• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.633-637
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• 2023

Recently, with the development of the smart device market, the integration of high-functional devices has increased the heat density, causing overload of the device, and resulting in various problems such as shortened lifespan, performance degradation, and failure. Therefore, research on heat dissipation materials is being actively conducted to realize next-generation electronic products. The heat dissipation material is characterized in that it is easy to dissipate heat due to its high thermal conductivity and minimizes leakage current flowing through the heat dissipation material due to its low electrical conductivity. In this study, flower-shaped Al₂O₃ and BN composites were engineered with a simple hydrothermal synthesis approach, and their thermal conductivity characteristics were compared and evaluated for each synthesis condition for the application to a heat dissipation material. Spherical BN and flower-shaped Al₂O₃ were easily obtained, and SEM/EDS analyses confirmed the uniform presence of BN between the Al₂O₃, and it can be expected that these shapes can affect the thermal conductivity.

• Elastomers and Composites
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• v.56 no.4
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• pp.234-242
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• 2021

The demand for truck bus radial (TBR) tires with enhanced fuel efficiency and wear resistance have grown in recent years. In addition, as the issue of particulate matter and air pollution increases, efforts are being made to reduce the generation of particulate matter. In this study, the properties of epoxidized natural rubber (ENR) containing a silica-friendly functional group were evaluated by considering it as a base rubber and varying the silica ratio in this binary filler system. The results showed that the wear resistance of the NR/BR blend compound decreased as the silica ratio increased. In contrast, the ENR/BR blend compound exhibited an increase in wear resistance as the silica ratio was increased. In particular, the ENR-50/BR blend compound showed the best wear resistance due to the presence of several epoxide groups. Furthermore, we observed that for tan 𝛿 at 60℃, higher epoxide content resulted in the higher T_g of the rubber, indicating a higher tan 𝛿 at 60℃. On the other hand, it was confirmed that increasing the silica ratio decreased the value of tan 𝛿 at 60℃ in all compounds. In addition, we measured the amount of wear particulate matters generated from the compound wear. These measurements confirmed that in the binary filler system, regardless of the filler type, the quantity of the generated wear particulate matters as the filler-rubber interaction increased. In conclusion, the silica filled ENR/BR blend compound exhibited the lowest generation of wear particulate matters.

• Elastomers and Composites
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• v.56 no.4
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• pp.243-249
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• 2021

The demand for truck bus radial (TBR) tires with enhanced fuel efficiency and wear resistance have grown in recent years. In addition, as the issue of particulate matter and air pollution increases, efforts are being made to reduce the generation of particulate matter. In this study, we investigated the effect of varying the content of butadiene rubber (BR) on the properties of the rubber compounds and the amount of particulate matter in the TBR tire tread compound. Furthermore, we utilized carbon black in the NR/BR blend compounds owing to its excellent compatibility, and we used silica in the ENR-25/BR blend compounds because it can interact chemically with epoxide groups. The NR/BR blend compounds and the ENR-25/BR blend compounds were evaluated by varying their BR content between 20 phr and 30 phr. The results showed that the ENR-25/BR blend compounds had superior wear resistance than the NR/BR blend compounds. This was caused by the interaction between silica and ENR. In addition, it was confirmed that the increased wear resistance as the BR content increased. Furthermore, compared to the NR/BR blend compounds, ENR-25/BR blend compounds exhibited a lower tan 𝛿 value at 60℃ because silica was used as filler. This indicates a higher fuel efficiency. The measurement results for wear particulate matter showed that as increasing the BR content resulted in generation of less wear particulate matter. This was caused by the increased wear resistance. Moreover, the ENR-25/BR blend compounds with excellent filler-rubber interaction exhibited lower quantities of generated wear particulate matters as compared to the NR/BR blend compounds.

• Composites Research
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• v.36 no.5
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• pp.377-382
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• 2023

To enhance the performance of graphene-based devices, it is of great importance to better understand the interfacial interaction of graphene with its underlying substrates. In this study, the adhesion energy of monolayer graphene placed on dielectric substrates was characterized using mode I fracture tests. Large-area monolayer graphene was synthesized on copper foil using chemical vapor deposition (CVD) with methane and hydrogen. The synthesized graphene was placed on target dielectric substrates using polymer-assisted wet transfer technique. The monolayer graphene placed on a substrate was mechanically delaminated from the dielectric substrate by mode I fracture tests using double cantilever beam configuration. The obtained force-displacement curves were analyzed to estimate the adhesion energies, showing 1.13 ± 0.12 J/m² for silicon dioxide and 2.90 ± 0.08 J/m² for silicon nitride. This work provides the quantitative measurement of the interfacial interactions of CVD-grown graphene with dielectric substrates.

