• Journal of Digital Convergence
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• v.17 no.10
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• pp.373-379
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• 2019

Polymethyl methacrylate (PMMA), a self-polymerizing resin for removable orthodontic devices, has been used as a dental orthodontic device for many years because of its advantages such as color stability, volume stability, and tissue compatibility. However, such a removable orthodontic device has a disadvantage that the longer the use in the oral cavity due to the low strength of the PMMA fracture of the orthodontic device resin in use. In this study, zinc nanoparticles (ZNP) were mixed with orthodontic PMMA to introduce strength effect. Rectangular samples ($1.4{\times}3.0{\times}19.0mm$) of orthodontic PMMA (0, 0.5, 1.0, 2.0 and 4.0%) containing ZNP were prepared. The finished specimen was tested for three-point bending strength at a speed of 1 mm / min, and the Vickers hardness was measured three times using a hardness tester. The surface roughness was measured with a surface roughness. As a result, the 3-point bending strength did not change significantly (p>0.05). Surface energy increased significantly. As a result, we successfully synthesized ZNP in this study and prepared the dispersed resin specimen for calibration. It will be possible to develop high-density dental orthodontic resins.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3396-3402
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• 2014

The importance of shape design for strength is highly regarded when applied to thin plate products in Ceramic Injection Molding (CIM), such as cases for electronic goods. This study analyzed the characteristics of the mechanical strength of CIM product by measuring the flexural strength and elastic modulus through a 3-point bending test according to the thickness of a thin plate test piece prepared by CIM. The specimen with a thickness of 0.48mm required a 82.9~94.5N fracture load, whereas a 1.0mm thick test piece required 233.6~345.8N. The increase in thickness by 0.5mm resulted in a 3-fold increase in the fracture load, whereas the elastic modulus decreased by 20%. The thicker the specimen, the lower relative density and surface hardness of the specimen. This is because the thicker the specimen, the lower the powder fraction of the ceramic mixture, and the material properties partially change after sintering.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.1
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• pp.24-31
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• 2016

Purpose: Many studies have shown that airborne-particle abrasion of fiber post can improve the bonding strength to resin cement. But, airborne-particle abrasion may influence the property of fiber post. The purpose of this study is to evaluate the influence of airborne-particle abrasion on flexural strength of fiber post. Materials and Methods: Two fiber-reinforced posts; DT Light Post Size 2 (1.8 mm diameter, Bisco Inc) and RelyX Fiber Post Size 3 (1.9 mm diameter, 3M ESPE); were used in this study. Each group was divided into 3 subgroups according to different surface treatments; without pretreatment: $50{\mu}m$ aluminum oxide (Cobra$^{(R)}$, Renfert): and $30{\mu}m$ aluminum oxide modified with silica (Rocatec Soft$^{(R)}$, 3M ESPE). After airborne-particle abrasion procedure, three-point bending test was done to determine the flexural strength and flexural modulus. The diameter of each posts was measured to an accuracy of 0.01 mm using a digital micrometer. There was no diameter change before and after airborneparticle abrasion. The mean flexural moduli and flexural strengths calculated using the appropriate equations. The results were statistically analyzed using One-way ANOVA and Scheffe's post-hoc test at 95% confidencial level. Results: There was no significant difference on flexural strength between groups. Conclusion: In the limitation of this study, flexural strength and flexural modulus of fiber post are not affected by airborne-particle abrasion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.929-933
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• 2010

Four-point bending tests were performed to investigate the interfacial adhesion of Cu-Cu bonding fabricated by thermo-compression process for three dimensional packaging. A pair of Cu-coated Si wafers was bonded under a pressure of 15 kN at $350^{\circ}C$ for 1 h, followed by post annealing at $350^{\circ}C$ for 1 h. The bonded wafers were diced into $30\;mm\;{\times}\;3\;mm$ pieces for the test. Each specimen had a $400-{\mu}m$-deep notch along the center. An optical inspection module was installed in the testing apparatus to observe crack initiation at the notch and crack propagation over the weak interface. The tests were performed under a fixed loading speed, and the corresponding load was measured. The measured interfacial adhesion energy of the Cu-to-Cu bonding was $9.75\;J/m^2$, and the delaminated interfaces were analyzed after the test. The surface analysis shows that the delamination occurred in the interface between $SiO_2$ and Ti.

