Lithium conducting glass ceramic with Nasicon structure

Lithium ion conducting glass and glass ceramic of the composition Li_1.4[Al_0.4Ge_1.6(PO₄)₃], have been synthesized. The monolithic glass pieces on thermal treatment resulted in single-phase glass ceramic with the Nasicon structure. Experiments with different electrodes proved that the lithium electrodes provide accurate values for the ionic conductivity using impedance spectroscopy. σ_ionic of the glass ceramic was found to be 3.8×10⁻⁵ S cm⁻¹ at 40°C with an activation energy (E_a) of 0.52 eV. The corresponding values for the glass are 2.7×10⁻⁹ S cm⁻¹ and 0.95 eV, respectively. The Arrhenius dependence of σ_ionic with temperature in glass and glass ceramic is interpreted with a hopping mechanism from which the microscopic characteristics of the lithium cation motion are deduced.     

Recycled carbon fibre for high performance energy absorption

This paper compares the mechanical properties of virgin and recycled woven carbon fibre prepreg and goes on to assess the potential for recycled carbon fibre reinforced plastic (rCFRP) to be used in high performance energy absorption structures. Three sets of material were examined: fresh containing virgin fibres and resin, aged which was an out of life but otherwise identical roll and recycled which contained recycled fibre and new resin. The compressive strength and modulus of rCFRP were approximately 94% of the values for fresh material. This correlated directly with the results from impact testing where rCFRP conical impact structures were found to have a specific energy absorption of 32.7 kJ/kg versus 34.8 kJ/kg for fresh material. The tensile and flexural strength of rCFRP were 65% of the value for fresh material. Tensile and flexural moduli of rCFRP were within 90% of fresh material and ILSS of rCFRP was 75% that of fresh.     

Synthesis and photoluminescent properties of mesoporous (MgO)x(ZnO)1−x materials

(MgO)_x(ZnO)_1−x materials have been synthesized using mesoporous carbon as template. By increasing the MgO content in the materials greater than 25%, the (MgO)_x(ZnO)_1−x materials began to form the mesoporous structure. Pore size distribution curves indicated that the BJH pore diameter decreased with increasing MgO content. In photoluminescence spectra, all the samples except pure ZnO showed both the band-edge emission and the deep-level emission (green band). It was interesting to note that the UV emission peak energy (E_UV) had a red-shift of about 48 meV at the low MgO content range of 0-25%, while when the MgO content varied from 25 to 75%, the E_UV displayed a blue-shift of about 36 meV to the higher energy direction. The optical band gap (E_g) of the (MgO)_x(ZnO)_1−x calculated from the absorption spectra was far smaller than that in literature, and this may be related to the formation of mesoporous structure.     

Electromagnetic interference shielding behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites

Poly(trimethylene terephthalate) [PTT]/multiwalled carbon nanotube [MWCNT] composites having varying amounts of MWCNTs were fabricated with an aim to investigate the potential of such composites as an effective light weight electromagnetic interference (EMI) shielding material in the frequency range of 12.4-18 GHz (Ku-band). PTT/MWCNT composite with shielding effectiveness (SE) of 36-42 dB was obtained at 10% (w/w) MWCNT loading. Shielding mechanism was studied by resolving the total SE into absorption (SE_A) and reflection loss (SE_R). PTT/MWCNT composite showed absorption dominated shielding; thus it can be used as microwave, radar absorbing and stealth material. The effect of MWCNT loadings on electrical conductivity (σ) and dielectric properties of PTT and the correlation among conductivity, tan δ, absorption loss and reflection loss were also studied.     

Effect of statistical yarn tensile strength on the probabilistic impact response of woven fabrics

The probabilistic impact response of flexible woven fabrics can be described through the V₀–V₁₀₀ or probabilistic velocity response (PVR) curve which describes the probability of fabric penetration as a function of projectile impact velocity. One source of variability that affects the probabilistic nature of fabric impact performance is the statistical distribution of yarn tensile strengths. In this paper the effects of the statistical yarn strength distribution characteristics on the probabilistic fabric impact response are computationally studied using five different strength distributions with differing mean strengths and distribution widths. Corresponding fabric PVR curves are generated for each strength distribution using a probabilistic computational framework that involves randomly mapping yarn strengths onto the individual woven yarns of a fabric finite element model and then running a series of impact simulations for the case of a four-sided clamped fabric impacted at the center by a spherical projectile.     

