Band 21, Heft 1

Two new samples of poly(amide-imide) (PAI)/nanocomposites reinforced montmorillonite containing N , N ′-pyrromelitoyl-bis- l -valine moiety in the main chain were synthesized by a solution intercalation technique. PAI 3 as a source of polymer matrix was synthesized by the direct polycondensation reaction of N , N ′-pyrromelitoyl-bis- l -valine 1 with 4,4′-diamino diphenyl ether 2 in the presence of triphenyl phosphite, CaCl 2 , pyridine and N -methyl-2-pyrrolidone. The morphology and structure of the resulting PAI-nanocomposite films 4a and 4b with 5% and 10% silicate particles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The effect of clay dispersion and the interaction between clay and polymeric chains on the properties of nanocomposites films were investigated by using UV-visible spectroscopy, thermogravimetric analysis and differential scanning calorimetry.

Epoxy resin grafted with polyurethane was synthesized and characterized through a series of tests. The grafting reactive process between the pendant secondary hydroxyl groups on the side chains of epoxy resin and the isocyanate groups of pre-polyurethane were investigated by Fourier transform infrared spectroscopy. Thermal behavior of the grafted epoxy resin was investigated by thermogravimetric analysis within 40–500°C. The degradation of grafted epoxy resin involved two stages. Microstructures of the polyurethane section and grafted epoxy resin were observed by field emission scanning electron microscopy. Model fitting method was employed to calculate the thermal degradation model of grafted epoxy resin. In this paper, 15 typical kinetic mechanisms were introduced into the model fitting method, such as Coats-Redfern method and Achar-Brindley-Sharp-Wendworth method, to obtain the kinetic function of thermal degradation for grafted epoxy resin.

The effect of the incorporation of single-walled carbon nanotubes (SWNT) on the morphological, physical, rheological and mechanical properties of thermoplastic elastomer based polypropylene (PP)/ethylene propylene diene (EPDM) (80/20) is reported. The morphological study showed that the size of the dispersed phase decreased by the addition of SWNT, this effect being more appreciable with 0.5 wt.% of SWNT. The results of differential scanning calorimetry showed that the addition of SWNT increased the crystallinity of PP/EPDM/SWNT nanocomposites. This effect was not linearly dependent on SWNT content, particularly at high SWNT concentrations. The rheological results revealed that addition of SWNT increased the storage modulus and complex viscosity at low frequencies. The Izod impact strength and tensile strength improved when 0.5 wt.% of SWNT was used. Furthermore, the tensile modulus increased remarkably by increasing the SWNT content, but the elongation at break of the material decreased.

Thermoplastic poly(phenylene oxide) (PPO)-matrix composites were prepared and characterized in order to evaluate the effect of different ceramic fillers on the thermal and combustion behavior of the matrix. In particular, ceramic particles having three different shapes were exploited as fillers, particles showing a platelet-like, a needle-like or an equiaxial morphology. The composite materials were produced through a melt blending method, which yielded a homogeneous distribution of the ceramic particles in the organic matrix. It was demonstrated that the presence of the inorganic particles influenced the temperature range in which the degradation processes of the polymer occurred. In addition, the three fillers modified the thermal behavior of PPO differently in terms of enthalpy. Finally, the presence of the filler induced a change in combustion behavior of the polymeric matrix; in particular, sepiolite was able to increase the charring ability of the PPO/polystyrene blend with the development of a visible carbonaceous layer.

An aluminum-copper matrix composite reinforced with aluminum diboride particles was studied at high temperature via thermomechanometry experiments. The matrix contained 2 wt% Cu, whereas the amount of boron forming AlB 2 ranged from 0 to 4 wt%, i.e., 0 to 8.31 vol% of diboride particles. In the first segment of the research, we demonstrated that larger amounts of AlB 2 particles raised the composite hardness even at 300°C. To assess the material creep behavior, another set of specimens were tested under 1 N compression at 400°C and 500°C for 12 h. Higher levels of AlB 2 allowed the composites to withstand compression creep deformations at those temperatures. By using existing creep models developed for metal matrix composites we were able to determine that viscous slip deformation was the dominant deformation mechanism for the temperatures and stress levels used in our experiments. Additionally, the computed creep activation energy for these aluminum matrix composites were found comparable to the energies reported for other similar materials, for instance, Al/SiC p composites.

Ultrafine matrix composite powder was prepared from brown corundum slag, grinding balls, anhydrous ethanol, and modifier using a planetary ball mill. The adsorption material was used for dyeing wastewater treatment. A pH instrument, spectrophotometer, and digital water bath oscillator were used to study the amount of modifier, milling speed, milling time, ball-to-powder weight ratio, and slurry concentration to investigate the effects of preparation conditions on the adsorption performance of adsorbent material. The prepared adsorbents and activated carbon were used to adsorb methylene blue in solution under the same conditions to compare adsorbent dosage, adsorption time, temperature, pH of solution, and initial concentration of methylene blue and to study their effects on methylene blue decolorization rate. The experiment results show that dosage of R of 7.5%, ball-to-powder weight ratio of 14:1, rotational speed of 500 rpm, slurry concentration of 20%, and ball milling time of 2.5 h were the optimum parameters. The composite powder (4 g/l) was added to methylene blue wastewater (35 mg/l), pH was adjusted to 6, and adsorption was carried out for 0.5 h at 30°C. The removal rate reached 99.4%.

