Mechanical behavior of basalt and glass textile composites at high strain rates: A comparison

The aim of this paper is to study and compare the mechanical behavior of woven basalt and woven glass epoxy composites at high strain rates, in order to assess the possibility of replacing glass fiber composites with basalt fiber composites for aircraft secondary structures, such as radomes, fairings, wing tips, etc. Both composites were produced using the same epoxy matrix, the same manufacturing technique, and with comparable densities, fiber volume fractions, and static stiffnesses. Dynamic tensile and shear experiments were performed using a split Hopkinson tension bar, in addition to reference quasi-static experiments to compare both material behaviors over a wide range of strain rates. Normalized results with respect to the material density and fiber volume fraction showed that basalt epoxy composite had higher elastic stiffness, ultimate tensile strength, ultimate tensile strain, and absorbed energy in tension compared to glass epoxy composite. This suggests a promising potential in replacing glass fibers composites with basalt fiber composites in aircraft secondary structures and, more generally, components prone to impact. However, for the basalt epoxy composite, improvements in the fiber-matrix adhesion and in the manufacturing technique are still required to enhance their shear properties compared to glass fiber composites, and fully exploit the potential of basalt epoxy composites in aeronautical applications.     

Correlation between the a relaxation and the excess wing for polychlorinated biphenyls and glycerol

Data are presented for three glass formers, each having an excess wing in the low temperature dielectric loss spectra. Two polychlorinated biphenyls, whose α relaxations have equivalent temperature dependences, exhibit excess wings that are clearly different. Comparison of the spectra for glycerol at atmospheric pressure and at P=0.9 GPa reveals a different response of the α relaxation and the excess wing. These findings cannot be reconciled with the notion that the excess wing is an inherent part of the α relaxation. Interpretation of the spectra as a superposition of distinct α and β processes, however, is consistent with the observed behavior. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation and properties of polyimide/chopped carbon fiber composite foams

In this study, a series of reinforced polyimide (PI)/carbon fiber (CF) composite foams were fabricated through thermal foaming of polyester ammonium salt (PEAS) precursor powders. The PEAS precursor powders containing different contents of chopped CF were synthesized from benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride (BTDA) and 4,4′‐diaminodiphenyl ether (ODA). The effects of different CF loadings on foaming behavior of PEAS/CF composite precursor powders, final cellular morphology, and physical properties of PI composite foams were investigated. The results revealed that the chopped CF acted as nucleation agent in the foaming process. The dispersion of CF can be evaluated using digital microscope. It is interesting to find that the chopped CF were highly oriented along the direction of cell arrises. As a result, the mechanical properties of PI foams were significantly enhanced owing to the incorporation of chopped CF. Furthermore, the thermal stability of PI composite foams were also slightly improved owing to fine dispersion of CF. In addition, the PI/CF composite foam shows uniform cell size distribution and the best comprehensive physical properties as chopped CF loading at around 6 wt%. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamics of mobile ions: fitting of CKN frequency response data without an excess wing

Ion dynamics effects and the resulting dispersed frequency response of conducting materials have often been explained in the past by a combination of the Moynihan original modulus formalism (OMF) and the Ngai coupling model (NCM). These incorrect approaches and their inappropriate conclusions are replaced by alternate, Kohlrausch-related physically reasonable conductive-system fitting and interpretation models that are then used for the analysis of both limited-range and wide-range data for the supercooled liquid 0.4Ca(NO3)2*0.6KNO3 (CKN). Detailed analysis of the limited-range 342 K data at the electric modulus immittance level shows that OMF fitting leads to an excess wing and that more appropriate models fit the data well without such a wing. Further, although such models allow estimation of the bulk dipolar dielectric constant of the material, as well as one associated only with mobile charges, they lead to implausibly small estimates of the important Kohlrausch K1 model shape parameter, beta1, and lead to an inadequate determination of its characteristic relaxation time. Therefore, wide-range CKN data sets extending to nearly 1012 Hz for the temperatures 342, 350, 356, and 361 K were very well-fitted with a more detailed composite model but one still involving K1 response. All model parameters were well-determined with no excess wings; beta1 estimates were all much closer to the universal value of 1/3; and the estimated model parameters led to a Boson peak beyond 1012 Hz, to very large thermal activation energies, and to evidence that the mobile charge concentration reached a saturation value at about 356 K. Such results do not support assumptions about variable ion-ion correlation, a mainstay of the OMF and NCM approaches. Finally, it is shown that although excess wings can sometimes be eliminated by using just an appropriate bulk fitting model and series blocking-electrode capacitor, as shown for the present narrow-range data, adequate fitting of the present wide-range data sets over their full spans of as much as 13 decades required the addition of an additional series dispersive-response model to the composite model. This addition seems likely to be required to take adequate account of the presence of more than one species of mobile charge in CKN.     

