Abstracts:Based on the three-dimensional elasticity theory, the investigation of the free vibration response of a carbon nanotube-reinforced cylindrical panel resting in elastic foundation in thermal environments is presented. The response of the elastic medium is formulated by the Winkler/Pasternak model. The cylindrical panel has been reinforced by carbon nanotube in the radial direction and the material properties are temperature dependent and estimated by the extended rule of mixture. Dynamic Young’s modulus of single-walled carbon nanotubes can be expressed a function of loading rate and environmental temperature. Differential quadrature method is being utilized and natural frequencies of cylindrical panel are obtained. An accuracy of the present solution is confirmed by comparing with some available results in the article. A detailed numerical study is conducted to examine the effects of temperature rise, carbon nanotube volume fraction, elastic foundations and the geometrical parameters on the deflection of the cylindrical panels.

Abstracts:With growing inclination towards the eco-friendly technology, natural fiber based polymer composite materials have been gaining a lot of momentum nowadays. The present review discusses the much research that has been carried out in the area of the epoxy-based composites reinforced with natural fibers. Influence of the various factors like the fiber content, fiber geometry, fiber size, surface treatment technique, and coupling agent on different properties like mechanical, thermal, behavior towards water absorption and others have been presented. It can be inferred that there is a need and scope for improvement of the surface properties of natural fiber using various methods like physical and chemical treatments, addition of coupling agents, etc. for the manufacturing of the composites having desired properties. These techniques not only modify surface morphology, but also improve other processing parameters like the hydrophilic character of fiber (which is desirable to be low), and hence improve several characteristics such as mechanical properties, thermal stability, water absorption and other considerations of the composites.

Abstracts:Homogenization is very efficient tool in modeling of complex phenomena in heterogeneous media due to different length scales between the characteristic length of the microstructural features and the actual macroscale dimensions. This is particularly important when dealing with voided composite structures due to the high degree of microstructural irregularity. One of the challenges in designing polymeric porous or voided structures is the absence of accurate and robust viscoelastic homogenization technique that takes into account the microstructural details. Another challenge underlies in constructing the microstructure for numerical homogenization. This work proposes reduced 3D reconstruction procedure of voided composite structures based on statistical considerations and granular mechanics. Voids’ diameters and fractions of the actual microstructure were extracted with a deterministic locally adaptive thresholding technique. The diameters were categorized with Freedman-Diaconis method but preserving the overall voids’ fractions. The simulation box was then created from the reduced voids’ diameters and fractions with granular mechanics. Numerical experiments were conducted with periodic boundary conditions to the walls of the simulation box. Voided structures of Acrylonitrile Butadiene Styrene (ABS) were fabricated with physical foaming agent and tested for creep compliance to validate the proposed procedure. The agreement with experimental results for creep compliance is very good with maximum error of 8.62%. The contribution of the procedure is attributed to the simplicity and accuracy in developing representative voided structures from SEM images which otherwise need to be extracted from tedious processes like X-ray microtomography reconstruction.

Abstracts:It is the first time to report the effects of graphene oxide (GO) coating on the mechanical properties of short glass fiber (SGF) reinforced polymer composites. GO-coated SGF reinforced polyethersulphone (PES) composites are manufactured using extrusion compounding and injection molding techniques. The micro-structures and morphologies of GO and GO-coated SGFs are investigated using scanning electron microscopy, small-angle X-ray scattering, atomic force microscope and Fourier transform infrared techniques. Then, the tensile and flexural properties of the GO-coated SGF/PES composites are systematically studied taking into account the effect of GO coating content. It is observed that both the tensile and flexural strengths are effectively enhanced by the GO coating on the SGF surfaces. This observation is mainly attributed to the enhanced interfacial adhesion between SGFs and PES due to the GO coating. Moreover, the tensile and flexural moduli are also improved by the addition of GO due to the fact that GO has a much higher modulus than the PES matrix.

Abstracts:In this paper, microwave radiation, a fast and cost-effective industrial surface pretreatment method without chemicals, was employed to pretreat T300 carbon fibres and improve the carbon fibres/matrix interfacial properties. The microwave pretreatment mechanism on carbon fibres was studied in an experiment divided microwave treated carbon fibres into a microwave radiation section and a pure current section. The polarization current in the carbon fibre induced by microwave radiation helped microwave effects interact on the morphology, compositions, and structure of carbon fibres. Carbon fibres pretreated with short time microwave radiation had an increased thermodynamic work of adhesion and the interfacial shear strength, indicating microwave radiation pretreatment of carbon fibre promises to be an effective method of fiber treatment.

