• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.2
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• pp.383-404
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• 1997

In this study, we tried to compare the effect of glass inserts on marginal leakage of composite resin restoration by comparing with that of several filling methods. The results obtained from this experiment were as follows ; 1. The degree of microleakage measured in glass inserts group was generally lower than that of the other groups. Statistical analysis showed significant intergroup difference between glass inserts and one complete unit, pre-polymerized composite resin ball(P<.05), but no significant difference between groups of glass inserts and increments(P>.05). 2. Scanning electron microscopic observation showed relatively large gap around resin-tooth interface in specimens restored the method of using the one complete unit and pre-polymerized composite resin ball whereas a denser and tighter was observed in increments and glass inserts group. Generally the gingival margin was shown to have better bonds than the occlusal margin in specimen of all groups. 3. In the present experiment, methods using the techniques of glass inserts and increments were evaluated to be superior to those of one complete unit, pre-polymerized composite resin ball in the aspect of microleakage. However, the result of this study could not determine the superiority of the use of glass inserts over incremental method. Besides the physical properties observed in this study, the practical aspect of clinical convenience should be considered in determining the selection of material.

• Advances in materials Research
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• v.6 no.3
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• pp.245-255
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• 2017

High energy ball milling is employed to produce iron matrix- multiwall carbon nanotube (MWCNT) reinforced composite. The damage caused to MWCNT due to harsh ball milling condition and its influence on interfacial bonding is studied. Different amount of MWCNT is used to find the optimal percentage of MWCNT for avoidance of the formation of chemical reaction product at the matrix - reinforcement interface. Effect of process control agent is assessed by the use of different materials for the purpose. It is observed that ethanol as a process control agent (PCA) causes degradation of MWCNT reinforcements after milling for two hours whereas solid stearic acid used as process control agent, allows satisfactory conservation of MWCNT structure. It is further noted that at a high MWCNT content (~ 2wt.%), high energy ball milling leads to reaction of iron and carbon and forms iron carbide (cementite) at the iron-MWCNT interface. At low percentage of MWCNT, dissolution of carbon in iron takes place and the amount of reinforcement in iron matrix composite becomes negligibly small. However, under the present ball milling condition (ball to metal ratio~ 6:1 and 200 rpm vial speed) iron-1wt.% MWCNT composite of good interfacial bonding can retain the tubular structure of reinforcing MWCNT.

• Advances in nano research
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• v.7 no.6
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• pp.419-429
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• 2019

The effect of an increasing percentage of nanofiller (glass cenosphere) with Glass/Epoxy hybrid composite curved panels modeled mathematically using the multiscale concept and subsequent numerical eigenvalues of different geometrical configurations (cylindrical, spherical, elliptical, hyperboloid and flat) predicted in this research article. The numerical model of Glass/Epoxy/Cenosphere is derived using the higher-order polynomial type of kinematic theory in association with isoparametric finite element technique. The multiscale mathematical model utilized for the customized computer code for the evaluation of the frequency data. The numerical model validation and consistency verified with experimental frequency data and convergence test including the experimental elastic properties. The experimental frequencies of the multiscale nano filler-reinforced composite are recorded through the impact hammer frequency test rig including CDAQ-9178 (National Instruments) and LABVIEW virtual programming. Finally, the nano cenosphere filler percentage and different design associated geometrical parameters on the natural frequency data of hybrid composite structural configurations are illustrated through a series of numerical examples.

• Advances in materials Research
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• v.9 no.2
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• pp.133-153
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• 2020

In this paper, an improved theoretical interfacial stress and slip analysis is presented for simply supported composite steel-concrete beam bonded with an adhesive. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends, while all existing solutions neglect this effect. Remarkable effect of shear deformations of elements has been noted in the results. It is observed that large shear is concentrated and slip at the edges of the composite steel-concrete. Comparing with some experimental results from references, analytical advantage of this improvement is possible to determine the normal and shear stress to estimate exact prediction of normal and shear stress interfacial along span between concrete and steel beam. The exact prediction of these stresses will be very important to make an accurate analysis of the mode of fracture. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite steel-concrete beam. This research is helpful for the understanding on mechanical behavior of the connection and design of such structures.

• Composites Research
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• v.36 no.4
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• pp.264-269
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• 2023

Spent coffee grounds (SCG) are a ubiquitous byproduct of coffee consumption, representing a significant waste management challenge, as well as an untapped resource for economic development and sustainability. Improper disposal of SCG can result in environmental problems such as methane emissions and leachate production. This study aims to investigate the physicochemical properties of SCG and their potential as a reinforcement material in polypropylene (PP) to fabricate an eco-friendly composite via extrusion and injection molding, with SCG filler ratios ranging from 5-20%. To evaluate the effect of SCG on the morphological and mechanical properties of the bio- composite, thermogravimetric analysis, SEM, tensile, flexural, and impact tests were conducted. The results demonstrated that the addition of SCG lead to a slight increase in brittleness of the composite but did not significantly affect its mechanical properties. Impressively, the presence of a significant organic component in SCG contributed to the enhanced thermal performance of PP/SCG composites. This improvement was evident in terms of increased thermal stability, delayed onset of degradation, and higher maximum degradation temperature as compared to pure PP. These findings suggest that SCG has potential as a filler material for PP composites, with the ability to enhance the material's properties without compromising overall performance.

