• /
• 2004

This paper presents the evaluation of pullout strengths of expansion anchors and wedge anchors that can cause a failure of the concrete on the basis of the design for anchorage. Tests are conducted for heavy-duty anchors and wedge anchors domestically manufactured and to be installed in plain concrete member. The mainly testing parameters reflected the effects of edge distance. Design of post-installed steel anchors is presented by the Concrete Capacity Design(CCD) in European Organization for Technical Approval. This approach is compared to the well-known provisions, ACI 349-90 specification. The use of both methods to predict the concrete failure load of expansion anchor in uncracked concrete under monotonic loading for important applications is compared. In this study, the concrete tension capacity of fastenings with Heavy-duty Anchors and Wedge Anchors in plain concrete predicted by ACI 349-90 and the Concrete Capacity Design method has been compared with the results of tests.