• The Journal of Advanced Prosthodontics
• /
• v.13 no.4
• /
• pp.226-236
• /
• 2021

PURPOSE. This study aimed to evaluate the effect of incorporating zirconium oxide nanoparticles (nano-ZrO₂) in polymethylmethacrylate (PMMA) denture base resin on flexural properties at different material thicknesses. MATERIALS AND METHODS. Heat polymerized acrylic resin specimens (N = 120) were fabricated and divided into 4 groups according to denture base thickness (2.5 mm, 2.0 mm, 1.5 mm, 1.0 mm). Each group was subdivided into 3 subgroups (n = 10) according to nano-ZrO₂ concentration (0%, 2.5%, and 5%). Flexural strength and elastic modulus were evaluated using a three-point bending test. One-way ANOVA, Tukey's post hoc, and two-way ANOVA were used for data analysis (α = .05). Scanning electron microscopy (SEM) was used for fracture surface analysis and nanoparticles distributions. RESULTS. Groups with 0% nano-ZrO₂ showed no significant difference in the flexural strength as thickness decreased (P = .153). The addition of nano-zirconia significantly increased the flexural strength (P < .001). The highest value was with 5% nano-ZrO₂ and 2 mm-thickness (125.4 ± 18.3 MPa), followed by 5% nano-ZrO₂ and 1.5 mm-thickness (110.3 ± 8.5 MPa). Moreover, the effect of various concentration levels on elastic modulus was statistically significant for 2 mm thickness (P = .001), but the combined effect of thickness and concentration on elastic modulus was insignificant (P = .10). CONCLUSION. Reinforcement of denture base material with nano-ZrO₂ significantly increased flexural strength and modulus of elasticity. Reducing material thickness did not decrease flexural strength when nano-ZrO₂ was incorporated. In clinical practice, when low thickness of denture base material is indicated, PMMA/nano-ZrO₂ could be used with minimum acceptable thickness of 1.5 mm.

• Journal of the Korea Concrete Institute
• /
• v.11 no.3
• /
• pp.141-152
• /
• 1999

Precast prestressed double-tee slab may be designed by the PCI Design Handbook. It is based on the bridge construction and is required for reorganization for the use of buildings in the domestic construction environments. Much enhanced sections are developed from the reforming process on the determined design factors in the previous experimental works on double tees. Pre-determined shape, reinforcement detail, and 5000 psi concrete strength can not be expected as the best solution for the domestic construction requirements because large amount of use on that systems are anticipated. Flexural tests are performed on four full-scale 12.5m proto-type models, "least depth double tee", which are resulted from the optimization process. Domestic superimposed live load regulation, domestic material properties which is available to product, building design requirements and economy in construction are considered as the main factors to establish. the first two sections are double tee section for 1.2 ton/$\m^2$ market live load with straight and one-point depressed strands and the second two are for 0.6 ton/$\m^2$ parking live load with those strand types. All of the specimens tested fully comply with the flexural strength requirements as specified by ACI 318-95. However, the research has shown that following improved considerations are needed for better result in practice. The locations and method of connection for the lowest bottom mild bar, connection method between precast and cast-in-place concrete, and dap-end reinforcement are need to be improved.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.18 no.4 s.70
• /
• pp.417-426
• /
• 2005

Recent days composite bridge dock is gaining attraction due to many advantages such as light weight, high strength, corrosion resistance, and high durability. In this study, composite deck models of hat, box and triangular section type wore fabricated with VARTM Process. For these models, three point flexural tests wore carried out both in strong and weak axis. The experimental results were compared with each other to determine efficient section profile. It has been demonstrated that composite sandwich deck has strong potentials to be used as bridge deck in the new construction and rehabilitation works.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2004.05a
• /
• pp.347-351
• /
• 2004

[ $Si_3N_4$ ] composites have been extensively studied for engineering ceramics, because it has excellent room and high temperature strength, wear resistance properties, good resistance to oxidation, and good thermal and chemical stability. In the present work, carbon short fiber reinforced $Si_3N_4$ ceramics were fabricated by hot press method in $N_2$ atmosphere at $1800^{\circ}C$ using $Al_2O_3\;and\;Y_2O_3$ as sintering additives. Content of carbon short fiber was $0\%,\;0.1\%\;and\;0.3\%$. The composites were evaluated in terms of density, flexural strength and elastic modulus through the 3-point bending test at room temperature. Also, The wear behavior was determined by the pin on disk wear tester using silicon nitride ball. Experimental density and flexural strength decreased with increasing content of carbon fiber. But specific modulus increased with increasing content of carbon fiber. In addition, friction coefficient and specific wear loss decreased with increasing content of carbon short fiber by reason of interfacial defects between matrix and fiber.

• Journal of Technologic Dentistry
• /
• v.35 no.4
• /
• pp.271-280
• /
• 2013

Purpose: This study was to assess the effect of surface and heat treatment on the bond strength of veneering ceramics to zirconia. Methods: The specimens were divided into 7 groups according to surface treatment and heat treatment conditions prior to porcelain application. ten specimens from each group were subjected to a 3-point flexural test. In addition the influence of surface and heat treatment on surface roughness values and phase transformation of zirconia was evaluated. Statistical analysis was performed with one-way ANOVA and post hoc Tukey's test. Results: Bond strength ranged from $20.67{\pm}3.13MPa$ to $32.69{\pm}4.52$. Bond strength of surface treatment group was lower than that of control group but only $Al_2O_3$ sandblasting group was significant difference. Bond strength of heat treatment group was higher than that of surface treatment group but there was no statistical significance. Conclusion: Bond strength of veneering ceramics to zirconia was affected by surface and heat treatment.

