Totally found 1005 items.

  • [期刊] Robust and repairable bulk polymeric coatings with continuous superhydrophobicity for design control and underwater display
    Functionalized polymeric materials with superhydrophobicity are considered as promising candidates for advanced and smart materials. Herein, a bulk superhydrophobic polymeric coating (BSPC) integrating robustness with repairability for design control and underwater display was fabricated based on the combination of covalently cross-linking epoxy acrylate resin (EAR) and hierarchical precipitated silica particle (PSP). By optimizing the ratio of polymer/particle (10: 4), the BSPC exhibited solid mechanical strength while facing various aggressive stress (>200 cycles). Thanks to the continuous superhydrophobicity constructed by hierarchical topography in the polymer skeleton, the BSPC was demonstrated enticing repairable behavior by polish (>40 cycles). More importantly, the regenerative rough structures enabled the BSPC to achieved design control sequentially via the shedding of the surface layer. Simultaneously, based on the underwater light-reflection, the underwater display was successfully realized on the designed BSPC, which may broaden the application fields of superhydrophobic materials. Additionally, the BSPC presented self-cleaning, anti-corrosion (pH in 1/14), anti-boiling (100 degrees C) and anti-freezing (0 degrees C) performances. Our findings conceivably propose a feasible strategy to fabricate versatile superhydrophobic polymeric materials with continuous, repairable and designable features for advanced and smart fields.
  • [期刊] Investigating the effects of liquid-plasma treatment on tensile strength of coir fibers and interfacial fiber-matrix adhesion of composites
    The liquid-plasma treatment based on microwave plasma in the liquid was used to treat coir fiber in this study. The effects of such treatment on tensile properties of coir fiber and its compatibility with the epoxy matrix were investigated. Water and sodium bicarbonate (NaHCO3) solution was used as a medium in this treatment. Tensile properties and interfacial shear strength (IFSS) between coir fiber and epoxy resin were determined with single fiber tensile and pull-out tests respectively. Fourier transform infrared spectroscopy, scanning electron microscope and X-ray diffraction were used to characterize the alteration of treated coir fibers. The results show that tensile strength of coir fibers slightly reduce after liquid-plasma treatment with both water and sodium bicarbonate medium except on 12 wt% sodium bicarbonate solution medium for 5 min exposure time. Meanwhile, the interfacial shear strength of coir fiber-epoxy matrix is obtained improvement after water and sodium bicarbonate medium treatment due to good interfacial adhesion between fiber and matrix which could be influenced by micropores on fiber surfaces leading to interlocking adhesion.
  • [期刊] Towards novel high-performance bio-composites: Polybenzoxazine-based matrix reinforced with Manicaria saccifera fabrics
    Due to the worldwide awareness about environmental issues, there is an increasing demand for the development of low cost and ecofriendly materials. In this work, natural fabrics of Manicaria saccifera (MS), a palm tree from the Americas, were used to prepare polybenzoxazine-based bio-composites. These materials were initially developed as bidirectional alkaline-treated fabrics impregnated with benzoxazine resins (prepregs) and then cured in a hot-press. The good compatibility between matrix and reinforcement was confirmed by scanning electron microscopy (SEM), which showed that alkaline treatment led to a more homogeneous fabric surface, achieving improved interfacial interaction. The dynamic mechanical analysis revealed elevated glass transition temperatures (>115 degrees C) and crosslinking degrees. The results of tensile and flexural tests showed high elastic modulus, with values around 2 GPa. Thermal analyses indicate the great flame retardant performance of these bio-based materials due to their high char yields and LOI values. Therefore, this study suggests the elevate potential of these highly bio-based composites, comprising more than 60% of natural matter, to be used in high-performance applications, especially where flame-retardancy is required, like construction, aerospace or automotive industries.
