Optical properties of α, β and ω structure of Titanium: Ab initio approach

In this work, a thorough study of the band structure and optical properties of α, β and ω phases of Titanium are presented using the full potential augmented plane wave plus local orbital method (FLAPW + LO) and using the generalized gradient approximation (GGA). The Wien2k package was also used. For optimum optical properties, the optimized lattice constants were considered. The dielectric function, energy loss, optical conductivity and reflectivity of all α, β and ω phases were calculated and compared. Calculations were in agreement with the experimental measurements. Imaginary dielectric functions of ε₂(ω) were peaked at around 0.15 eV while that was around 0.17 eV for the experimental measurements. Reflectivity was consistent with experimental values. Moreover, the effect of phases on the optical properties was investigated. Throughout the phases, ω had the most static dielectric constant ε₁(ω) at around 144.78 and the highest R₀ of 0.8. In general, although β had the highest reflectivity in the photon energy of 3.53 eV, it had the lowest value of all the frequencies.     

Influence of adsorbed moisture on the properties of cyanate ester/BaTiO3 composites

The effect of moisture adsorbed on BaTiO₃ on the properties of cyanate ester (CE)/BaTiO₃ dielectric composites is examined using undried and dried BaTiO₃ particles. The influence of moisture on the dielectric constant, thermal stability, dynamic mechanical properties, flexural behavior and micro morphology of the composites is investigated. Dielectric constant (ε) and dielectric loss (tan δ) of composites with the dried BaTiO₃ are both higher than composites manufactured with undried filler at the same frequency. The dielectric properties of the dried system are stable over a broader temperature range than the undried composites. Adsorbed moisture causes the initial decomposition temperature and the maximum degradation temperature of the composite to decrease by 27 °C and 15 °C, respectively. By removing the moisture from BaTiO₃, the CE/BaTiO₃ composite exhibits a lower modulus (E′), higher strength, higher flexural elongation and a dramatically increased glass transition temperature (T_g).     

Fabrication and characterization of three-dimensional PMR polyimide composites reinforced with woven basalt fabric

A PMR polyimide composite reinforced with three-dimensional (3D) woven basalt fabric is fabricated for medium high temperature applications. The PMR polyimide matrix resin is derived from 4,4′-methylenediamine (MDA), diethyl ester of 3,3′,4,4′-oxydiphthalic (ODPE) and monoethyl ester of Cis-5-norbornene-endo-2,3-dicarboxylic acid (NE). The rheological properties of the PMR polyimide matrix resin are investigated. Based on the curing reaction of the PMR type polyimide and the rheological properties, an optimum two-step fabrication method is proposed. The three dimensional fabric preforms are impregnated with the polyimide resin in a vacuum oven at 70 °C for 1 h followed by removing the solvent and pre-imidization. The composites are then consolidated by an optimized molding procedure. Scanning electron microscopy analysis shows that needle shaped voids are generated in yarns and the void volume fraction is 4.27%. The decomposition temperature and the temperature at 5% weight loss of the composite post-cured at 320 °C for 24 h are 440 °C and 577 °C, respectively. The dielectric constant and the dielectric loss of the composite are measured by circular cavity method at 7–12 GHz. The tensile strength and the modulus in the warp direction of the composite are 436 MPa and 22.7 GPa. The composite shows a layer-by-layer fracture mode in three-point bending test. The flexure strength and modulus in the warp direction of the composite are 673 MPa and 27.1 GPa, respectively.     

Electromagnetic interference shielding of composites consisting of a polyester matrix and carbon nanotube-coated fiber reinforcement

We investigated the electromagnetic interference shielding effectiveness (EMI SE) of composites consisting of an unsaturated polyester matrix containing woven glass or carbon fibers that had been coated with multiwalled carbon nanotubes (MWCNTs). Composite panels consisting of fiber fabrics with various combinations of fabric type and stacking sequence were fabricated. Their EMI SE was measured in the frequency range of 30 MHz–1.5 GHz. The underlying physics governing the EMI shielding mechanisms of the materials, namely, absorption, reflection, and multiple reflections, was investigated and used in analytical models to predict the EMI SE. Simulation and experimental results showed that the contributions of reflection and absorption to EMI shielding is enhanced by sufficient impedance mismatching, while multiple reflections have a negative effect. For a given amount of MWCNTs in the glass-fiber–reinforced composite, coating the outermost, instead of intermediate, glass fiber plies with MWCNTs was found to maximize the conductivity and SE.     