Primary and secondary relaxations in supercooled eugenol and isoeugenol at ambient and elevated pressures: dependence on chemical microstructure

Dielectric loss spectra of two glass-forming isomers, eugenol and isoeugenol, measured at ambient and elevated pressures in the normal liquid, supercooled, and glassy states are presented. The isomeric chemical compounds studied differ only by the location of the double bond in the alkyl chain. Above the glass transition temperature T(g), the dielectric loss spectra of both isomers exhibit an excess wing on the high frequency flank of the loss peak of the alpha relaxation and an additional faster gamma process at the megahertz frequency range. By decreasing temperature below T(g) at ambient pressure or by elevating pressure above P(g), the glass transition pressure, at constant temperature, the excess wing of isoeugenol shifts to lower frequencies and is transformed into a secondary beta-loss peak, while in eugenol it becomes a shoulder. These spectral features enable the beta-relaxation time tau(beta) to be determined in the glassy state. These changes indicate that the excess wings in isoeugenol and eugenol are similar and both are secondary beta relaxations that are not resolved in the liquid state. While in both isoeugenol and eugenol the loss peak of the beta relaxation in the glassy state and the corresponding excess wing in the liquid state shifts to lower frequencies on elevating pressure, the locations of their gamma relaxation show little change with increasing pressure. The different pressure sensitivities of the excess wing and gamma relaxation are further demonstrated by the nearly perfect superposition of the alpha-loss peak together with excess wing from the data taken at ambient pressure and at elevated pressure (and higher temperature so as to have the same alpha-peak frequency), but not the gamma-loss peak in both isoeugenol and eugenol. On physical aging isoeugenol, the beta-loss peak shifts to lower frequencies, but not the gamma relaxation. Basing on these experimental facts, the faster gamma relaxation is a local intramolecular process involving a side group and the slower beta relaxation mimics the structural alpha relaxation in behavior, involves the entire molecule and satisfies the criteria for being the Johari-Goldstein beta relaxation. Analysis and interpretation of the spectra utilizing the coupling model further demonstrate that the excess wings seen in the equilibrium liquid states of these two isomers are their genuine Johari-Goldstein beta relaxation.     

Biomimetic Fabrication of Polymer Film with High Adhesive Superhydrophobicity by Duplicating Locust Wing Surface

Locust is a common flying insect. Locust wings were used as biomimetic templates to fabricate multi-functional polymer(polydimethylsiloxane, PDMS) films by soft lithography. The microstructure and wettability of the natural and artificial locust wing surfaces were investigated by means of a scanning electron microscope(SEM) and a video-based contact angle meter. The natural locust wing surface exhibits complicated hierarchical structures and high adhesive superhydrophobicity(contact angle 152°). The prepared polymer film faithfully reproduces the surface microstructures of the bio-template, and displays a good hydrophobicity and high adhesion(contact angle 144°). The complex wettability of the natural and artificial locust wing surfaces ascribes to the cooperative effect of hydrophobic composition and multi-dimensional rough microstructures. This work not only promotes our understanding of the wetting mechanism on bio-surfaces, but offers an inexpensive and effective approach for biomimetic fabrication of multi-functional interfacial materials.     

Study of the colloidal stability of concentrated bimodal magnetic fluids

In this paper, we describe an investigation of the stability and sedimentation behavior of moderately concentrated suspensions of extremely bimodal magnetite particles, including micro- (diameter 1450 nm) and nano- (diameter 8 nm) units. An original method is used, based on the determination of the time dependence of the inductance of a coil surrounding the suspensions. The method proves to be very useful for the determination of the volume fraction of magnetic material in the sensed volume. The observed changes in the resonant frequency of a parallel LC circuit demonstrate that the addition of the magnetite nanoparticles improves the stability and slows down the settling rate of the mixed suspensions. It is proposed that the observed behavior is the result of competition between two processes. One is the formation of a cloud of nanoparticles around the large magnetite units, by virtue of which the latter are maintained at distances beyond the range of DLVO and magnetic attractive interactions. At long times, these composite units will eventually sediment when some critical size is reached, as the small particles are progressively associated with the large ones. The second mechanism is mainly predominant at short times and is related to the higher viscosity of the dispersion medium (the nanoparticles dispersed in the base fluid) for higher nanoparticle concentrations. The stability of the suspensions is discussed in terms of the competition between the two mechanisms.     