Thermo-mechanical characterization of Manicaria Saccifera natural fabric reinforced poly-lactic acid composite lamina

The development and thermo-mechanical characterization of a novel green composite lamina, made of PolyLactic Acid (PLA) reinforced with a natural fabric extracted from Manicaria Saccifera palm, are presented. The composite was characterized by thermal-analysis (TGA), tensile, flexural, and izod impact tests, and scanning electronic microscopy (SEM). TGA analysis showed that the degradation process of the composite started earlier than that of neat PLA due to the lower thermal stability of the fabric. The mechanical tests showed that PLA properties were improved. The tensile strength, elastic modulus and impact resistance were improved by 26%, 51% and 56% respectively. Good dispersion and mechanical interlocking of PLA into the fabric were seen by SEM explaining the improvements of the mechanical properties of the composite. In summary, the good tensile properties and the excellent energy absorption capabilities of the MF/PLA composite lamina show great potential of Manicaria fabric as reinforcement in green composites.     

Notch-texture strengthening mechanism in commercially pure titanium thin sheets

Simultaneous effects of notch and texture on strengthening mechanisms of rolled thin sheets of commercially pure titanium were investigated. The presence of notch led to the restriction of deformation systems and different fracture behaviors compared to un-notched specimens. The loss of material’s ability to accommodate plastic deformation at the notch tip with increase in rolling reductions changed the notch strengthening phenomenon to the notch weakening one. At medium levels of deformation, due to the simultaneous development of a triaxial stress state and strong basal texture at the notch tip, a new strengthening mechanism which is called “notch-texture strengthening mechanism” led to a significant enhancement of tear strength. However, the lack of stress triaxiality in un-notched tensile specimens and a strong basal texture component in other notched specimens reduced the impact of strengthening. It was found that the restriction of deformation systems due to the c-axis compression condition at the notch tip was responsible for this strengthening mechanism.     

New quenched-in fluorite-type materials in the Bi2O3-La2O3-PbO system: Synthesis and complex phase behaviour up to 750 °C

New quenched-in fluorite-type materials with composition (BiO_1.5)_0.94−x(LaO_1.5)_0.06(PbO)_x, x = 0.02, 0.03, 0.04 and 0.05, were synthesised by solid state reaction. The new materials undergo a number of phase transformations during heating between room temperature and 750 °C, as indicated by differential thermal analysis. Variable temperature X-ray diffraction performed on the material (BiO_1.5)_0.92(LaO_1.5)_0.06(PbO)_0.02 revealed that the quenched-in fcc fluorite-type material first undergoes a transformation to a β-Bi₂O₃-type tetragonal phase around 400 °C. In the range 450-700 °C, α-Bi₂O₃-type monoclinic, Bi₁₂PbO₁₉-type bcc and β₁/β₂-type rhombohedral phases, and what appeared to be a ?-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 °C.     

Flammability,thermal and physical-mechanical properties of cationic polymer/montmorillonite composite on cotton fabric

The flammability, thermal and mechanical properties on cotton fabric were improved by being finished with the composite containing montmorillonite. To this aim, polymer dimethyl diallyl ammonium chloride-allyl glycidyl ether (P_DMDAAC-AGE) was prepared and its structure characterized by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (¹H NMR). The quaternary ammonium salt copolymer/montmorillonite composite (P_DMDAAC-AGE/MMT) was obtained by polymer intercalation method. The X-ray diffraction (XRD) indicated that the MMT interlayer spacing increased after the polymer intercalation. Composite materials were loaded onto the cotton fabrics by a dip-pad-dry method. The thermo gravimetric analysis (TGA), vertical flame test and limiting oxygen index (LOI) results showed that the thermal and flammability properties of the cotton fabric were improved after it was finished with the composite. Tensile testing revealed an increase on mechanical properties of the finished fabric, but the physical properties hardly changed from the bending length and whiteness results. Scanning electron microscope (SEM) and energy disperse X-ray spectroscope (EDX) results verified the improvement of those properties due to the presence of montmorillonite in the composite.     

Synthesis and electrorheological performance of nanosized composite with polar inorganic compounds

To obtain an economical and applicable electrorheological (ER) material, a novel nanocomposite composed of polar inorganic compounds, NH₄Al(OH)₂CO₃, AlO(OH) and (NH₄)₂SO₄, has been synthesized using low-toxic and economical and facile starting materials by a simple chemical reaction process. The experimental result shows that this material has better ER performance. The static yield stress (τ_y) of the suspension (50 wt%) of the material in silicone oil reached 22.8 kPa at a DC electric field of 4 kV/mm, and the relative yield stress (τ_r) (the ratio of the yield stresses with to without an electric field) is also higher (12.7-33.3 for different concentration suspensions). The composition, grain size, dielectric and surface properties of the material have been studied by the elemental analyses, X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), dielectric spectroscopy and determinations of the surface area and surface energy of the material. The influences of the grain size, dielectric and surface properties on ER performance of the material have been discussed.     

