• Journal of Dental Rehabilitation and Applied Science
• /
• v.36 no.1
• /
• pp.41-47
• /
• 2020

Purpose: The purpose of this study was to evaluate the flexural strength and reliability of highly translucent colored zirconia for all ceramic restoration. Materials and Methods: Bar-shaped specimens (25 × 4 × 2.5 mm) were prepared from highly translucent monolithic zirconia. Three experimental groups were set up according to color (shade A0, A1, and A3). For each group, 20 specimens were prepared. Flexural strength was determined using a 3-point flexural test and results were analyzed with one-way ANOVA test. Weibull statistical analysis provided 2 parameter estimates: Weibull modulus and characteristic strength. X-ray diffraction (XRD) analysis was performed. Results: There was statistically significant difference between uncolored (Shade A0) and colored (shade A1 and A3) (P < 0.05), but there was no difference between colored groups (P > 0.05). The uncolored group had higher reliability compared with colored study groups. On x-ray diffraction analysis of each group, typical peaks of tetragonal phase appeared in all groups. Conclusion: Within the limitations of this in vitro study, coloring highly translucent zirconia had significant effect on flexural strength and reliability. Therefore, clinicians should be careful when using highly translucent colored zirconia to prevent breakage of veneering ceramic and enhance aesthetics.

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

• Composites Research
• /
• v.26 no.5
• /
• pp.295-302
• /
• 2013

In this study, Al5052/CFRP composites were fabricated for an automobile component by compression molding process inside a U-channel mold. Al5052 sheet were treated by sand blasting with two different particle sizes. Accordingly, surface roughness (Ra) values of $4.25{\mu}m$ and $1.85{\mu}m$ were obtained for the treated Al5052 sheets. The effect of surface roughness of Al5052 sheets on the adhesion and mechanical properties of Al5052/CFRP composites have been evaluated. Shear lap test and 3-point bending test were conducted. Results showed that the shear load for the composite fabricated by using the treated Al5052 sheets with Ra value of $1.85{\mu}m$ and $4.25{\mu}m$ were 3 and 5 times higher than Ra value of $0.73{\mu}m$ of the composite fabricated by using the untreated sheet. The bending stress of 200MPa was obtained for the composite fabricated with untreated Al5052 sheets. The bending stress increased to 400MPa when the composite fabricated from treated sheets. However, the bending stress was not influenced by treating condition through sand blasting.

• Composites Research
• /
• v.18 no.1
• /
• pp.30-37
• /
• 2005

The bending strength characteristics and local deformation behaviors of honeycomb sandwich composites were investigated using three-point bending experiment and finite element simulation with a real model of honeycomb core. Two kinds of cell sizes of honeycomb core, two kinds of skin layer thicknesses, perfect bonding specimen as well as initial delamination specimen were used for analysis of stress and deformation behaviors of honeycomb sandwich beams. Various failure modes such as skin layer yielding, interfacial delamination, core shear deformation and local buckling were considered. Its simulation results were very comparable to the experimental ones. Consequently, cell size of honeycomb core and skin layer thickness had dominant effects on the bending strength and deformation behaviors of honeycomb sandwich composites. Specimens of large core cell size and thin skin layer showed that bending strength decreased by $30\~68\%$.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.29 no.4
• /
• pp.327-336
• /
• 2013

This study aimed to investigate the reinforcing effect of two kinds of glass fiber, Quarts Splint$^{TM}$ Mesh and SES MESH$^{(R)}$ and to evaluate the effect of the thermocycling on the transverse strength of the denture base and on the reinforcing effect of the reinforcements. 20 specimens of the size of $2.5{\times}10.0{\times}65.0mm$ were fabricated for each group; control group, metal mesh reinforcement group, Quarts Splint$^{TM}$ Mesh reinforcement group and SES MESH$^{(R)}$ reinforcement group. To find the difference made by the thermocycling, 10 specimens of each reinforcement group were treated by thermocycling. 3-point bending test was performed to measure the transverse strength of the denture base resin. The specimens reinforced with SES MESH$^{(R)}$ and Quarts Splint$^{TM}$ Mesh showed significantly higher transverse strength than the control group (P<.05), and significantly lower transverse strength than the specimens reinforced with the metal mesh (P<.05). Thermocycled specimens were lower in transverse strength than non-thermocycled specimens in the control group, metal mesh group, Quarts Splint$^{TM}$ Mesh group and SES MESH$^{(R)}$ group, however significant difference (P<.05) was found only in the control group.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.10
• /
• pp.688-695
• /
• 2017

Compared to metal, CFRP has excellent mechanical characteristics in terms of intensity, hardness, and heat resistance as well as its light weight that it is used widely in various fields. Therefore, this material has been used recently in the aerospace field. On the other hand, the material has shortcomings in terms of its extreme vulnerability to damage occurring internally from an external impact. This study examined the intensity up to its destruction from repeated use with the internal impact of a CFRP laminated plate that had also been exposed to external impact obtain design data for the external plate of aircraft used in the aerospace field. For the experimental method, regarding the quasi-isotopic type CFRP specimen and orthotropic CFRP specimen that are produced with a different layer structure, steel spheres with a diameter of 5 mm were collided to observe the resulting impact damage. Through a 3-point flexural fatigue experiment, the progress of internal layer separation and impact damage was observed. Measurements of the flexural fatigue strength after the flexural fatigue experiment until internal damage occurs and the surface impacted by the steel spheres revealed the quasi-isotopic layer structure to have a higher intensity for both cases.