Finite-element modeling of the heat mode of autoclave hardening of a three-layer panel

Results of finite-element modeling and experimental measurements of temperatures in the course of autoclave hardening of a three-layer panel of the wing of a T-50 aircraft, which is composed of upper and lower load-bearing panels made of carbon plastics and honeycomb from aluminum foil, are given. It is shown that the actual temperature values at various sections of the panel of wing differ from the theoretical ones by less than 90%.     

静电纺氧化锰复合碳纳米纤维柔性膜的电化学性能

采用一步法静电纺丝技术制备了具有超亲水特性的氧化锰/碳纳米纤维(MnO_x/CNFs)复合柔性膜电极材料,并通过X射线衍射、扫描电子显微镜和透射电子显微镜等对复合材料进行了表征.电化学性能测试结果表明,复合材料的电容性能优于单一材料,醋酸锰质量分数为40%时制得的复合纳米纤维电极(MC-4)在1 A/g电流密度下,于2 mol/L KOH电解液中的比电容高达1112.5 F/g,10 A/g电流密度下循环3000次比容量保持在93.4%,具有很好的稳定性.MnO_x/CNFs复合材料电化学性能增强一方面是由于三维超亲水纤维膜结构有利于电解液的快速浸润渗透,从而极大缩短了传输到材料基质的有效路径;另一方面是由于碳和MnO_x的协同效应,包裹在MnO_x粒子周围的碳层避免了MnO_x在充放电过程中的体积膨胀效应,这2种叠加机制促进了电化学性能的提升.     

The application of composites in aerospace

After the introduction of the advanced composite materials, i.e. carbon- and aramidfibre reinforced thermosets, in the late 60's, for a long time the application of these materials used to be considered a panacea for many problems in civil aircraft structures. After many years of trial and error, it is becoming clear that these materials most certainly contribute to better aircraft, but are not a miracle cure. And if there is a key role for composite materials, there is still a long way to go to the all composite (commercial) aircraft. The applications in the aerospace market started with components that used to be designed in glassfibre reinforced thermosets. Although the manufacturing technology was well known, the approach to designing in advanced composites changed in the sense, that the designs had to be optimized for minimum weight (to obtain lower DOC). Also the materials had to be recognized by the designer as being anisotropic (high allowable stresses in the fibre direction). Soon it became evident that also the material- and process technology had to be optimized for the advanced composites. Due to the cost involved in the manufacturing of highly loaded composite components, the design philosophy changed from design for minimum weight to (more or less) design for minimum cost. Also the service experience and resulting remarks from the operators, changed the design approach. The maturity of automated manufacturing will enable further cost reduction and after sufficient service experience with the components that are flying at this moment, the aircraft industry will be ready for the next step: the application of the advanced composite materials in primary, flight-critical aircraft components. The close cooperation between the aerospace industry and the material suppliers will be an essential condition for success in the quest for a “better” aircraft.     

Effect of chemical structure on the liquid crystallinity of banana-shaped molecules

Banana-shaped molecules having two side wings attached to a bent core may exhibit liquid crystallinity. The most studied material is 8-OPIMB that comprises 1,3-dihydroxybenzene as a central core, a Schiff 's base moieties as the wing groups and octyloxy tail groups. To clarify the effect of chemical structure on the liquid crystallinity of such a molecule, we have prepared several banana-shaped molecules, with side wings and central cores different from those of 8-OPIMB and examined their liquid crystallinity, which is sensitive to change in chemical structure. Especially, changing the position of the carbonyl group of the ester function linking the central core to the wing and the position of the nitrogen atom in the Schiff 's base moiety caused a loss of liquid crystallinity. On the other hand, smectic liquid crystallinity was maintained for five new types of banana-shaped molecule with different central cores. Although all these smectic phases have liquid-like association of the molecules within the smectic layers, they showed unconventional smectic textures through the separation of spiral, fractal and germ textures from the isotropic melt. Moreover, a frustrated smectic phase and chiral smectic phases were found. Several possible smectic structures for those phases will be discussed.     