Effects of camber height and boundary condition on energy absorption of arched composite laminates

The scope of this study on arched composite laminates subjected to low-velocity impact was two-fold. One was to investigate the effect of camber height on energy absorption and the other the effect of boundary condition on energy absorption. All specimens were made of the same prepreg tape material and a cross-ply stacking sequence of [0/90]_3s such that a comparison among flat panels and arched specimens with various camber heights can be made. Analysis on the load–deflection relation, the energy profile and the damage process were of primary interest as they provided the insight into the impact behavior of arched composites. Experimental results showed that the maximum deflection and the energy absorption increased significantly as the camber height increased while the peak load decreased slightly. It was also found that the boundary condition played an important role in the energy absorption process. Frame-clamped specimens experienced higher slippage, and hence higher energy absorption, than bolted specimens. This slippage was observed after impact because the specimen actually would pull out of the frame. Video footage also verified this phenomenon.     

Microstructure and mechanical properties of small amounts of In2O3 reinforced Pb(ZrxTi1−x)O3 ceramics

Piezoelectric Pb(Zr_xTi_1−x)O₃ (PZT) ceramics with small amount (0.5-2.0 wt.%) of In₂O₃ are prepared by conventional sintering method. Based on X-ray diffraction analysis, the tetragonality of PZT matrix decreases with In₂O₃ content, indicating that In₂O₃ diffuses into PZT matrix. The microstructure of PZT matrix is significantly refined by doping small amounts of In₂O₃. The grain size reduction and the matrix grain boundary reinforcement are the probable mechanism responsible for the high strength and hardness in the PZT/In₂O₃ materials. The enhancement in Young’s modulus is attributed to In³⁺ substitution. The decreased tetragonality with In₂O₃ addition results in less crack energy absorption by domain switching and, hence, causes the small reduction in fracture toughness.     

Constitutive base analysis of a 7075 aluminum alloy during hot compression testing

In the field of deformation process modeling, the constitutive equations may properly represent the flow behavior of the materials. In fact, these valuable relationships are used as a calculation basis to simulate the materials flow responses. Accordingly, in the present study a hot working constitutive base analysis has been conducted on a 7075 aluminum alloy. This has been performed using the stress–strain data obtained from isothermal hot compression tests at constant strain rates of 0.004, 0.04 and 0.4 s⁻¹ and deformation temperatures of 450, 500, 520, 550 and 580 °C up to a 40% height reduction of the specimen. A set of constitutive equations for 7075 Al alloy have been proposed employing an exponent-type equation. The related material constants (i.e., A, n and α) as well as the activation energy Q for each temperature regime have been determined. The correlation of flow stress to strain rate and temperature can be deduced from the proposed equations. Furthermore, a change in deformation mechanism has been realized in the semi-solid temperature range. This has been related to the onset of lubricated flow mechanism during processing.     

Influence of anionic vacancies on the ionic conductivity of silicated rare earth apatites

Oxyapatites are very promising materials in terms of ionic conductivity. They can be considered as a potential electrolyte for Solid Oxide Fuel Cells (SOFC). Doped silicated rare earth apatites with formula La_9.33−xCa_x(SiO₄)₆O_2−x/2 (0 ≤ x ≤ 1) have been prepared by solid state reaction at high temperature in order to determine the influence of anionic vacancies on the electrical properties of the material. The incorporation of calcium in the structure has been checked by characterizations of the powders (X-ray diffraction, helium pycnometry). The cell parameters of the hexagonal apatite were refined. Samples were sintered at 1550 °C. Electrical properties of each composition have been studied between 280 and 620 °C by the complex impedance method. The evolution of the bulk conductivity and of the activation energy with the substituting ratio gives information on the conductivity mechanism in these materials. An improvement of ionic conductivity about one order of magnitude has been observed for low calcium substitution ratios.     

The effects of interfacial adhesion strength on the characteristics of an aluminum/CFRP hybrid beam under transverse quasi-static loading

The effects of interfacial adhesion strength on the damage behavior and energy absorption characteristics of an aluminum (Al)/carbon fiber reinforced plastic (CFRP) short square hollow section (SHS) beam under three point bending loading was investigated. An Al SHS beam was wrapped by CFRP with a [0°/+45°/90°/−45°]_n (n = 1 or 2) stacking sequence, and four gradations of interfacial adhesion strength were caused by physical or chemical changes of the Al adherend with different mechanical abrasion and optimal Argon plasma treatment. A different level of appropriate interfacial adhesion strength existed for each hybrid specimen depending on the CFRP laminate thickness to obtain the highest energy absorption capability, and this was verified by detailed observation of the failure mechanism of the hybrid specimen. The specific energy absorbed (SEA) was improved by up to 57.2% in the Al/CFRP [0°/+45°/90°/−45°]₂ SHS beam compared to the Al SHS beam without compromising the crush force efficiency (CFE).     