Influence of fiber content on the mechanical and dynamic mechanical properties of glass/ramie polymer composites

The combination of glass and ramie fibers with a polyester matrix can produce a hybrid material that is competitive to all glass composites (e.g. those used in the automobile industry). In this work, glass and ramie fibers cut to 45 mm in length were used to produce hybrid polymer composites by resin transfer molding (RTM), aiming to evaluate their physical, mechanical and dynamic mechanical properties as a function of the relative glass–ramie volume fractions and the overall fiber content (10, 21 and 31 vol.%). Higher fiber content and higher ramie fiber fraction in the hybrid composites yielded lower weight composites, but higher water absorption in the composite. The mechanical properties (impact and interlaminar shear strength) of the composites were improved by using higher fiber content, and the composite with 31 vol.% of reinforcement yielded the lowest value for the reinforcement effectiveness coefficient C, as expected. Although the mechanical properties were improved for higher fiber content, the glass transition temperature did not vary significantly. Additionally, as found by analyzing the adhesion factor A, improved adhesion tended to occur for the composites with lower fiber content (10%) and higher ramie fiber fraction (0:100) and the results for the adhesion factor A did not correspond to those found by the analysis of the tan delta peak height.     

Dielectric,mechanical and thermal properties of polymer/BaTiO3 composites for embedded capacitor

Barium titanate (BaTiO₃) filled polymethylmethacrylate (PMMA) composites were prepared using the simple solution method followed by hot pressing. The content of BaTiO₃ was varied from 0 to 65 vol.%. Scanning electron microscopy showed good dispersion and adhesion of BaTiO₃ with the PMMA matrix. The dielectric constant of the composites increased significantly. There was weak dispersion in the dielectric constant of the composites (up to 45 vol.%) with frequency between 100 Hz and 15 MHz. The dissipation factor of the composites increased from 0.021 for pure PMMA to 0.029 for 45 vol.% composites. However, 65 vol.% composite showed dispersion in dielectric constant with increasing frequency and higher dissipation factor. The Lichtenecker equation agreed well with the experimental data. The microhardness and the glass transition temperature of the composites increased approximately 4.7-fold and 42 °C, respectively, compared to pure PMMA. The CTE of the 65 vol.% composite is close to that of copper.     

Effect of coupling agents on the dielectric properties of CaCu3Ti4O12/PVDF composites

Phase-pure calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) ceramic particles were synthesized via a sol–gel route. The CCTO was treated by bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69) to give CCTO@Si69. The dielectric composites based on CCTO (or CCTO@Si69) and polyvinylidene fluoride (PVDF) were molded with desirable dielectric properties by mechanical mixing process and hot-pressing. The structures of CCTO and CCTO@Si69 were investigated by scanning electron microscopy (SEM) energy spectrum, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The stretching vibration of SO at 1096 cm⁻¹ in FTIR is an indication that chemical bond was formed between Si69 and CCTO. The influence of Si69 on the preparation and the dielectric properties of CCTO/PVDF dielectric composites were discussed. When the content of Si69 was 0.1 mL (relative to 1 g of CCTO), the dielectric constant (ε) (at a frequency of 1 kHz) of CCTO@Si69/PVDF composites reached the maximum value of 84, this value is 5.25 times that of an equal amount of CCTO of CCTO/PVDF composites (ε ≈ 16). The CCTO/PVDF and CCTO@Si69/PVDF composites had very stable dielectric properties over a wide range of temperatures (20–160 °C). These composites can be applied as high-energy–density capacitors in electronic and electrical engineering fields.     