Effect of chemical structure on the liquid crystallinity of banana-shaped molecules

Banana-shaped molecules having two side wings attached to a bent core may exhibit liquid crystallinity. The most studied material is 8-OPIMB that comprises 1,3-dihydroxybenzene as a central core, a Schiff 's base moieties as the wing groups and octyloxy tail groups. To clarify the effect of chemical structure on the liquid crystallinity of such a molecule, we have prepared several banana-shaped molecules, with side wings and central cores different from those of 8-OPIMB and examined their liquid crystallinity, which is sensitive to change in chemical structure. Especially, changing the position of the carbonyl group of the ester function linking the central core to the wing and the position of the nitrogen atom in the Schiff 's base moiety caused a loss of liquid crystallinity. On the other hand, smectic liquid crystallinity was maintained for five new types of banana-shaped molecule with different central cores. Although all these smectic phases have liquid-like association of the molecules within the smectic layers, they showed unconventional smectic textures through the separation of spiral, fractal and germ textures from the isotropic melt. Moreover, a frustrated smectic phase and chiral smectic phases were found. Several possible smectic structures for those phases will be discussed.     

Dynamic Wetting Properties of Mesh Substrates with Tunable Water Adhesion

In nature, wetting phenomena are present nearly everywhere and are a source of inspiration for liquid transportation. A good understanding of the underlying dynamic phenomena that governs wettability is therefore extremely important for researchers involved in bio-inspired surfaces. Herein, we study the adhesive behavior with water of mesh substrates modified with structured copolymers in order to tune the surfaces from parahydrophobic states (high water adhesion) to superhydrophobic states (low water adhesion). Using the ejection test method (ETM), a new technique that consists of the ejection of water droplets deposited onto a substrate with the aid of a catapult system, we experimentally demonstrate that the elasticity of the mesh substrate can be exploited for efficient vertical actuation of droplets.     

Preparation and Characterization of Hydrophobic Nano Silver Film on Butterfly Wings as Bio-template

Hydrophobic nano silver films were fabricated on butterfly wings as bio-template. The micrometric/nano structures and hydrophobicity of the surfaces were investigated with the help of scanning electron microscope（SEM） and video-based contact angle meter. The hydrophobic mechanism of silver film was analyzed with the aid of Cas- sie＇s formula. On the nano silver films of various thicknesses（5, 10, 20, 40, 60, 80, 100 nm）, all the contact an- gles（CAs） of water were bigger than 120°. When the silver film was 5 nm, the CAs of water on it on the wing surfa- ces of Mimathyma nycteis and Speyeria aglaja were 143.2° and 139.2°, respectively. Coated with the sliver film of the same thickness, butterfly wing surface exhibited the CA remarkably bigger than glass slide surface, exhibiting its high hydrophobicity. With the increase of silver film thickness on butterfly wing surface, the hydrophobicity kept de- creasing. The micrometric/nano hierarchical structures on butterfly wing surface result in the transition of metal silver from hydrophilicity to hydrophobicity.     

Wing wettability of Odonata species as a function of quantity of epicuticular waxes

Dragonflies have gained much attention due to their sophisticated wing surface structure, and their associated superhydrophobic, self-cleaning and bactericidal properties. In this work, we compared and contrasted the chemical composition and surface morphology of the wing membranes of four species of dragonfly and damselfly from the Odonata family collected in 1970s (Diplacodes melanopsis and Xanthagrion erythroneurum) and 2011 (Diplacodes bipunctata, and Ischnura heterosticta). Diplacodes species are dragonflies, whilst Xanthagrion and Ischnura are damselflies. Fourier-transform infrared spectroscopy data obtained from the Australian Synchrotron were used to classify the fundamental components of all four of the insect species’ wings. The spectra of all species were dominated by CH stretching, amide I and amide II and OH stretch absorbance indicating the presence of a similar membrane composition of chitin, protein and wax in all four species. Although the samples were collected 40 years apart, there was no evidence of degradation having taken place during this time. Despite the overall similarities in spectral profile, species-specific differences were observed, most notably in the intensity of the νCH₂ peaks, which in part reflected the amount of waxes present on the wings, which appeared to be different between individual species. The surface topography also contained minor differences in the diameter and the spacial distribution of its nanopillars. It is postulated that the differences in surface wettability of the wings could be attributed to these minor differences in surface chemistry and surface topography. For example, X. erythroneurum presented the highest water contact angle (WCA) of 160° whilst the D. melanopsis wings exhibited the lowest WCA (138°), and the wettability of their wings was found to directly correlate with the intensity of hydrocarbon peaks found in their respective IR specta.     

