• Polymer(Korea)
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• v.25 no.2
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• pp.254-262
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• 2001

Epoxy resin based upon the N,N'-diglycidylaniline which is widely used in optic, electronic and composite material. We modified this epoxy resin with poly(amic acid) (PAA) that is a precursor of polyimide. To improve the mechanical property we controlled PAA content and imidization ratio. PI-modified epoxy blends were prepared for the formation of IPN structure. The possible reaction in the epoxy resin/PAA blends were investigated by FT-IR and inherent viscosity techniques. Thermal properties are measured by TGA, DSC, and TMA. Mechanical properties are measured by UTM and impact test machine. Morphology is investigated by SEM. Thermal stability improved with increasing the content of PAA in blends. As the content of PAA increases in blend, the glass transition temperature and thermal expansion coefficient decreases. Increasing impact strengths in J/m in the range of 920∼2412 were observed in blends. The PAA segment may act as a toughening agent in the epoxy networks, thus contributing the impact strength improvement of the blends.

• Composites Research
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• v.21 no.1
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• pp.16-21
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• 2008

The cure behavior of epoxy resin with a conventional amide-type hardener(HD) was investigated in the presence of castor oil(CO), cashew nut shell liquid(CNSL) and CNSL-formaldehyde resin(CFR) by using a dynamic differential scanning calorimetry(DSC). The activation energy of curing reaction was also calculated based on the non-isothermal DSC thermograms at various heating rates. An one-stage curing was noted in the case of epoxy resin filled with CO, while the epoxy resin with CNSL and CFR showed a two-stage curing process. A competitive cure reaction was noted for the epoxy resin/CNSL(or CFR)/HD blends. In the absence of HD, the CFR showed lower values of curing enthalpy than that of CNSL. The activation energy of epoxy resin curing increased with increasing the CNSL and CFR loading.

• Advances in nano research
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• v.14 no.5
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• pp.443-450
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• 2023

Carbon nanotubes (CNTs) have received increased interest in reinforcing research for polymer matrix composites due to their exceptional mechanical characteristics. Its high surface area/volume ratio and aspect ratio enable polymer-based composites to make the most of its features. This study focuses on the experimental tensile testing and fabrication of carbon nanotube reinforced composite (CNTRC) beams, exploring various micromechanical models. By examining the performance of these models alongside experimental results, the research aims to better understand and optimize the mechanical properties of CNTRC materials. Tensile properties of neat epoxy and 0.3%; 0.4% and 0.5% by CNT reinforced laminated single layer (0°/90°) carbon fiber composite beams were investigated. The composite plates were produced in accordance with ASTM D7264 standard. The tensile test was performed in order to see the mechanical properties of the composite beams. The results showed that the optimum amount of CNT was 0.3% based on the tensile capacity. The capacity was significantly reduced when 0.4% CNT was utilized. Moreover, the experimental results are compared with Finite Element Models using ABAQUS. Hashin Failure Criteria was utilized to predict the tensile capacity. Good conformance was observed between experimental and numerical models. More importantly is that Young' Moduli of the specimens is compared with the prediction Halpin-Tsai and Mixture-Rule. Although Halpin-Tsai can accurately predict the Young's Moduli of the specimens, the accuracy of Mixture-Rule was significantly low.

• Structural Engineering and Mechanics
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• v.74 no.4
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• pp.515-520
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• 2020

In the modern era, the world is facing unprecedented challenges in form of environmental pollution and international agencies are forcing scientists and materialists to look for green materials and structures to counter this problem. Composites based on renewable sources like plant based fibres, vegetable fibres are finding increasing use in interior components of automobile vehicles, aircraft, and building construction. In the present study, jute and flax fibre based composites were developed and tested for assessing their suitability for possible applications in interior cabin and parts of automobile and aerospace vehicles. Matrix system involves epoxy as resin and fibre weight fractions used were 45% and 55% respectively. Composites samples were prepared as per American society for testing and materials (ASTM) standard and were tested for individual fiber tensile strength, composite tensile strength, and flexural strength to analyse its behavior under various loading conditions. The results revealed that the Jute fibre composites possess enhanced mechanical properties over Flax fibre composites.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.835-842
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• 2002

In this paper, static and fatigue bending strengths and failure mechanisms of CFRP (carbon fiber reinforced plastics) laminates having impact damages have been evaluated. Composite laminates used for this experiment are CF/EPOXY orthotropy laminated plates, which have two-interfaces $[0^0_ 4/90^0_4]_{ sym}$. A steel ball launched by the air gun collides against CFRP laminates to generate impact damages. The damage growth during bending fatigue test is observed by the scanning acoustic microscope (SAM) and also, the fracture surfaces were observed by using the SEM (scanning electron microscope). In the case of impacted-side compression, fracture is propagated from the transverse crack generated near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-B delamination in the case of impacted-side tension. Eventually, failure mechanisms have been confirmed based on the observed delamination areas and fracture surfaces.