  • [期刊] Numerical modeling of interply adhesion in composite forming of viscous discontinuous thermoplastic prepregs
    "Quilted Stratum Process" (QSP (R)) is a new process in the category of thermoplastic composite forming with the objective to locally strengthen the composite parts by strategically stacking discontinuous UD/woven prepregs while maintaining the short cycle time of about 1 min. Interply adhesion arising due to polymer tack plays an important role in QSP (R) due to the presence of resin-rich layer at the ply-ply interface, inability to use blank holders for prepreg patches and high temperature of forming process where the resin is in melt state. Without modeling interply adhesion in the numerical simulation of their forming, plies delaminate unrealistically without any resistance which in turn results in incorrect final positions of the prepreg patches. Thus, a penalty based, semi-empirical contact model for interply adhesion has been developed and implemented in the industrial finite element code of Altair RADIOSS (TM). This model allows sliding of plies over long distance while providing a finite adhesive strength before delamination. It requires minimal characterization for which a measurement method is proposed. The usage of this model in a full scale numerical simulation showed that the final ply positions were predicted with a much better accuracy. Also, the predictions of fibre orientations within individual plies are in good agreement with the experimental observations.
  • [期刊] Damage behaviors of unidirectional CFRP in orthogonal cutting: A comparison between single- and multiple-pass strategies
    Carbon Fibre Reinforced Plastics/Polymer (CFRP) composites has experienced a rapid revolution, requiring the accurately controllable machining technology. Although efforts have been paid on CFRP machining, most of them focused on the single-pass orthogonal cutting where the perfect unprocessed surfaces were employed as the initial state. The reality is however the multiple-pass cutting with the progressive cut depths has been widely used in the industries, where the influence of the defects generated in the previous passes on the following cuts can not be ignored. To fill this gap, this paper investigated the damage behaviors of unidirectional CFRP in orthogonal cutting with the special emphasis on the difference between the single- and the multiple-pass strategies. The good agreement were found between the experimental and simulation results, where the maximal relative errors were separately 10.1%, 9.2%, and 8% for fibre pull-out depth, fibre-matrix debonding depth and cutting forces. Further discussion based on the model can draw the conclusion that, the employment of the multiple-pass cutting strategy can improve the fibre breakage length by 40%, the fibre pull-out depth by 63%, and the fibre-matrix interface debonding by 25%. This work is anticipated to not only open a new avenue to provoke more in-depth thoughts of CFPR behaviors in cutting but also to provide the practical guidance for industrial CFRP high-quality machining.
  • [期刊] CNT-reinforced iron and titanium nanocomposites: Strength and deformation mechanisms
    The mechanical reinforcement of embedding a carbon nanotube inside metals with different crystal structures (BCC-Fe and HCP-Ti) is investigated using molecular dynamics simulations. Two metallic elements were chosen representing different crystal structures, based on the foreseeable technological benefits of improving the strength of these widely used metals while reducing their weight. Tensile and compressive loadings are applied to CNT-Fe and CNT-Ti nanocomposites which are modeled by inserting a (6,6) CNT into a single-crystal rectangular prism. Two limit boundary conditions are applied to the embedded CNT: (i) loading applied only to the metal matrix and (ii) loading applied to both the metal matrix and the embedded CNT. Curves of energy vs strain and stress vs strain are presented and the mechanical properties are calculated for both situations. Additionally, the mechanical behavior and buckling of the encapsulated carbon nanotube as a result of compression loading applied to the metal nanocomposites is also studied. Lastly, an analysis of the influence of the embedded CNT in the deformation mechanisms of the nanocomposites is presented.