Microstructure of carbon nanotubes/PET conductive composites fibers and their properties

Poly(ethylene terephthalate) (PET) resin has been compounded with carbon nanotubes (CNTs) using a twin-screw extruder. The composites of 4 wt% CNTs in PET had a volume electrical resistance of 10³ Ω cm, which was 12 orders lower than pure PET. The volume electrical conductivity of CNTs/PET composites with different CNTs containing followed a percolation scaling law of the form σ = κ(ρ − ρ_c)^t well. Scanning electron microscopy (SEM) micrograph showed that CNTs had been well dispersed in PET matrix. Optical microscopy micrograph showed that discontinuity of conductive phase existed in some segments of composite fiber. Rheological behavior of CNTs/PET composites showed that the viscosity of CNTs/PET composites containing high nanotube loadings exhibited a large decrease with increasing shear frequency. Crystallization behavior of CNTs/PET composites was studied by differential scanning calorimetry (DSC) and the nucleating effect of CNTs in the cooling crystallization process of PET was confirmed. Composite fiber was prepared using the conductive CNTs/PET composites and pure PET resin by composite spinning process. Furthermore, cloth was woven by the composite fiber and common terylene with the ratio 1:3. The cloth had excellent anti-static electricity property and its charge surface density was only 0.25 μC/m².     

Exploring mechanical property balance in tufted carbon fabric/epoxy composites

The paper details the manufacturing processes involved in the preparation of through-the-thickness reinforced composites via the ‘dry preform–tufting–liquid resin injection’ route. Samples for mechanical testing were prepared by tufting a 5 harness satin weave carbon fabric in a 3 mm × 3 mm square pitch configuration with a commercial glass or carbon tufting thread, infusing the reinforced preforms with liquid epoxy resin and curing them under moderate pressure. The glass thread reinforcement increases the compression-after-impact strength of a 3.3 mm thick carbon fabric laminate by 25%. The accompanying drop-downs in static tensile modulus and strength of the same tufted laminate are below 10%. The presence of tufts is also shown to result in a significant increase in the delamination crack growth resistance of tufted double-cantilever beam specimens and has been quantified for the case of a 6 mm thick tufted carbon non-crimped fabric (NCF)/epoxy composite.     

Effect of fiber morphology on rheological properties of plant fiber reinforced poly(butylene succinate) composites

Sisal fibers (SFs), steam exploded sisal fibers (SESFs) and steam exploded bagasse fibers (SEBFs) which have different fiber morphologies, were mixed with poly(butylene succinate) (PBS) using a torque rheometer. The rheological properties of these plant fiber-reinforced PBS composites were evaluated. Results show that the fiber morphology has a large effect on rheological behavior. At the same fiber content (e.g., 10 wt% and 30 wt%), the non-Newtonian index n of composites reinforced by flexible fibers with a higher aspect ratio and larger contact area with the matrix is smaller. In general, n decreases with increasing fiber content but when the fiber content is too high (e.g., 50 wt%), the aggregation of fibers is too extensive so that the actual contact area between fibers and matrix becomes much lower, n increase instead. At the same fiber content (e.g., 10 wt% and 30 wt%), the consistency indices of fibrous filler-reinforced composites are larger than those of powder-filled composites; the larger the actual contact area between the matrix and the fibers, the greater the consistency index of the composite.     

Electromagnetic shielding effectiveness of copper/glass fiber knitted fabric reinforced polypropylene composites

The main objectives of this research work are to develop conductive knitted fabric composite materials and to determine their electromagnetic shielding effectiveness (EMSE). Polypropylene is the matrix phase and glass fibers are the reinforcement phase of the composite material. Copper wires are incorporated as conductive fillers to provide the electromagnetic shielding properties of the composite material. The amount of copper in the composite material is varied by changing the yarn composition, fabric knit structure and stitch density. The EMSE of various knitted fabric composites is measured in the frequency range of 300 kHz to 3 GHz. The variations of EMSE of knitted fabric composites with fabric structure, stitch density and yarn compositions are described. Suitability of conductive knitted fabric composites for electromagnetic shielding applications is also discussed.     