• Steel and Composite Structures
• /
• v.34 no.3
• /
• pp.333-345
• /
• 2020

In the past, many efficient profiles have been developed for cold-formed steel (CFS) members by judicious intermediate stiffening of the cross-sections, and they have shown improved structural performance over conventional CFS sections. Most of this research work was based on numerical modelling, thus lacking any experimental evidence of the efficiency of these sections. To fulfill this requirement, experimental studies were conducted in this study, on efficient intermediately stiffened CFS sections in flexure, which will result in easy and simple fabrication. Two series of built-up sections, open sections (OS) and box sections (BS), were fabricated and tested under four-point loading with same cross-sectional area. Test strengths, modes of failure, deformed shapes, load vs. mid-span displacements and geometric imperfections were measured and reported. The design strengths were quantified using North American Standards and Indian Standards for cold-formed steel structures. This study confirmed that efficient profiling of CFS sections can improve both the strength and stiffness performance by up to 90%. Closed sections showed better strength performance whereas open sections showed better stiffness performance.

• Restorative Dentistry and Endodontics
• /
• v.46 no.3
• /
• pp.39.1-39.12
• /
• 2021

Objectives: This study analyzed the physical-chemical behavior of 2 bulk fill resin composites (BFCs; Filtek Bulk Fill [FBF], and Tetric-N-Ceram Bulk Fill [TBF]) used in 2- and 4-mm increments and compared them with a conventional resin composite (Filtek Z250). Materials and Methods: Flexural strength and elastic modulus were evaluated by using a 3-point bending test. Knoop hardness was measured at depth areas 0-1, 1-2, 2-3, and 3-4 mm. The translucency parameter was measured using an optical spectrophotometer. Real-time polymerization kinetics was analyzed using Fourier transform infrared spectroscopy. Results: Flexural strength was similar among the materials, while TBF showed lower elastic modulus (Z250: 6.6 ± 1.3, FBF: 6.4 ± 0.9, TBF: 4.3 ± 1.3). The hardness of Z250 was similar only between 0-1 mm and 1-2 mm. Both BFCs had similar hardness until 2-3 mm, and showed significant decreases at 3-4 mm (FBF: 33.45 ± 1.95 at 0-1 mm to 23.19 ± 4.32 at 3-4 mm, TBF: 23.17 ± 2.51 at 0-1 mm to 15.11 ± 1.94 at 3-4 mm). The BFCs showed higher translucency than Z250. The polymerization kinetics of all the materials were similar at 2-mm increments. At 4-mm, only TBF had a similar degree of conversion compared with 2 mm. Conclusions: The BFCs tested had similar performance compared to the conventional composite when used in up to 2-mm increments. When the increment was thicker, the BFCs were properly polymerized only up to 3 mm.

• Steel and Composite Structures
• /
• v.46 no.3
• /
• pp.353-366
• /
• 2023

This paper presents a finite-element analysis (FEA) of aluminum alloy rectangular hollow sections (RHSs) and square hollow sections (SHSs) with circular through-openings under three-point and four-point bending. First, a finite-element model (FEM) was developed and validated against the corresponding test results available in the literature. Next, using the validated FE models, a parametric study comprising 180 FE models was conducted. The cross-section width-to-thickness ratio (b/t) ranged from 2 to 5, the hole size ratio (d/h) ranged from 0.2 to 0.8 and the quantity of holes (n) ranged from 2 to 6, respectively. Third, results obtained from laboratory test and FEA were compared with current design strengths calculated in accordance with the North American Specifications (NAS), the modified direct strength method (DSM) and the modified Continuous strength method (CSM). The comparison shows that the modified CSM are conservative by 15% on average for aluminum alloy RHSs and SHSs with circular through-openings subject to bending. Finally, a new design equation is proposed based on the modified CSM after being validated with results obtained from laboratory test and FEA. The proposed design equation can provide accurate predictions of flexural capacities for aluminum alloy RHSs and SHSs with circular through-openings.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.11 no.3
• /
• pp.19-27
• /
• 1991

In this paper, fracture tests were carried out in order to investigate the fracture behavior of SFRC (Steel Fiber Reinforced Concrete) structures. Thirty six SFRC beams were used in this test. The relationships between loadings, strains, and mid-span deflections of the beams were observed under the three point loading system. From the test results, the effects of percentage of fiber by volume, the fiber aspect ratio and the initial crack depth ratio on the concrete fracture behavior were studied, and the stress intensity factors, the thoughness index, and the flexural strength of SFRC beams were calculated. According to the regression technique, some empirical formulae for predicting the flexural strength of SFRC beams were also suggested.

• Korean Journal of Materials Research
• /
• v.19 no.7
• /
• pp.391-396
• /
• 2009

2-dimensional silica-silica Continuous Fiber-reinforced Ceramic.matrix Composites (CFCCs) were fabricated by a sol-gel infilitration method that has a changing processing condition, such as the repetitions of infilitration. In order to investigate the relationship between the processing condition and the mechanical properties of composites, the mechanical properties of specimens were measured by means of a 4-point flexural strength test while the evidence of strength degradation were microstructurally characterized. There seemed to be a minimum density value that existed at which the delamination between the fabrics would not occur. In the case that the density of silica CFCCs exceeded 1.55 g/$cm^3$, the flexural strength also exceeded approximately 18 MPa at least. By applying the Minimum Solid Area (MSA) analysis of the porous structure, the correlation between the relative density and the mechanical properties of composites will be discussed.