Microencapsulated ammonium polyphosphate with urea–melamine–formaldehyde shell: preparation,characterization, and its flame retardance in polypropylene

Microencapsulated ammonium polyphosphate (MCU‐APP) with urea–melamine–formaldehyde (UMF) resin is prepared by in situ polymerization, and is characterized by FTIR and XPS. The microencapsulation of APP with the UMF resin leads to a decrease in the particle's water solubility. The flame retardant actions of MCU‐APP and APP in PP are studied using limiting oxygen index (LOI) and UL‐94 test, and their thermal stability is evaluated by thermogravimetric analysis. It is found that the LOI value of the PP/MCU‐APP composite is higher than the value of the PP/APP composite. In comparison with the PP/MCU‐APP composites, the LOI values of the PP/MCU‐APP/DPER ternary composites at the same additive loading increase, and UL‐94 ratings of most ternary composites are raised to V‐0. The water‐resistant properties of the PP composites containing APP and MCU‐APP are studied. Moreover, the combustion behavior of the PP composites is investigated by the cone calorimeter. Copyright © 2008 John Wiley & Sons, Ltd.     

Wettability of dragonfly wings: the structure detection and theoretical modeling

Hydrophobic surfaces have gained extensive attention in recent decades for their potential applications. The hydrophobic properties of dragonfly's (Pantala flavescens) wings were measured, and the water contact angles (WCAs) of the distal and basal part of a dragonfly's wing were 134.9° and 125.8°, respectively. Images obtained by optical microscopy and scanning electron microscopy showed the microstructures and nanostructures on the wing surface. Microstructures appeared as cell block patterns, and the size of the blocks decreased from the basal to distal part. However, no significant differences of chemical composition between the two parts were detected by X‐ray photoelectron spectroscopy. To understand the correlation between the structures and WCA, a double roughness structure model was built theoretically with simplified lattice patterns, and the theoretical model was well fitted with empirical wettability of the dragonfly's wing. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and properties of a copolymer of poly(l,4-phenylene sulfide)-poly(2,4-phenylene sulfide acid) and its nano-apatite reinforced composite

A new kind of copolymer of poly(1,4-phenylene sulfide)-poly(2,4-phenylene sulfide acid) (PPS-PPSA) and its nano-apatite (NA) composite have been obtained by polycondensation in l-methly-2-pyrrolidone (NMP). The NA content in the composite can reach 60 wt.%. The structures and properties of copolymer and its NA composite were studied though infrared spectroscopy. X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy. The copolymer has high molecular weight and excellent thermal properties. There is a stable interface formed between NA and PPS-PPSA copolymer in the composite. NA keeps the original morphological structure and crystal behavior in the composite. The composites have good homogeneity and outstanding thermal stability. NA particles are uniformly distributed in the composite. The diameter of apatite in the composite is about 40-60 nm. The PPSA in the copolymer can increase the affinity to apatite and does not decrease the melting point and thermal stability of copolymer.     

Co-microencapsulate of ammonium polyphosphate and pentaerythritol in intumescent flame-retardant coatings

Co-microencapsulated ammonium polyphosphate (APP) and pentaerythritol (PER) [M (A&P)] is prepared using melamine–formaldehyde resin by in situ polymerization method and characterized using energy dispersive spectrometer and Fourier transform infrared spectra. Thermal stability and fire resistance behavior have been analyzed and compared. The co-microencapsulation of APP and PER leads to a great improvement of its thermal stability investigated by thermogravimetric analysis. The temperature of maximum mass loss rate of M (A&P) is 30 °C higher than that of APP/PER mixture. The flame-retardant effect of M (A&P) in coating composite is evaluated by carbonization volume, flame spread rate, and cone calorimeter. Results show that the flame-retardant properties of M (A&P) in coating composite is much better than that of APP/PER mixture coating composite.     

Redox-switchable superhydrophobic silver composite

Unique packaging of Ag(2)O on the surface of polycrystalline AgCl allows fabrication of a new useful, superhydrophobic composite material. This pure inorganic material with surface porosity of submicrometer aperture size fabricates air pockets, which make the composite material superhydrophobic. The new material behaves like lotus leaves, butterfly wings, or water strider's leg in relation to superhydrophobicity. Visible light induces photoreduction of solid Ag(2)O surface layer and generates Ag(0), making the composite surface superhydrophilic. Reoxidation of Ag(0) on the composite surface gives back the hydrophobicity that represents the redox-switchable wetting property of the material.