• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.88-93
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• 2002

The objective of this study is to obtain fundamental understandings involving the manufacturing process of nano-composite via resin transfer molding and explore the role of nano sized $Fe_2O_3$ particles in the epoxy/$Fe_2O_3$ nano-composites. To achieve this goal, following investigations have been conducted: Define the optimum dispersion technique of nano-particles, identify the effect of the nano-particles to the resin viscosity, characterize the key mechanical properties versus particle loading amounts, and explore the usefulness and quality improvement in nano-composites. These efforts will be useful for designers to quantify application payoffs and define a technology development roadmap for manufacturing nano-composites, and will help an engineering design and manufacturing nano-composites more efficiently by providing the design methodology.

• Journal of the Korean Wood Science and Technology
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• v.18 no.4
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• pp.86-101
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• 1990

The primary objective of this research was to investigate the strength properties of Comply, a composite panel. fabricated with particle board as core material and veneer or plywood as face and back. 20types of comply composites were manufactured according to the four specific gravity levels(0.5, 0.6, 0.7 or 0.8) of particleboard core and three veneer or two plywood thicknesses for face and back. They were tested and compared with matching particleboard (control) on moisture content. specific gravity, bending properties(MOE, MOR SPL). nail resistance and internal bond strength. The obtained results were summarized as follows: The increasing effect of modulus of elasticity was shown by the increase of face and back veneer or plywood thickness. The modulus of rupture and stress at proportional limit of the comply composites bonded with 3mm thick veneers or 3mm thick plywood face and back were higher than 2mm thick veneer or 2mm thick plywood as face and back. Both of modulus of rupture and stress at proportional limit on bending of Comply were higher than those of control board. Also the modulus of elasticity of Comply showed much higher than that of control board. The nail resistance of Comply, composed of plywood as face and back was higher than that of veneer. The nail resistance of control board was higher than that of Comply at Sp.Gr 0.7 and 0.8 core boards. Internal bond of Comply, composed of 1mm and 2mm thick veneer as face and back was higher than that of 3mm thick veneer. The increasing effect of modulus of elasticity was shown by the increase of shelling ratio in Comply composed of veneer and plywood as face and back. The modulus of rupture was increased by the increment of shellmg ratio in Compiy, composed of plywood as face and back. The modulus of elasticity and modulus of. rupture of comply were higher than those of particleboard(control) in effect of shelling ratio. Therefore it was concluded that the mechanical property values of Comply were clearly greater than those of particleboard(control).

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.118-128
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• 1999

There are many ultrasonic measurement methods that are used in nondestructive testing applications. Some typical applications include material property determination, microstructural characterization. and flaw detection. Ultrasonic parameters such as velocity and attenuation are most commonly required in these applications. The accuracy and repeatability of testing results are dependent on both the hardware used to generate and receive the ultrasonic waves and on the analysis software for calculating these parameters. In this study, five analysis algorithms were implemented on a computer for measuring wave speed in a pulse echo. immersion testing configuration. In velocity measurements comparisons were made between the overlap. cross-correlation. Fourier transform. Hilbert transform, wavelet transform algorithms. Velocity measurement was applied to an isotropic steel sample using the five analysis algorithms. Frequency-dependent phase/group velocity and attenuation were also measured using the Fourier transform and wavelet transform algorithms on a composite laminate containing voids.

• Geomechanics and Engineering
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• v.28 no.6
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• pp.599-611
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• 2022

Tendon reinforced cemented soil is applied extensively in foundation stabilisation and improvement, especially in areas with soft clay. To solve the deterioration problem led by steel corrosion, the glass fiber-reinforced polymer (GFRP) tendon is introduced to substitute the traditional steel tendon. The interface bond strength between the cemented soil matrix and GFRP tendon demonstrates the outstanding mechanical property of this composite. However, the lack of research between the influence factors and bond strength hinders the application. To evaluate these factors, back propagation neural network (BPNN) is applied to predict the relationship between them and bond strength. Since adjusting BPNN parameters is time-consuming and laborious, the particle swarm optimisation (PSO) algorithm is proposed. This study evaluated the influence of water content, cement content, curing time, and slip distance on the bond performance of GFRP tendon-reinforced cemented soils (GTRCS). The results showed that the ultimate and residual bond strengths were both in positive proportion to cement content and negative to water content. The sample cured for 28 days with 30% water content and 50% cement content had the largest ultimate strength (3879.40 kPa). The PSO-BPNN model was tuned with 3 neurons in the input layer, 10 in the hidden layer, and 1 in the output layer. It showed outstanding performance on a large database comprising 405 testing results. Its higher correlation coefficient (0.908) and lower root-mean-square error (239.11 kPa) were obtained compared to multiple linear regression (MLR) and logistic regression (LR). In addition, a sensitivity analysis was applied to acquire the ranking of the input variables. The results illustrated that the cement content performed the strongest influence on bond strength, followed by the water content and slip displacement.