The influence of a thermoplastic toughening interlayer and hydrothermal conditioning on the Mode-II interlaminar fracture toughness of Carbon/Benzoxazine composites

Carbon fibre/Benzoxazine laminates with and without non-woven polyamide (PA) fibre veils at the interlaminar regions were manufactured using vacuum assisted resin transfer moulding (VARTM). The effect of the interlaminar thermoplastic veils on the Mode-II critical strain energy release rate (G_IIC), under both wet and dry conditions, was determined using two commercially available Benzoxazine resins: a toughened system and an untoughened system. In all samples the toughened system outperformed the untoughened system. The overall resistance to Mode-II crack growth was significantly improved by the inclusion of the interlaminar veils due to an increase in the thickness of the matrix-rich interlaminar region, plastic deformation of the PA fibres and a crack-pinning mechanism. Moisture caused an increase in matrix ductility, which improved the resistance to crack initiation; however, this was counteracted by a reduction in fibre/matrix interfacial strength causing a reduction in resistance to crack growth.     

About the influence of temperature and matrix ductility on the behavior of carbon woven-ply PPS or epoxy laminates: Notched and unnotched laminates

Could thermoplastic-based composites be used to replace thermosetting-based composites in high-temperature secondary aircraft structures? The purpose of this work is to establish the ability of a material system to be used in aircraft engine nacelles when subjected to static loadings, with a key upper temperature of 120 °C. In order to provide answers to this question, the thermo-mechanical behaviors of carbon fiber fabric reinforced PPS or epoxy laminates have been compared specifically within the temperature change with 120 °C at the upper bound. The temperature-dependent ductile behavior of laminates is more or less exacerbated, depending on polymers glass transition temperature, and laminates stacking sequence. For both materials, the degree of retention of tensile mechanical properties is quite high in notched and unnotched quasi-isotropic laminates. A Digital Image Correlation technique has been used in order to understand the influence of temperature and matrix ductility on the mechanisms of overstresses accommodation near the hole. In fabric reinforced laminates, the high-temperature results suggest a competition between the mechanisms of damage, and the mechanism of plasticization, enhanced in angle-ply lay-ups. Thus, the highly ductile behavior of TP-based laminates, at temperatures higher than their T_g, is very effective to accommodate the overstresses near the hole.     

Determination of the damage threshold in woven-ply thermoplastic laminates at T > Tg: Acoustic emission and microscopic damage analysis

An original in situ measurement of acoustic emission (AE) was applied to monitor damage progress in discrete steps during gradual load/unload tensile tests on [±45°]₇ C/PPS laminates at temperatures T > Tg, when matrix ductility is enhanced. In order to understand the specific damage behavior of such materials under severe environmental conditions, AE analysis was accompanied by microscopic observations to detect the damage initiation threshold as well as the damage mechanisms within the composite material. Once the AE source mechanisms have been separated into classes thanks to the pattern recognition software Noesis, they have been identified to match physical phenomena. Earliest cracks events occur at the crimps where the rotation of warp/weft fibres takes place, followed by the intra-bundles splitting on free surface. It is observed that the onset of intralaminar cracking and debonding is affected by the presence of matrix-rich regions between the plies, because of an extensive plasticization of the PPS matrix. The study of the specific acoustic activity of neat PPS resin specimens confirms that the local plastic deformation in matrix-rich areas contributes to delay the initiation of damage, and subsequent AE signals. Finally, AE proved to be a relevant technique to investigate damage mechanisms and to determine accurately the damage threshold in TP-based composites to be used in aeronautical applications at T > Tg.     

Microhardness and high-velocity impact resistance of HfB2/SiC and ZrB2/SiC composites

The results of Vickers microhardness and high-velocity impact tests on monolithic ZrB₂/SiC and HfB₂/SiC ultra-high temperature ceramic (UHTC) composites are presented. The UHTC materials exhibit fracture behavior typical of ceramics under indentation and impact loading. The materials are relatively hard with microhardness values of about 15 to 20 GPa. Cracks were observed to extend from the corners of indentations. Impacts of stainless steel and tungsten carbide spheres, with diameters in the 500 to 800 micron range and velocities of 200 to 300 m/s, produced minimal plastic deformation but significant radial and ring cracking at the impact sites. Impacts of micron-scale iron particles traveling at 1 to 3 km/s produced essentially no surface damage.     

Energy absorption capability of carbon nanotubes dispersed in resins under compressive high strain rate loading

The focus of the present study is on energy absorption capability (E_A) of carbon nanotubes (CNTs) dispersed in thermoset epoxy resin under compressive high strain rate loading. Toward this objective, high strain rate compressive behavior of multi-walled carbon nanotube (MWCNT) dispersed epoxy is investigated using a split Hopkinson pressure bar. The amount of MWCNT dispersion is varied up to 3% by weight. Calculation methodology for the evaluation of E_A of individual CNTs and CNTs dispersed in resins/composites is presented. Quantitative data on E_A of individual CNTs and CNTs dispersed in resins under quasi-static and high strain rate loading is given.