The high temperature caused by current-carrying wear could affect the thermal reliability of resin-based contact strip greatly. This study adopted liquid-phase impregnation-carbonization (IC) technique to improve the thermal stability and densification of carbon fiber reinforced contact strip (CFRCS). The influence of this method was investigated by scanning electron microscopy, Fourier transform infrared spectrometry, thermal gravimetric analysis and energy-dispersive spectrometry; meanwhile, specimen composition and friction and mechanism properties were also analyzed. The results show that heat treatment is helpful in improving the material’s temperature tolerance. When specimens undergo IC treatment four times, resistivity and wear rate would reduce gradually under impregnating conditions of carbonization temperature (800°C), dipping liquid concentration (60%), and dipping temperature (60°C). IC treatment is effective in reducing material porosity and improving the impact resistance performance compared with only carbonized sample. Densification treatment can also improve the samples’ compressive strength and bending strength. The main wear mechanisms of CFRCS-25 and CFRCS-800 against copper with electrical current are similar; these are arc erosion wear and oxidation wear accompanied by adhesive wear. Adhesive wear and oxidative wear is more severe for CFRCS-25 than CFRCS-800.

The use of waste materials as an additive in soil stabilization has been widespread. This is important in terms of recycling of waste materials and reducing environmental pollution. The objective of this study is to investigate the beneficial reuse of marble dust and fly ash in soil stabilization. Tests were performed on clay soil mixtures amended with marble dust and fly ash. Marble dust was used as an activator due to fly ash being inadequate for self-cementing. Unconfined compressive strength ( q u ), freeze-thaw, swelling, and California bearing ratio (CBR) tests were conducted to investigate the effect of marble dust and fly ash, curing time, and molding water content on geotechnical parameters. Addition of marble dust and fly ash increased unconfined compressive strength, CBR, and freeze-thaw strength, but these additives decreased swelling potential and grain loss after freeze-thaw. Increasing the curing time results in increased strength of mixtures and decreased grain loss. As a result, this study shows that the geotechnical properties of clay soil are improved with the addition of marble dust and fly ash. This is an economical and environmentally friendly solution.

Adhesion between aggregate and bitumen is an important parameter of the performance of bituminous hot mix pavements. Dust on the aggregate surface adversely affects bituminous hot mix pavement performance and leads to some types of deterioration, such as raveling, rutting, stripping, and segregation, decreasing long-term pavement performance. The main objective of this study is to determine the effects of different dust contents of the aggregate surface on the bituminous hot mixture. Two separate aggregate specimens with contents of three different dusts were used to produce bituminous hot mixture specimens. Specific gravity, unit weight, gradation analysis, water absorption, Los Angeles abrasion, aggregate impact, freezing and thawing, Nicholson stripping, and Vialit adhesion tests were performed as aggregate tests, whereas Marshall stability and flow, Marshall mechanical immersion, and indirect tensile tests were performed as bituminous hot mixture tests. The study results show that dust content on the aggregate surface weakens adhesion, leading to the gradual deterioration of the characteristics of the hot bituminous mixtures. Because dust contents on the aggregate surface can vary according to the aggregate type, the progression of the deterioration of bituminous hot mixtures can also vary.

In this paper, the specific absorption rate (SAR) reduction in human head with metamaterial attachment is calculated. The finite-difference time-domain (FDTD) method has been used to evaluate the SAR in an anatomically correct model of the human head. We designed the double-negative metamaterials by placing periodic array arrangement of split ring resonators (SRRs). By properly designing and tuning the structural parameters of SRR S , the effective medium parameters can be made negative at 900 and 1800 MHz band, as presented in this paper. Experimental results show that, with presence of resonators, SAR reduction in the human head is achievable. These results can provide useful insight into the design of safety-compliant mobile communication equipment.

Initial stress (pre-stress) in functionally graded material (FGM) structures is often inevitable because of the limitation of available manufacturing technology. On the basis of the “mechanics of incremental deformations”, the circumferential wave characteristics in FGM cylindrical curved plates under uniform initial stresses in the radial and axial directions are investigated. The Legendre polynomial series method is used to solve the coupled wave equations with variable coefficients. Through numerical examples, the convergence of the polynomial method is discussed. The influences of the initial stresses on the circumferential Lamb-like and the circumferential SH waves are investigated, respectively. Numerical results show that they are quite distinct. Moreover, the influences of the initial stress in the axial direction are very different from those in the radial direction, both on the dispersion curves and on the displacement and stress distributions.