• Composites Research
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• v.37 no.2
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• pp.132-138
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• 2024

In this study, a molecular dynamics simulation study was performed to investigate the size-dependent electroelastic properties of single-walled boron nitride nanotubes(BNNT). To describe the elasticity and polarization of BNNT under mechanical loading, the Tersoff potential model and rigid ion approximation were adopted. For the prediction of piezoelectric constants and Young's modulus of BNNTs, piezoelectric constitutive equations based on the Maxwell's equation were used to calculate the strain-electric displacement and strain-stress relationships. It was found that the piezoelectric constants of BNNTs gradually decreases as the radius of the tubes increases showing a nonnegligible size effect. On the other hand, the elastic constants of the BNNTs showed opposites trends according to the equivalent geometrical assumption of the tubular structures. To establish the structure-property relationships, localized configurational change of the primarily bonded B-N bonded topology was investigated in detail to elucidate the BNNT curvature dependent elasticity.

• Elastomers and Composites
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• v.59 no.2
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• pp.51-63
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• 2024

Polypropylene (PP) is a commodity plastic that is widely used owing to its cost-effectiveness, lightweight nature, easy processability, and outstanding chemical and thermomechanical characteristics. However, the imperative to address energy and environmental crises has spurred global initiatives toward a circular economy, necessitating sustainable alternatives to traditional fossil-fuel-derived plastics. In this study, we conducted a series of comparative investigations of bio-based polypropylene (bio-PP) blends with current PP of the same and different grades. An extrusion-based processing methodology was employed for the bio-PP composites. Talc was used as an active filler for the preparation of the composites. A comparative analysis with the current petroleum-based PP indicated that the thermal properties and tensile characteristics of the bio-PP blends and composites remained largely unaltered, signifying the feasibility of bio-PP as a potential substitute for the current PP. To achieve a higher Young's modulus, elongation at break (EAB), and melt flow index (MFI), we prepared different composites of PP of different grades and bio-PP with varying talc contents. Interestingly, at higher biomass contents, the composites exhibited higher MFI and EAB values with comparable Young's moduli. Notably, the impact strengths of the composites with various biomass and talc contents remained unaltered. In-depth investigations through surface analysis confirmed the uniform dispersion of talc within the composite matrix. Furthermore, the moldability of the bio-PP composites was substantiated by comprehensive rheological property assessments encompassing shear rate and shear viscosity. Thus, from these outcomes, the fabricated bio-PP-based composites could be an alternative to petroleum-based PP composites for sustainable automobile applications.

• Journal of the Korea Institute of Building Construction
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• v.14 no.4
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• pp.308-313
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• 2014

Recently, for longevity of resident building, the main trend is that the change of the inside space organization of resident building from wall construction to rhamen construction, which resulted in increase in use of lightweight composite panel. Thus, in this study, authors analyzed the engineering property of oxide of magnesium depending on the magnesium chloride addition ratio. The results of this research is expected to contribute on providing a fundamental material for the surface materials of lightweight composite panel. As the result of the experiment, as fluidity increased, air content decreased and initial set and final set as the magnesium chloride addition ratio increase. In the aspect of flexural strength and compressive strength, the test specimen showed the highest strength at 40% of the magnesium chloride addition ratio. At 20% of the magnesium chloride addition ratio, the test specimen showed the lowest water absorption rate. As the magnesium chloride addition ratio increases, the expansibility tends to increase as well in the aspect of shrinkage strain. After observing microstructure, we can see hydration products in the form of needle. It appeared high flexural strength because the hydration products have mineral fibrous tissue shape, which also contribute to the cause of the expansibility.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.4
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• pp.329-340
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• 2006