• Steel and Composite Structures
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• v.45 no.2
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• pp.193-204
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• 2022

The need for establishing the contribution of pultruded FRP encasements and additional FRP wraps around these encasements to the shear strength and load-deflection behavior of reinforced concrete beams is the main motivation of the present study. This paper primarily focuses on the effect of additional wrapping around the composite beam on the flexural and shear behavior of the pultruded GFRP (Glass Fiber Reinforced Polymer) beams infilled with reinforced concrete, taking into account different types of failure according to av/H ratio (arch action, shear-tension, shear-compression and pure bending). For this purpose, nine hybrid beams with variable shear span-to-depth ratio (av/H) were tested. Hybrid beams with 500 mm, 1000 mm, and 1500 mm lengths and cross-sections of 150x100 mm and 100x100 mm were tested under three-point and four-point loading. Based on the testing load-displacement relationship, ductility ratio, energy dissipation capacity of the beams were evaluated with comprehensive macro damage analysis on pultruded GFRP profile and GFRP wrapping. The GFRP wraps were established to have a major contribution to the composite beam ductility (90-125%) and strength (40-75%) in all ranges of beam behavior (shear-dominated or dominated by the coupling of shear and flexure). The composite beams with wraps were showns to reach ductilities and strength values of their counterparts with much greater beam depth.

• Steel and Composite Structures
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• v.45 no.4
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• pp.591-603
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• 2022

The flexural strengthening of reinforced concrete beams by external bonding of composite materials has proved to be an efficient and practical technique. This paper presents a study on the flexural performance of reinforced concrete continuous beams with three spans (one span and two cantilevered) strengthened by bonding carbon fiber fabric (CFRP). The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened continuous beam, i.e., the continuous concrete beam, the FRP plate and the adhesive layer. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends. Remarkable effect of shear deformations of adherends has been noted in the results. The theoretical predictions are compared with other existing solutions that shows good agreement, and It shows the effectiveness of CFRP strips in enhancing shear capacity of continuous beam. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam.

• Journal of Aerospace System Engineering
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• v.17 no.6
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• pp.82-93
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• 2023

In this paper, nonlinear transonic flutter analyses of a composite missile fin considering the effect of delamination are conducted. An effective modal analysis methodology is adopted and verified with the experimental modal test data for laminated composite plates with delamination. Extended version of the in-house computational aeroelastic analysis program with the transonic small-disturbance (TSD) code is used in order to predict the flutter dynamic pressure of the delaminated composite fin models. In the subsonic, transonic, and supersonic flow regions, nonlinear time-domain flutter analyses are performed for various delamination conditions, and aeroelastic characteristics due to the delamination phenomena are examined in detail.

• Structural Monitoring and Maintenance
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• v.10 no.3
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• pp.221-242
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• 2023

Internal and external corrosion are common in pressure pipes used in a variety of industries, often resulting in defects that compromise their integrity. This economically and industrially significant problem calls for both preventive and curative technical solutions to guarantee the reliability of these structures. With this in mind, our study focuses on the influence of composite and metallic patch repairs on the limit loads of pipes, particularly elbows, the critical component of piping systems. To this end, we used the nonlinear extended finite element method (X-FEM) to study elbows, a priori corroded on the internal surface of the extrados section, then repaired with composite and metallic patches. In addition, the effect of the geometry of composite materials and metal patches was examined, in particular the effect of their thickness and material on the increase in limit loads of repaired structures. The results obtained provide information on the effectiveness and optimization of patch repair of corroded elbows, with the aim of increasing their service life.

• Restorative Dentistry and Endodontics
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• v.34 no.1
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• pp.30-37
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• 2009

The purpose of this study was to evaluate the effect of pre-heating on some physical properties of composite resin. Eighty extracted, noncarious human molars were used in the present study. Four different temperatures of composite resin were used: $4^{\circ}C$, $17^{\circ}C$, $48^{\circ}C$, and $56^{\circ}C$. The $4^{\circ}C$ and $17^{\circ}C$ values represented the refrigerator storage temperature and room temperature respectively. For $48^{\circ}C$ and $56^{\circ}C$, composite resin was heated to the temperatures. As physical properties of composite resin, shear bond strength, microhardness, and degree of conversion were measured. The data for each group were subjected to one-way ANOVAs followed by the Tukey's HSD test at 95% confidence level. Both in enamel and dentin, among composite resin of $4^{\circ}C$, $17^{\circ}C$ $;48^{\circ}C$, and $56^{\circ}C$, the pre-heated composite resin up to $56^{\circ}C$ revealed the highest shear bond strength, and pre-heated composite resin to the higher temperature revealed higher shear bond strength. Microhardness value was also higher with composite resin of higher temperature. Degree of conversion was also higher with composite resin of the higher temperature. In this study, it seems that pre-heating composite resin up to the higher temperature may show higher shear bond strength, higher microhardness value, and higher degree of conversion. Therefore, when using composite resin in the clinic, preheating the composite resin could be recommended to have enhanced physical properties of it.