A solution for the transverse thermal conductivity ( K e ) of unidirectional fibre arrays, quadratic and hexagonal, is developed analytically. The solution integrates the thermal conductivity of fibre ( K f ) and fluid ( K m ) based on electricity analogy without thermal contact resistance ( R c ) at the fibre/fluid interface. The expression K e is a function of K f and K m , as well as of the fibre volume fraction ( V f ). In this article, K e values of four composites were predicted and verified by computational fluid dynamics (CFD) simulations. The results showed good agreement when the ratio of K f / K m is close to 1. An increase in the ratio or V f gives poorer agreement owing to the local temperature gradient at the fibre/fluid interface. CFD simulation also showed that K e is decreasing as the R c value increases.

This experimental study deals with the impact response of composite plates manufactured with stitch-bonded non-crimp glass fiber fabrics. Three kinds of fabrics – biaxial, triaxial, and quadraxial – are used as reinforcing material. Polyester resin is used as a matrix material in the composition of composite plates. An instrumented drop weight impact testing machine, Instron-Dynatup 9250 HV, is used for impact testing. Impact tests are performed under various impact energies, ranging from damage initiation to final perforation. An energy profiling method, showing the relation between impact energy and absorbed energy, was used together with load-deflection curves to determine the penetration and perforation thresholds of those composites. The failure processes of damaged specimens for different impact energies were evaluated by comparing load-deflection curves and images of damaged samples taken from the impacted and non-impacted sides. All types of composites have obvious penetration and perforation thresholds. The perforation threshold of triaxial/polyester composite is approximately 27% and 22% higher than that of the quadraxial and biaxial/polyester composites, respectively.

A kind of reliability analysis method for C/SiC woven composite components was proposed, which is based on moment methods. Moment methods combining with perturbation method, the central difference method, as well as the Edgeworth series are applied to calculate the reliability of complex component for its effectivity and accuracy. The results computed by moment methods are sensitive to the distribution of parameters; thus, reliability sensitivity analysis has been performed. The reliability and sensitivity information of the complex components can be accurately and quickly obtained using a practical computer program. Finally, the proposed reliability-sensitivity analysis method is applied to CMCs components design. By comparing with Monte Carlo simulation, the numerical results demonstrate that the proposed approach provides accurate, convergent, and computationally efficient for finite element method-based reliability analysis in engineering practice.

In this study, it was aimed to investigate the effects of fabric lamination angle and fabric ply number on electromagnetic shielding effectiveness (EMSE) of weft knitted fabric-reinforced polypropylene composites. Knitted fabric-reinforced composites are composed of aramid yarn, polypropylene yarn, and copper wire. Polypropylene is the matrix phase and the aramid yarn and copper wires are the reinforcement phase of the composite materials. It was achieved to form 1.5 to 3 mm thickness composites. The composites have nearly 20–50 dB electromagnetic shielding values. To form the knitted fabrics, 7G semiautomatic flat knitting machine was used. The composites were formed by a laboratory-type hot press. EMSE of composites were tested by using ASTM D 4935 coaxial test fixture in 27–3000 MHz frequency band. Lamination angle and ply number parameters were examined related to EMSE of structures. For this study, three different structures were knitted and named as plain knit, 1×1 rib knit, and half cardigan knit. To determine the effect of lamination angle of composites on electromagnetic shielding performance, the composites were produced in two different lamination angles as 0°/90°/0°/90° and 0°/45°/0°/45°. To determine the effect of fabric ply number of composites on electromagnetic shielding performance, the composites were produced in two and four plies. It was observed that the fabric ply number and lamination angle does not affect the EMSE of composite materials very much. It was determined that weft knitted reinforced composite structures have appropriate and high EMSE values for electromagnetic applications. This knitted fabric-reinforced polypropylene composites are flexible and suitable for other industrial applications as civil engineering, aerospace, etc.

A numerical and experimental investigation for the analysis of delamination problem under mode I loading in composite material is presented. Firstly, the simulation of the delamination under mode I loading and failure of composite materials based on the cohesive segments model is investigated by using the meshfree method. With the partition of unity of moving least-squares shape functions, the discontinuities at the cohesive segments are approximated with additional degrees of freedom at the nodes. An iterative solution scheme between the continuous and discontinuous fields is presented to solve mode I delamination growth. Secondly, to verify the meshfree method’s results, an experimental investigation and the finite element method were used for the simulation of delamination. The experimental study used a double-cantilever beam made of carbon/epoxy laminate (AS4/3501-6) which consists of 10 plies in [0] 10 and [0/90/0/90/0] s layup with delamination inserted in the middle of the laminate. The critical fracture force, which can be experimentally measured, was used to calculate the mode I delamination fracture toughness of the carbon/epoxy laminate. Results obtained from the meshfree method showed very good agreement with experimental data for single-mode delamination under mode I loading. The meshfree method could also be used effectively to produce delamination growth in composite laminates and is especially suitable for the simulation of complex delamination patterns that are difficult to model using traditional numerical methods.