Interlaminar shear behavior of unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid and non-hybrid composite laminates

The interlaminar shear behavior of unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid composites was studied with short beam shear bending test. Random glass fiber (R)/epoxy means chopped fiber composite having short discontinuous fiber randomly dispersed in epoxy matrix. The effect of stacking sequence and unidirectional glass fiber relative volume fraction (V_fU/V_fT) on the interlaminar shear strength (ILSS) of the manufactured composites has been investigated experimentally and theoretically. The laminates were fabricated by hand lay-up technique with 5 plies. Two non-hybrid composite laminates [R]₅ and [U]₅ were fabricated using the same fabrication technique for the comparison purpose. The average thickness of the manufactured laminates is 5.5 ± 0.2 mm and the total fiber volume fraction (V_fT) is 37%. Failure modes of all specimens were investigated. Experimental results indicated that the ILSS of [U]₅ is higher than those of hybrid and [R]₅ composite. Hybrid composites have higher ILSS than that of random composites. The stacking sequence and (V_fU/V_fT) ratio have a detectable effect on ILSS of the investigated composites.     

Preparation and properties of continuous glass fiber reinforced anionic polyamide-6 thermoplastic composites

Continuous glass fiber (GF) reinforced anionic polyamide-6 (APA6) composites were prepared via in situ ring-opening polymerization of caprolactam monomers. The effects of catalyst content, polymerization temperature and time on the viscosity average molar mass (M_v) and degree of crystallinity (X_c) were investigated in detail. The final mechanical properties of GF/APA6 composites were also studied. The results indicated that both high molecular weight and the high degree of crystallinity of resin matrix lead to the high mechanical properties of composites. Furthermore, the mechanical test results showed that the composites of plain woven fabric had tensile strength of 434 MPa and flexural strength of 407 MPa. The morphologies of tensile fracture surfaces of the composites specimens were observed through Scanning Electron Microscope (SEM). The SEM analysis showed that many disorganized nano-fiber crystals appear in the tensile fracture surfaces, which improve the mechanical properties of the matrix resin. The mechanical properties of the composites with different post-heat treatments were further investigated. The mechanical properties of the composites are significantly reduced after quenching treatment, but hardly improved after annealing.     

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%V_f). The short beam strength increased up to %V_f of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component.     

Electrical properties of nanostructures (CoFeZr)x + (Al2O3)1−x with use of alternating current

CoFeZr–Al₂O₃ nanocomposite films of 3–5 μm thickness, containing metallic alloy nanoparticles embedded into the dielectric alumina matrix, have been deposited on a glass ceramic substrate using magnetron sputtering of composite target in Ar gas ambient. Measurements of AC conductance and lagging have been performed within the frequency range of 50 Hz–1 MHz at the temperatures from 79 K to 373 K in the initial (as-deposited) samples as well as directly after their isochronous (15 min) annealings within the temperature range from 398 K to 648 K with 25 K step.The observed variations of real part AC electrical conductivity with temperature and frequency σ_real(T, f) in the as-deposited films display transition from dielectric to metallic behaviour when crossing the percolation threshold x_C in the studied nanocomposites. After annealing of the samples below the x_C the σ_real(T, f) progress follows the hopping law of electron conductivity with sigmoidal frequency dependence. The samples being far beyond the percolation threshold revealed transition from metallic to activational σ_real(T) law after high-temperature annealing attributed to the internal oxidation of metallic nanoparticle by excess of oxygen presented in the as-deposited samples.     

