• Journal of the Korean Wood Science and Technology
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• v.44 no.4
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• pp.505-514
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• 2016

To study mechanical properties of fiberglass reinforced wood-based composite (FRWC), fiberglass with a diameter of $20{\mu}m$ was selected to prepare test specimens. Mechanical properties of fiberglass reinforced wood-based composite were determined by three-point-bending test while its microstructure was characterizes by scanning electron microscopy (SEM). The results showed that mechanical properties of fiberglass reinforced wood-based composite were superior to that of the wood fiberboard based on the contrasting mechanical curves and the analysis of fracture mechanism. It is believed that the material design with this "sandwich" structure brings a unique buffering capacity of fiberglass into play in the composites. So the specimen did not produce a sudden fracture failure at high level of applied loads because it had a bearing ability. The SEM analysis showed that the working strength of PVAc adhesive was high; under a bearing force, it could properly transfer a load. In addition, glass fiber mesh and wood fiber board combined well.

• Steel and Composite Structures
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• v.20 no.1
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• pp.43-56
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• 2016

Polyurethane foam with low density used in sandwich panels is examined in the paper. A series of experiments was carried out to identify mechanical parameters of the foam. Various experimental methods were used for determining the shear modulus, namely a four and three point bending tests (the most common in engineering practice), a double-lap shear test and a torsion test. The behavior of PU in axial compression and tension was also studied. The experiments revealed pronounced anisotropy of the PU foam. An orthotropic model is proposed. Limitations of application of isotropic model of PU in engineering practice is also discussed.

• Carbon letters
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• v.5 no.1
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• pp.18-22
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• 2004

The failure behaviours of unidirectional pultruded carbon fiber reinforced polymer (CFRP) composites were monitored by the electrical resistance measurement during tensile loading, three-point-bending, interlaminar shear loading. The tensile failure behaviour of carbon fiber tows was also investigated by the electrical resistance measurement. Infrared thermography non-destructive evaluation was performed in real time during tensile test of CFRP composites to validate the change of microdamage in the materials. Experiment results demonstrated that the CFRP composites and carbon fiber tows were damaged by different damage mechinsms during tensile loading, for the CFRP composites, mainly being in the forms of matrix damage and the debonding between matrix and fibers, while for the carbon fiber tows, mainly being in the forms of fiber fracture. The correlation between the infrared thermographs and the change in the electrical resistance could be regarded as an evidence of the damage mechanisms of the CFRP composites. During three-point-bending loading, the main damage forms were the simultaneity fracture of matrix and fibers firstly, then matrix cracking and the debonding between matrix and fiber were carried out. This results can be shown in Fig. 9(a) and (b). During interlaminar shear loading, the change in the electrical resistance was related to the damage degree of interlaminar structure. Electrical resistance measurement was more sensitive to the damage behaviour of the CFRP composites than the stress/time curve.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.8
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• pp.76-83
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• 2010

Metallic sandwich panels with pyramidal truss structures are high-stiffness and high-strength materials with low weight. In particular, bulk structures have enough space for additional multi-functionalities. In this work, in order to fabricate 3-D structures efficiently, Layered Manufacturing Method (LMM) which was composed of three steps, including crimping process, stacking process and bonding process using rapid infrared brazing, was proposed. The joining time was drastically reduced by employing infrared brazing of which heating rate and cooling rate were faster than those of conventional furnace brazing. By controlling the initial cooling rate slowly, the bonding strength was improved up to the level of strength by conventional vacuum brazing. The observation of infrared brazed specimens by optical microscope and SEM showed no defect on the joining sections. The experiments of 1-layered pyramidal structures and 2-layered pyramidal structures subject to 3-point bending were conducted to determine structural advantages of multilayered structures. From the results, the multi-layered structure has superior mechanical properties to the single-layered structure.

• Journal of Technologic Dentistry
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• v.19 no.1
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• pp.37-42
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• 1997

The interfacial bond strengh and microstructural analysis of pre-heat treated porcelain-fusedmetal(PFM) were investigated using a mechanical three-point bending tester and scanning electron microscope(SEM). Four kinds of heat treated samples were prepared as follows ; A: Heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating ${\to}1850^{\circ}F$, hold 3min under vacuum, B: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$ under vacuum conditon, C: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$, holding 3min in the air, repeat same heat treatment process under vacuum condition, D: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$, holding 1min in the air. The three-point bening test result shows that the interfacial bond strength of specimen B and C were higher than that of A and D. The SEM study indicate that Specimen C shows the highest surface density.

• The Journal of Advanced Prosthodontics
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• v.3 no.3
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• pp.136-139
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• 2011

PURPOSE. A new light curing urethane dimethacrylate and a cold curing resin with simpler and faster laboratory procedures may have even improved flexural properties. This study investigated the 3-point flexural strengths and flexural moduli of two alternate base materials. MATERIALS AND METHODS. A cold curing resin (Weropress) and a light curing urethane dimethacrylate base material (Eclipse). Along with Eclipse and Weropress, a high impact resin (Lucitone199) and three conventional base materials (QC 20, Meliodent and Paladent 20) were tested. A 3-point bending test was used to determine the flexural strengths and flexural moduli. The mean displacement, maximum load, flexural modulus and flexural strength values and standard deviations for each group were analyzed by means of one-way analysis of variance (ANOVA) (with mean difference significant at the 0.05 level). Post hoc analyses (Scheffe test) were carried out to determine the differences between the groups at a confidence level of 95%. RESULTS. Flexural strength, displacement and force maximum load values of Eclipse were significantly different from other base materials. Displacement values of QC 20 were significantly different from Lucitone 199 and Weropress. CONCLUSION. The flexural properties and simpler processing technique of Eclipse system presents an advantageous alternative to conventional base resins and Weropress offers another simple laboratory technique.