• Composites Research
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• v.20 no.5
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• pp.64-69
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• 2007

Matrix dominant properties of composites are largely degraded under harmful environments such as temperature and humidity. Therefore we should consider the harmful environmental factors in the design of an UAV integral fuel tank subjected to high temperature and high humidity. The harmful environment experiment was performed for carbon/epoxy composites made of a unidirectional prepreg USN175B, and a plain woven fabric prepreg WSN3. The immersion experiment was performed under $90^{\circ}C$. The specimens were tested when the weight gam of specimen was saturated. The specimens were tested under $74^{\circ}C$ to obtain tensile and inplane shear properties. The results showed that the matrix dominant properties were extremely degraded by hygrothermal environment. To consider the variability of load, the anti-optimization method was applied. By using this method, the worst load case was found by comparing the load convex model and stability boundary. The stability boundary was obtained by analysis of the integral wing fuel tank of UAV using degraded properties. To do this, it was known that the worst load case of the integral wing fuel tank was the hovering mode load case.

• Journal of the Korea Institute of Building Construction
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• v.24 no.2
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• pp.203-213
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• 2024

This study delves into the mechanical properties of fiber-reinforced cement composites(FRCC) concerning the dispersion method of multi-walled carbon nanotubes(MWCNTs). MWCNTs find utility in industrial applications, particularly in magnetic sensing and crack detection, owing to their diverse properties including heat resistance and chemical stability. However, current research endeavors are increasingly directed towards leveraging the electrical properties of MWCNTs for self-sensing and smart sensor development. Notably, achieving uniform dispersion of MWCNTs poses a challenge due to variations in researchers' skills and equipment, with excessive dispersion potentially leading to deterioration in mechanical performance. To address these challenges, this study employs ultrasonic dispersion for a defined duration along with PCE surfactant, known for its efficacy in dispersion. Test specimens of FRCC are prepared and subjected to strength, drawing, and direct tensile tests to evaluate their mechanical properties. Additionally, the influence of MWCNT dispersion efficiency on the enhancement of FRCC mechanical performance is scrutinized across different dispersion methods.

• Smart Structures and Systems
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• v.19 no.2
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• pp.127-136
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• 2017

Fiber reinforced polymer (FRP) has received widespread attention in the field of civil engineering because of its superior durability and corrosion resistance. This article presents the damage mechanisms of a novelty composite called carbon nanofiber modified flax fiber polymer (CNF-modified FFRP). The ability of acoustic emission (AE) to detect damage evolution for different configurations of specimens under uniaxial tension was examined, and some useful AE characteristic parameters were obtained. Test results shows that the mechanical properties of modified composites are associated with the CNF content and the evenness of CNF dispersed in the epoxy matrix. Various damage mechanisms was established by means of scanning electron microscope images. The fuzzy c-means clustering were proposed to classify AE events into groups representing different generation mechanisms. The classifiers are constructed using the traditional AE features -- six parameters from each burst. Amplitude and peak-frequency were selected as the best cluster-definition features from these AE parameters. After comprehensive comparison, a correlation between these AE events classes and the damage mechanisms observed was proposed.

• Smart Structures and Systems
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• v.16 no.6
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• pp.1023-1047
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• 2015

In this study, the optimal location of the MR fluid segments in a partially treated laminated composite sandwich plate has been identified to maximize the natural frequencies and the loss factors. The finite element formulation is used to derive the governing differential equations of motion for a partially treated laminated composite sandwich plate embedded with MR fluid and rubber material as the core layer and laminated composite plate as the face layers. An optimization problem is formulated and solved by combining finite element analysis (FEA) and genetic algorithm (GA) to obtain the optimal locations to yield maximum natural frequency and loss factor corresponding to first five modes of flexural vibration of the sandwich plate with various combinations of weighting factors under various boundary conditions. The proposed methodology is validated by comparing the natural frequencies evaluated at optimal locations of MR fluid pockets identified through GA coupled with FEA and the experimental measurements. The converged results suggest that the optimal location of MR fluid pockets is strongly influenced not only by the boundary conditions and modes of vibrations but also by the objectives of maximization of natural frequency and loss factors either individually or combined. The optimal layout could be useful to apply the MR fluid pockets at critical components of large structure to realize more efficient and compact vibration control mechanism with variable damping.

• Smart Structures and Systems
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• v.8 no.5
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• pp.471-486
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• 2011

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

• Smart Structures and Systems
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• v.26 no.2
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• pp.157-174
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• 2020

The guided wave technique is commonly used in structural health monitoring as the guided waves can propagate far in the structures without much energy loss. The guided waves are conventionally generated by the surface-mounted piezoelectric wafer active sensor (PWAS). However, there is still lack of understanding of the wave propagation in layered structures, especially in structures made of anisotropic materials such as carbon fiber reinforced polymer (CFRP) composites. In this paper, the Rayleigh-Lamb wave strain tuning curves in a PWAS-mounted unidirectional CFRP plate are analytically derived using the normal mode expansion (NME) method. The excitation frequency spectrum is then multiplied by the tuning curves to calculate the frequency response spectrum. The corresponding time domain responses are obtained through the inverse Fourier transform. The theoretical calculations are validated through finite element analysis and an experimental study. The PWAS responses under the free, debonded and bonded CFRP conditions are investigated and compared. The results demonstrate that the amplitude and travelling time of wave packet can be used to evaluate the CFRP bonding conditions. The method can work on a baseline-free manner.