• Carbon letters
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• v.15 no.4
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• pp.255-261
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• 2014

Multi-walled carbon nanotube reinforced epoxy composites were fabricated using shear mixing and sonication. The mechanical, viscoelastic, thermal, and electrical properties of the fabricated specimens were measured and evaluated. From the images and the results of the measurements of tensile strengths, the specimens having 0.6 wt% nanotube content showed better dispersion and higher strength than those of the other specimens. The Young's moduli of the specimens increased as the nanotube filler content was increased in the matrix. As the concentrations of nanotubes filler were increased in the composite specimens, their storage and loss moduli also tended to increase. The specimen having a nanotube filler content of 0.6 wt% showed higher thermal conductivity than that of the other specimens. On the other hand, in the measurement of thermal expansion, specimens having 0.4 and 0.6 wt% filler contents showed a lower value than that of the other specimens. The electrical conductivities also increased with increasing content of nanotube filler. Based on the measured and evaluated properties of the composites, it is believed that the simple and efficient fabrication process used in this study was sufficient to obtain improved properties in the specimens.

• Advances in nano research
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• v.14 no.3
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• pp.261-271
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• 2023

The present study follows three main goals. First, an analytical solution with high accuracy is developed to assess the effects of embedding pre-strained shape memory alloy (SMA) wires on the critical buckling temperatures of rectangular sandwich plates made of soft core and graphite fiber/epoxy (GF/EP) face sheets based on piecewise low-order shear deformation theory (PLSDT) using Brinson's model. As the second goal, this study compares the effects of SMAs on the thermal buckling of sandwich plates with those of carbon nanotubes (CNTs). The glass transition temperature is considered as a limiting factor. For each material, the effective ranges of operating temperature and thickness ratio are determined for real situations. The results indicate that depending on the geometric parameters and thermal conditions, one of the SMAs and CNTs may outperform the other. The third purpose is to study the thermal buckling of sandwich plates with advanced hybrid SMA/CNT/GF/EP composite face sheets. It is shown that in some circumstances, the co-incorporation of SMAs and CNTs leads to an astonishing enhancement in the critical buckling temperatures of sandwich plates.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.57-60
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• 2002

The stiffness model has been proposed to predict elastic constants of twisted yarn composites. The model is based upon the unit cell structure, the coordinate transformation, and the volume averaging of compliance constants for constituent materials. For the correlation of analytic results with experiments, composite samples of various yarn twist angle were tested. The samples were fabricated by the RTM process using glass yarns and epoxy resin. The correlations of elastic constants showed relatively good agreements. The model provides the predictions of the three-dimensional engineering constants, which are valuable input data for the analytic characterization of textile composites made of twisted yarn.

• Composites Research
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• v.12 no.4
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• pp.1-7
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• 1999

Fatigue life prediction of matrix dominated composite laminates, which have a nonlinear stress/strain response, was studied analytically and experimentally. A stress function describing the relation of initial fatigue modulus and elastic modulus was used in order to consider the material nonlinearty. New modified fatigue life prediction equation was suggested based on the fatigue modulus and reference modulus concept as a function of applied stress. The prediction was verified by torsional fatigue test using crossply carbon/epoxy laminate tubes. It was shown that the proposed equation has wide applicability and good agreement with experimental data.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.04a
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• pp.1-6
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• 2001

In this paper, edge delaminations in cracked composite plates are analytically investigated. A theoretical model based upon a sub-laminate approach is used to determine the strain energy release rate, $G^{ed}$, in [$\pm$$\theta_m$/$90_n$]$_s$ carbon/epoxy laminates loaded in tension. The analysis provides closed-form expressions for the reduced stiffness due to edge delamination and matrix cracking and the total energy release rate. The parameters controlling the laminate behaviour are identified. It is shown that the available energy for edge delamination is increased notably due to transverse ply cracking. Also thermal stresses increase substantially the strain energy release rate and this effect is magnified by the presence of matrix cracking. Prediction for the edge delamination onset strain is presented and compared with experimental data. The analysis could be applied to ceramic matrix composite laminates where similar mechanisms develop, but further experimental evidence is required.