New electromagnetic wave shielding effectiveness at microwave frequency of polyvinyl chloride reinforced graphite/copper nanoparticles

A novel functional nanoconducting composite from polyvinyl chloride reinforced graphite–copper nanoparticles (PVC/GCu) was fabricated in order to produce a material suitable for electromagnetic interference (EMI) shielding applications. The microstructure of the nanocomposites was investigated by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The thermal stability of the nanocomposites could improved with the incorporation of GCu nanoparticles. The electrical conductivity increases with increasing GCu content within composites. The percolation threshold of composites is low of about 2 wt.%. Hall-effect studies indicate that increase in GCu content in the composites causes increase in carrier concentration, mobility of the carriers and the composites behave as n-type semiconductor. The nanocomposites showed a high dielectric constant and a high dissipation factor in the frequency range of 1–20 GHz which makes it useful in charge storing and decoupling capacitors applications. The EMI shielding effectiveness (SE) of the PVC/GCu nanocomposites was tested over a frequency range of 1–20 GHz, and 22–70 dB shielding efficiency was obtained for the composites, suggesting that they may be used as an effective lightweight EMI shielding material in aerospace and radar evasion applications.     

On the strengthening effect of increasing cycling frequency on fatigue behavior of some polymers and their composites: Experiments and modeling

Effect of cycling frequency on fatigue behavior of neat, talc filled, and short glass fiber reinforced injection molded polymer composites was investigated by conducting load-controlled fatigue tests at several stress ratios (R = −1, 0.1, and 0.3) and at several temperatures (T = 23, 85 and 120 °C). A beneficial or strengthening effect of increasing frequency was observed for some of the studied materials, before self-heating became dominant at higher frequencies. A reduction in loss tangent (viscoelastic damping factor), width of hysteresis loop, and displacement amplitude, measured in load-controlled fatigue tests, was observed by increasing frequency for frequency sensitive materials. Reduction in loss tangent was also observed for frequency sensitive materials in DMA tests. It was concluded that the fatigue behavior is also time-dependent for frequency sensitive materials. A Larson–Miller type parameter was used to correlate experimental fatigue data and relate stress amplitude, frequency, cycles to failure, and temperature together. An analytical fatigue life estimation model was also used to consider the strengthening effect of frequency in addition to mean stress, fiber orientation, and temperature effects on fatigue life.     

Infiltrated Cu8Al–Ti alumina composites

The effect of titanium additions on the interface and mechanical properties of infiltrated Cu8 wt%Al–Al₂O₃ composites containing 57 ± 2 vol% ceramic are investigated, exploring two different Al₂O₃ particle types and four different Ti concentrations (0, 0.2, 1, 2 wt%Ti). Addition of 0.2 wt%Ti leads to the development of a thin (5–10 nm) layer enriched in Ti at the interface between Cu alloy and Al₂O₃ particles; this Ti concentration produces the best mechanical properties. With higher Ti-contents Ti₃(Cu, Al)₃O appears; this decreases both the interface and composite strength. Composites reinforced with vapor-grown polygonal alumina particles show superior mechanical properties compared to those reinforced by angular comminuted alumina particles, as has been previously documented for aluminum-based matrices. Micromechanical analysis shows that damage accumulation is more extensive, as is matrix hardening by dislocation emission during composite cooldown, in the present Cu8 wt%Al matrix composites compared with similarly reinforced and processed Al-matrix composites.     

Effect of fiber loading on mechanical and morphological properties of cocoa pod husk fibers reinforced thermoplastic polyurethane composites

In this study, cocoa (Theobroma cacao) pod husk (CPH) fiber reinforced thermoplastic polyurethane (TPU) was prepared by melt compounding method using Haake Polydrive R600 internal mixer. The composites were prepared with different fiber loading: 20%, 30% and 40% (by weight), with the optimum processing parameters: 190 °C, 11 min, and 40 rpm for temperature, time and speed, respectively. Five samples were cut from the composite sheet. Mean value was taken for each composite according to ASTM standards. Effect of fiber loading on mechanical (i.e. tensile, flexural properties and impact strength) and morphological properties was studied. TPU/CPH composites showed increase in tensile strength and modulus with increase in fiber loading, while tensile strain was decreasing with increase in fiber loading. The composite also showed increase in flexural strength and modulus with increase in fiber content. Impact strength was deteriorated with increase in fiber loading. Morphology observations using Scanning Electron Microscope (SEM) showed fiber/matrix good adhesion.