• The Journal of Korean Academy of Prosthodontics
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• v.62 no.2
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• pp.95-103
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• 2024

Purpose. With the advancement of digital technology, 3D printing is being utilized in the fabrication of denture base. Nevertheless, increasing microbial adhesion to the surface of denture base has been reported as the disadvantage of 3D-printed denture base. The purpose of this study is to investigate the antifungal properties and flexural strength of 3D-printed denture base resin according to the different contents of titanium dioxide nanoparticles. Materials and methods. Titanium dioxide nanoparticles were mixed with the 3D printing resin at the ratios of 0.5, 1, 1.5, and 2 wt%. Twenty specimens per each group were printed in the form of cylindrical shape (diameter: 20 mm, height: 3 mm) to evaluate antifungal properties. Ten specimens from each group underwent polishing using autogrinder, while the remaining ten specimens did not. Candida albicans in hyphae form was inoculated onto each specimen, optical density and colony-forming unit were analyzed. The surface of the specimen was observed using scanning electron microscopy. To evaluate the flexural strength, twenty specimens per each group were 3D printed in the form of rectangular prism shape (length: 64 mm, height: 10 mm, width: 3 mm) and three-point bending tests were conducted using universal testing machine according to ISO 20795-1. Results. Colony-forming unit of C.albicans and optical density of culture medium showed no difference between non-polished groups, but decreased in the polished groups at concentration of 1, 1.5, 2 wt% titanium dioxide nanoparticles. Flexural strength increased with titanium dioxide nanoparticle at concentration of 0.5, 1, 1.5 wt%, but decreased at 2 wt% compared to 1.5 wt%. Conclusion. When 1.5 wt% of titanium dioxide nanoparticles were added to the 3D-printed denture base resin with polishing, antifungal properties were increased.

• Composites Research
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• v.13 no.3
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• pp.48-57
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• 2000

Fracture analysis of coating cracking on a substrate system described in a companion paper was applied and verified by four-point bending tests. The multiple cracking of coating was predicted using a fracture mechanics approach. The strain energy release rate (G) due to the formation of a new crack in a coating was obtained. A crack density vs. strain data of metallic and polymeric substrate was used to get the in-situ fracture toughness of coating with respect to various baking time and temperature. The $G_c$ was decreased as the baking temperature and time was increased. This paper gave insight about usefulness of four-point bending test for fracture toughness evaluation of coating and it gave a new method for in-situ coating toughness.

• Composites Research
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• v.12 no.4
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• pp.62-70
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• 1999

It was well recognized that damages associated mainly with the aging of civil infrastructrues were one of very serious problems for assurance of safety and reliability. In recent, carbon fiber sheet(CFS) has been widely used for reinforcement and rehabitation of damaged concrete beam. However, the fundamental mechanism of load transfer and its load-resistant for carbon fiber sheet reinforced concrete are not fully understood. In this study, three point bend test has been carried out to understand the damage progress and micro-failure mechanism of CFS reinforced concretes. For these purposes, four kinds of specimens are used, that is, concrete, respectively. Acoustic Emission(AE) technique was used to evaluate the characteristics of damage progress and failure mechanism of specimens. In addititon, two-dimensional AE source location was also performed to monitor crack initiation and propagation processes for four types of these specimens.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.162-172
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• 2005

The objective of this research works is to investigate into characteristics of bending stiffness and failure for the ISB ultra-lightweight panel with internally structured material. The expanded metal with a crimped pyramid shape and woven metal are employed as an internally structured material. Through three-points bending test, the force-displacement curve and failure shape are obtained to examine the deformation pattern, characteristic data, such as maximum load, displacement at maximum load, etc, and failure pattern of the ISB panel. In addition, the influence of design parameters fur ISB panel on the specific stiffness, the specific stiffness per unit width, failure mode and failure map has been found. Finally, it has been shown that ISB containing expand metal with the crimped pyramidal shape is prefer to that containing woven metal from the view point of optimal design for ISB panel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.963-970
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• 2015

Laminate structures are used in the automobile, aerospace, and display industries. The advantages of fiber metal laminates are well known. Fiber metal laminates are useful for reducing the weight and improving impact resistance . However, currently, the mechanical properties of fiber metal laminates are not derived. In this paper, we use thickness as a factor for comparing the properties of laminates of various thickness combinations. The properties fiber metal laminates are analyzed using design of experiments. In addition, the finite element method is used to analyze elastic and plastic strains of fiber metal laminates and aluminum plates. The final goal of this paper is to find a suitable finite element model of fiber metal laminates under bending.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.49-56
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• 1999

Welding is a reliable process and is mainly adopted for fabricating heavy structures. Recently, transverse cracks in the weld metal is serious problem, and they affect cost, efficiency, safety and joint reliability for various welded structures. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained are as follows; 1) The content of diffusible hydrogen in the commercial flux cored are welding wire was remarkable change by manufacturer. 2) The diffusible hydrogen content was thd main factor for weld metal transverse cracks. 3) Weld metal was immune to transverse cracking under the condition of low diffusible hydrogen content of high restraint condition. 4) The factors for weld metal transverse crack would be the content of diffusible hydrogen and restraint of weld joint.