• Journal of Digital Convergence
• /
• v.18 no.4
• /
• pp.341-346
• /
• 2020

Polymethyl methacrylate (PMMA), a self-curing resin mainly used in removable orthodontic appliances, is an acrylic resin mainly used in the field of modern dentistry. As an advantage, it has been used for a long time as a material for orthodontic devices in dentistry due to its color and volume, tissue affinity, and stability. The production of PMMA can be divided into self-polymerization method and thermal polymerization method according to activation method. Self-curing resins have long been used as orthodontic devices. The resin injection method is largely divided into a sprinkle-on method and a mixing method. In this study, we intend to test the mechanical properties according to the resin injection method of the orthodontic device, such as strength, modulus of elasticity, and surface roughness. There was no significant difference in strength as a result of three-point bending strength test on rectangular specimens (1.4 × 3.0 × 19.0 mm) of orthodontic PMMA. There was also no significant difference in hardness. There was no significant difference in surface roughness. It was confirmed that the orthodontic PMMA had no significant difference in mechanical properties according to the resin injection method of the orthodontic device.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.9 no.3
• /
• pp.45-54
• /
• 2009

This study was developed the metallic plate for bone fixation in the neurosurgery and general surgery and plates has a finn place in bone operating and treatment. The plates can be realized to bending strength and stiffness for strength estimation. Maximum point of bending curves has a bending point(P) with maximum load which to applied nearly 0.2% offset displacement. The device's sizing has a ${\Phi}13$ and ${\Phi}18$, and algorithm of strength estimation compared a plate(${\Phi}13$, ${\Phi}18$, ${\Phi}13-{\Phi}18$). The bending strength of the curved metallic plate has to evaluate maximum of a 311N, 387N, 410N, 474N. When a displacement preserve with a load, tensile stress through to press a plate is 274N, 324N, 382N, 394N. The algorithm of strength estimation can be used to support estimation of bending strength and stiffness. Their tool bring to settlement in the new basic algorithm for evidence with varied adjustment.

• Composites Research
• /
• v.19 no.6
• /
• pp.23-31
• /
• 2006

We measured mechanical properties, including Young's modulus, effective bending modulus and nominal fracture strength of nanohoneycomb structures using an Atomic Force Microscope(AFM) and a Nano-Universal Testing Machine(UTM). Anodic aluminum oxide(AAO) films are well suited as nanohoneycomb structures because of the simple fabrication process, high aspect ratio, self-ordered hexagonal pore structure, and simple control of pore dimensions. Bending tests were carried out for cantilever structures by pressing AFM tips, and the results were compared with three-point bending tests and tensile tests using a Nano-UTM. One side of the AAO films is clogged by harrier layers, and looks like a face material of conventional sandwich structures. Analysis of this layer showed that it did not influence the bending rigidity, and was just a crack tip. The present results can act as a design guideline in applications of nanohoneycomb structures.

• Korean Journal of Dental Materials
• /
• v.44 no.3
• /
• pp.273-280
• /
• 2017

The aim of the present study was to investigate the effects of specimen dimension on the flexural properties and testing reliability of dental composite resin. The composite resin was prepared experimentally by mixing a resin matrix with silanated micrometer glass filler at 50 vol%. Flexural specimens with various dimension in specimen's width were fabricated by light curing using a split metal mold; $25{\times}2{\times}2mm$, $25{\times}2{\times}4mm$, $25{\times}2{\times}6mm$ in length ${\times}$ height ${\times}$ width. The flexural strength and modulus were determined according to ISO 4049 test protocol at a span length of 20 mm (normal-flexural strength; NFS). Another flexural test was conducted using mini-sized specimens ($12{\times}2{\times}2mm$, $12{\times}2{\times}4mm$, $12{\times}2{\times}6mm$) from the broken specimens at a span length of 10 mm (mini-flexural strength; MFS). Data were analyzed with ANOVA and Duncan's post-hoc test and the test reliability was evaluated by Weibull analysis. Results showed that there are generally no significant difference in flexural strength with the increase in the specimen width in NFS and MFS tests. However, the test reliability of flexural strength based on Weibull analysis was largely changed with the variables in the dimension of width and span length. The flexural modulus of NFS was increased as the dimension of specimens width increased while there was no trend in flexural modulus of MFS test. Overall results recommend that the evaluation of flexural properties and the reliability of dental composite resins should be performed with more than one test method.