Statement of problem: Damping of the peak force transmitted to implants has been reported by in vitro studies using impact forces on resin-veneered superstructures. Theoretical assumptions suggest that use of acrylic resin for the occlusal surfaces of a prosthesis would protect the connection between implant and bone. Therefore, the relationship between prosthesis materials and the force transmitted through the implant system also needs to be investigated under conditions that resemble the intraoral mechanical environment. Purpose: The purpose of this study was to analyze the fracture strength and modes of temporary prosthesis when a flange or occlusally extended structure were connected on the top of the abutment. Material and method: Modified abutments of winged and bulk design were made by casting the desired wax pattern which is made on the UCLA type plastic cylinder. Temporary crowns were made using templates on the modified abutments, and its fracture toughness and strain were compared to the traditional temporary prosthesis. To evaluate the effect of aging, 5.000 times of thermocycling were performed, and their result was compared to the 24hours specimen result. Results: The following conclusions were drawn from this study: 1. In the fracture toughness test, temporary crown's fracture line located next to the screw hole while modified designs with metal support showed fracture line on the metal and its propagation along the metal-resin interface. 2. Wing and bulk structure didn't show significant difference in the fracture toughness (p>0.05), but wing structure showed stress concentration on the screw hole area compared to bulk structure which showed even stress distribution. 3. In the fracture toughness test after thermocycling, wing and bulk structure showed increased or similar results in metal supported area while off-metal area and temporary crown showed decreased results. 4. In the strain measurement after thermocycling, its value increased in the temporary and bulk structure. However, wing structure showed decreased value in the loading point while increased value in the screw hole area. Conclusion: Wing type design showed compatible result to the bulk type that its application with composite resin prosthesis to the implant dentistry is considered promising.

• Applied Microscopy
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• v.40 no.3
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• pp.155-162
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• 2010

Bone is a hierarchically structured composite material which has been well studied by the materials engineering community because of its unique structure and mechanical properties. Bone is a laminated organic-inorganic composite composed of primarily hydroxyapatite, collagen and water. The main mineral that gives bone's hardness is calcium phosphate, which is also known as hydroxyapatite. Light microscopy (LM) and transmission electron microscopy (TEM) were used to study the structure of femurs from chicken and rabbit. The elemental analysis was used to search variation in the distribution of calcium, potassium and oxygen in the femur. Current investigation focused on two structural scales: micro scale (arrangement of compact bone) and nano scale (collagen fibril and apatite crystals). At micro scale, distinct difference was found in microstructures of chicken femur and rabbit femur. At nano scale, we analyzed the shape and size of apatite crystals and the arrangement of collagen fibril. Consequently, femurs of chicken and rabbit had very similar chemical property and structures at nano scale despite of their different species.

• Korean Journal of Materials Research
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• v.18 no.6
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• pp.339-346
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• 2008

Single-crystal $ZnIn_2S_4$ layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at $450^{\circ}C$ with a hot wall epitaxy (HWE) system by evaporating a $ZnIn_2S_4$ source at $610^{\circ}C$. The crystalline structures of the single-crystal thin films were investigated via the photoluminescence (PL) and Double-crystal X-ray rocking curve (DCRC). The temperature dependence of the energy band gap of the $ZnIn_2S_4$ obtained from the absorption spectra was well described by Varshni's relationship, $E_g(T)=2.9514\;eV-(7.24{\times}10^{-4}\;eV/K)T2/(T＋489K)$. After the as-grown $ZnIn_2S_4$ single-crystal thin films was annealed in Zn-, S-, and In-atmospheres, the origin-of-point defects of the $ZnIn_2S_4$ single-crystal thin films were investigated via the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_S$, $Zn_{int}$, and $S_{int}$ obtained from the PL measurements were classified as donor or acceptor types. Additionally, it was concluded that a heat treatment in an S-atmosphere converted $ZnIn_2S_4$ single crystal thin films into optical p-type films. Moreover, it was confirmed that In in $ZnIn_2S_4$/GaAs did not form a native defects, as In in $ZnIn_2S_4$ single-crystal thin films existed in the form of stable bonds.