  • [期刊] A stable high-performance isotropic electrorheological elastomer towards controllable and reversible circular motion
    In this paper, two kinds of isotropic giant electrorheological elastomers (GERE) were prepared with urea-coated barium titanyl oxalate nanoparticles as dielectric particles filler, poly (dimethyl siloxane) (PDMS) as an elastic matrix and silicone oil as a plasticizer. Such GEREs are far superior to other isotropic and even anisotropic electrorheological elastomers (EREs), showing excellent electrorheological (ER) performance. The theoretic mechanism in elastomers prepared by us should be explained by saturation surface polarization or orientational polarization model. More interestingly, the storage modulus increment (Delta G') of GEREs displays curvilinear dependence on the electric field due to poor particle mobility and different mobility under different electric fields, rather than a predicted linear variation. After testing their viscoelastic and dielectric properties and microstructures, we found that too high of the powder content leads to the serious agglomeration of particles and the performance degradation of the elastomer. An incorporation of silicone oil improved the dispersion state and wettability between the particles and matrix. At the same time, silicone oil reduced the hardness of the matrix and made the particles align more easily in the PDMS matrix. Lower initial modulus and higher field-induced modulus make GEREs containing silicone oil have ultrahigh storage modulus sensitivity, in which the best-performing sample achieved a storage modulus change exceeding 400 kPa and attained a maximum relative ER effect of 3280% at 3 kV/mm. Finally, the GERE was used to reversibly control the amplitude of circular motion within seconds by varying electric fields, revealing broad potential application in vibration control.
  • [期刊] Synergy effect between quaternary phosphonium ionic liquid and ammonium polyphosphate toward flame retardant PLA with improved toughness
    The development of poly(lactic acid) (PLA) composites having flame retardancy, tensile toughness and transparency is the state-of-the-art, which requires meticulous selection and combination of additives. To achieve this goal, an ionic liquid (IL) tetrabutylphosphonium tetrafluoroborate is synthesized and used as a synergist for ammonium polyphosphate (APP). Due to the high synergistic effect between them, only 1.5 wt% IL and 1.5 wt% APP (total amount of 3 wt%) can endow PLA with fire safety, i.e. limiting oxygen index (LOI) of 27.2, UL 94 V-0 rating and low heat release rate of 290 kW m(-2). Besides, the elongation at break of PLA containing 3 wt% IL/ APP increases from 8.5% of PLA to 204.6%. Meanwhile, the incorporation of IL/APP has tiny impact on the transparency of PLA. The PLA/IL/APP possessing toughness and flame retardancy shows great potentials in the fields of packaging, automotive and electronic and electric industry in the future.
  • [期刊] Numerical simulation of the tensile behavior of FRCM strengthening systems
    The direct tensile test is one of the experimental procedures used for the characterization of Fiber Reinforced Cementitious Matrix (FRCM) materials. From this test generally emerge the main phenomena characterizing the tensile response of FRCM: cracking of the matrix and de-bonding at the reinforcement-matrix interface. These phenomena, that in some cases are quite difficult to experimentally monitor and understand, particularly influence the performance of FRCM as strengthening systems. In this paper the authors present a simple numerical modeling approach able to simulate the tensile response of FRCM by reproducing the occurrence of both the cracking of the matrix and the de-bonding at the reinforcement-matrix interface. The numerical analyses reported in the paper show the reliability of the proposed approach and, in particular, its role as support tool for understanding the influence of local failure phenomena on the global tensile response of FRCM systems.
  • [期刊] Harnessing the ductility of polylactic acid/ halloysite nanocomposites by synergistic effects of impact modifier and plasticiser
    This study explores the efficacy of different additives for tuning ductility of polylactic acid (PLA) composites without significantly affecting their mechanical and thermal properties. Selective additives with unique characteristics, namely an impact modifier (lotader AX8900), a plasticiser (triethyl citrate- TEC), and a reinforcement (halloysite nanotubes-HNT) were extruded with PLA in different mass ratios, and resulting composites were evaluated for rheological, mechanical and thermomechanical characteristics. The thermomechanical analysis showed that PLA/HNT nanocomposites had 20 times higher storage modulus after rubbery stage, indicating excellent interaction of PLA/HNT. Addition of lotader in PLA/HNT composites reduced the crystallinity to 2% from 21% without affecting the glass transition (T-g) temperature. In contrast, addition of TEC yielded just the opposite effect. Lotader, individually and in combination with TEC, improved the elongation at break by 14 and 18 times, respectively. The addition of HNT in presence of lotader and TEC also improved the elongation by 19 times. However, lotader and TEC worked synergistically to improve the most sought-after characteristic of PLA, i. e., ductility while maintaining the similar tensile properties.