Abstracts:The flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with internal glass fiber-reinforced polymer (GFRP) bars was experimentally investigated. For this, large-sized beams with four different reinforcement ratios (ρ = 0.53–1.71%) were fabricated and tested. All test beams exhibited very stiff load-deflection response beyond the first cracking point and satisfied the crack width criteria of ACI 440.1R and CAN/CSA S806 at serviceability limit state and deformability requirement by CAN/CSA-S6. Higher reinforcement ratio resulted in better flexural performances such as higher post-cracking stiffness, maximum moment capacity, ductility, and deformability. The effective moment of inertia equation from the current ACI 440.1R code, which is based on Bischoff’s model, significantly overestimated the service deflections of UHPFRC beams with GFRP bars because of its inappropriate first cracking prediction and moment of inertia equation at cracked section. Therefore, alternative equation for predicting first cracking moment and moment of inertia of cracked section in strain-hardening zone for UHPFRC was suggested, and it was verified through comparison with the measured service deflections.

Abstracts:In this study, the Poly(vinyl alcohol)(PVA)/wood powder composite was prepared through combining the novel technologies of solid-state shear milling (S³M) and thermal processing of PVA, which provided a large-scale and non-solvent way to efficiently utilize the abundant biomass materials. The results showed that S³M can significantly promote pulverization, dispersion, mechanical activation, and interfacial compatibility of the components, endowing the materials with better processability and mechanical performances. The XRD and FTIR results showed that with the increasing of milling cycles, the hydrogen bonds of PVA molecules were partially destroyed, leading to the formation of looser crystalline structure and lower crystalline degree, while the hydrogen bonding between PVA and wood powder was strengthened. Combining with thermal processing technology of PVA, the composite treated by S³M had a good processability and mechanical properties. DSC curves revealed that the melting temperature of PVA/wood powder (70 wt/30 wt) composite decreased to 123 °C, providing a quite wide thermal processing window for composite. High-pressure Capillary rheology analysis showed that the shear viscosity of the composite decreased with the increasing milling cycles. Finally, the composites exhibited significant improvements in mechanical properties. The tensile strength increased from 16.6 MPa to 22.5 MPa, and the elongation at break increased from 32.0% to 120.5%, respectively.

Abstracts:We demonstrate ZnO nanowire arrays (NWAs) and ZnO NWAs/graphene composites grown on ZnO seed layers on Cu substrate via a hydrothermal method and graphene film layer chemically synthesized at low pressure chemical vapor deposition. In the case of the Cu substrate covered with graphene layer, the uniform and vertically aligned ZnO NWAs/graphene composites with the average diameter of 80 nm grown on ZnO seed layers were obtained and growth mechanism of that has been proposed. The photoluminescence (PL) spectra of ZnO NWAs/graphene composites shows enhanced intensity of UV emission and decreased intensity of visible emission. In addition, field emission measurements reveal that the ZnO NWAs/graphene composites have a lower turn-on field of 1.74 V/μm and higher field enhancement factor of 12130 in comparison to that of graphene film layer and ZnO NWAs, which demonstrate ZnO NWAs/graphene composites are characteristic of having excellent emitting behavior in field emission technology.

Abstracts:Polyacrylonitrile-based carbon fibers are cryogenically conditioned both through a low cooling rate and a quench rate to explore the effects of cryogenic treatments on properties and micro-structures of carbon fibers. The internal structure, tensile properties and surface morphologies of the fiber are investigated. Increase in crystallinity and tighter packing of molecules of the fiber after the cryogenic treatments are observed regardless the cooling rate. After slow cooling cryogenic treatment, the inter-planar distance increases in the fiber axial direction and decreases in the fiber radial direction, resulting in 3% shrinkage of fiber diameter and extension in fiber axial direction. Scanning electron microscopy and atomic force microscopy analysis show slightly wider and deeper rill-like folds and 41% roughness increase for the fiber surfaces, leading to an increase in interfacial shear strength between the fiber and epoxy by 30.2%. In contrast, after sharp cooling cryogenic treatment, no obvious change is detected in inter-planar distance, fiber diameter, surface morphology and interfacial shear strength with epoxy. The bimodal additive Weibull distributions of tensile strengths for the cryogenic treated fibers show an increase of the bimodality parameter α and a decrease in scale parameter σ indicating higher probability of extrinsic defects but no significant mechanical degradation of the fiber after cryogenic treatments.

Abstracts:A novel continuous segregated structure was constructed in polypropylene (PP)/carbon black (CB) composites, to improve the electrical conductive performance and achieve a balance of the electrical conductivity and mechanical properties. Compared with traditional segregated structures reported in literature, PP matrix maintained a continuous structure instead of being separated completely by the electrical conductive fillers and CB particles formed a thorough conductive network in the continuous segregated PP/CB composites. A percolation threshold as low as 0.37 vol%, which is significantly lower than the percolation threshold of melt compounded PP/CB composites (2.75 vol%) and PP/polystyrene (PS)/CB composites (3.23 vol%) with a double percolation structure, was obtained because of the formation of the two-dimensional conductive network of CB particles. The mechanical performance tests showed that the tensile modulus, strength and elongation of break could be maintained well at CB contents around the percolation threshold. That is, with this novel continuous segregated structure, a balance of strength, toughness and electrical conductivity property can be achieved in conductive polymer composites.