• Steel and Composite Structures
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• v.25 no.1
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• pp.35-43
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• 2017

This paper presents the findings of experimental and numerical investigations on failure analysis and structural behavior of notched steel I-beams reinforced by bonded Carbon Fiber Reinforced Polymer (CFRP) plates under static load. To find solutions for preventing or delaying the failures, understanding the CFRP failure modes is beneficial. One non-strengthened control beam and four specimens with different deficiencies (one side and two sides) on flexural flanges in both experimental test and simulation were studied. Two additional notched beams were investigated just numerically. In the experimental test, four-point bending method with static gradual loading was employed. To simulate the specimens, ABAQUS software in full three dimensional (3D) case and non-linear analysis method was applied. The results show that the CFRP failure modes in strengthening of deficient steel I-beams include end-debonding, below point load debonding, splitting and delamination. Strengthening schedule is important to the occurrences and sequences of CFRP failure modes. Additionally, application of CFRP plates in the deficiency region prevents crack propagation and brittle failure.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.3
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• pp.169-175
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• 2016

Purpose: Direct splinting material should have high flexural strength to withstand force during mastication and low modulus of elasticity to provide some movement while force applied for relief of stress. The purpose of this study was to compare flexural strength and modulus of elasticity of several resinous splinting materials. Materials and Methods: Four materials; Super-Bond C&B, G-FIX, G-aenial Universal Flo, FiltekTM Z350 XT; were used in this study. Fifteen rectangular bar specimens of each material were prepared. Three-point bending test were performed to determine physical properties. Maximum load at fracture was recorded and flexural strength and modulus of elasticity were calculated. One-way analysis of variance (ANOVA) and Scheffe's tests at a 0.05 level of significance were conducted on all test results. Results: Statistical analysis reveals that Super-Bond C&B had significant low mean value for flexible strength and the other three materials showed no significant difference. For modulus of elasticity, Super-Bond C&B exhibited statistically lower modulus of elasticity. G-FIX presented intermediate result, showing statistically higher modulus of elasticity than Super-Bond C&B but lower than G-aenial Universal Flo and FiltekTM Z350 XT. There was no significant difference on modulus of elasticity between G-aenial Universal Flo and FiltekTM Z350 XT. Conclusion: Using a G-FIX, the newly commercially available splinting material, which shows higher fracture resistance properties comparable to flowable and restorative composite resin and a relatively flexible nature might be a beneficial for stabilizing teeth mobility.

• Journal of Dental Rehabilitation and Applied Science
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• v.16 no.3
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• pp.221-227
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• 2000

Provisional fixed partial dentures(FPDs) are an important part of many prosthodontic treatment procedures. These provisional fixed prostheses must fulfill biologic, mechanical, and esthetic requirements to be considered successful. Consideration of all these factors and requirements are important because provisional resin restorations may be worn over a long period to assess the results of periodontal and endodontics therapies, and also during the restorative phase of implant reconstructive procedures. This in vitro study examined flexual strength of four resins commonly used for fixed provisional prostheses. The effects of polymerization conditions were also evaluated. The four resins tested were : Caulk Temporary bridge resin(L.D. Caulk Co. Dentsply International Millford), Jet(Lang Dental Mfg. Co. Chicago. ILL. U.S.A), Alike (Coe Laboratories. Inc. Chicago. ILL. U.S.A) and Tokuso Curefast (Coe Laboratories. Inc. Chicago. ILL. U.S.A) The test specimens were 65mm long, 14mm wide, and 3.5mm thickness. 10 specimens of four resins were cured for 15 minutes at atmospheric pressure and 10 specimens of four resins were cured at an additional pressure of approximately 20 psi. A total of 80 specimens were prepared. The flexual strength was determined by three-point bending test. Data were analysed with the Paired samples T-test and Tukey student-range test Within the limitations imposed in this study, the following conclusions can be drawn : 1. Under the condition of bench curing, Caulk Temporary bridge resin showed the highest flexual strength. In decreasing order, the flexual strength of the other materials was as follows : Jet, Tokuso Curefast, Alike, and Caulk Temporary bridge resin demonstrated significantly higher strength than other resins. 2. Under the condition of pressure curing, Jet showed the highest flexual strength. In decreasing order, the flexual strength of the other materials was as follows : Caulk Temporary bridge resin, Tokuso Curefast, and Alike. There were all statistically significant differences among four resins 3. There was a statistically significant difference between bench- and pressure-cured specimens in all four materials.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.93-98
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• 2012

In order to capture the fast crack propagation in an unmanipulated concrete fracture test, we employed mechanoluminascent(ML) material, which emits visible light when stressed, as a crack visualization tool. Three-point bending fracture test setup, a paint type ML material and a high speed camera were used to capture the images of fast moving cracks. The maximum size of coarse aggregates of concrete was used as an experimental parameter. The crack images, loading, and crack mouth opening displacement were successfully recorded as a function of time elapsed. From the test results, several interesting cracking behavior in the unmanipulated fracture test was observed in such that (1) the crack moves fast while the load is slowly decreased after the maximum loading, and (2) the crack in concrete with larger coarse aggregates moves faster than the others.