A two-dimensional,higher-order,elasticity-based micromechanics model

A new, two-dimensional (2D) homogenization theory is proposed. The theory utilizes a higher-order, elasticity-based cell model (ECM) analysis. The material microstructure is modeled as a 2D periodic array of unit cells where each unit cell is discretized into four subregions (or subcells). The analysis utilizes a (truncated) eigenfunction expansion of up to fifth order for the displacement field in each subcell. The governing equations for the theory are developed by satisfying the pointwise governing equations of geometrically linear continuum mechanics exactly up through an order consistent with the order of the subcell displacement field. The formulation is carried out independently of any specified constitutive models for the behavior of the individual phases (in the sense that the general governing equations hold for any constitutive model). The fifth order theory is subsequently specialized to a third order theory. Additionally, the higher order analyzes reduce to a theory equivalent to the original 2D method of cells (MOC) theory when all higher order terms are eliminated. The proposed 2D theory is the companion theory to an equivalent 3D theory [T.O. Williams, A three-dimensional, higher-order, elasticity-based micromechanics model, Int. J. Solids Struc., in press].Comparison of the predicted bulk and local responses with published results indicates that the theory accurately predicts both types of responses. The high degree of agreement between the current theory results and published results is due to the correct incorporation of the coupling effects between the local fields.The proposed theory represents the necessary theoretical foundations for the development of exact homogenization solutions of generalized, two-dimensional microstructures.     

Predicting vibration-induced displacement for a resonant friction slider

A mathematical model is set up to quantify vibration-induced motions of a slider, sandwiched between friction layers with different coefficients of friction, and equipped with an imbedded resonator that oscillates at high frequency and small amplitude. This model is highly nonlinear, involving non-smooth functions with strong harmonic excitation terms. The method of averaging is extended to hold for systems of this class, and used to derive approximate expressions for predicting average velocities of the slider. These expressions are shown to produce results that agree very well with numerical integration of the full equations of motion. The expressions are used to estimate and explain the influence of system parameters.     

Study on a novel manufacturing process of membrane electrode assemblies for solid polymer electrolyte water electrolysis

A novel manufacturing process for catalyst coated membrane (CCM) was utilized to fabricate the membrane electrode assemblies (MEA) for solid polymer electrolyte (SPE) water electrolysis. The properties and performance of the modified CCM were analyzed and evaluated by SEM, electrochemistry impedance spectroscopy (EIS) and I–V curves. The characterizations reveal that the sprayed Nafion layers are very effective for increasing the reaction interface between SPE and the electrode catalyst layer. The test experiments show that the SPE water electrolyzer with new MEA structure can lower about 0.1 V of water electrolysis voltage at atmosphere pressure and 2 A cm⁻².     

Electron localization length in polyaniline

Electrical DC conductivity, magnetic susceptibility, and EPR measurements are used to investigate the electron localization behavior of polyaniline as a function of the dopant type using seven sulfonic acid based doping acids. In spite of differences in the magnitude and the temperature dependences of DC conductivity and magnetic susceptibility data, the experiments reveal a localization length of approximately 30 Å for all the samples. We conclude that this result is essentially due to disorder in the basic morphological structure of a polymer that seems to be determined, among other factors, by the nature of the monomeric units comprising the polymer chains.     

Hysteresis properties for local magnetic sites distribution on grain boundary

Magnetic hysteresis curves were calculated using the Monte Carlo method to study the dependence of magnetic properties on the distribution of local magnetic sites on the grain boundaries of sensitized Alloy 600. The simulated curves illustrate that the total number of the magnetic sites and the standard deviation of the site distribution on grain boundary influence strongly the magnetic remanence and coercivity. The magnetic system can, therefore, be regarded as a magnetic granular structure with a distribution, and the results suggest a possibility of new method to control magnetic hysteresis.     

Structural,electrical, magnetic,elastic and anelastic behaviour of Nd0.6Ca0.4MnO3

With a view to understanding the structural, electrical and magnetic, elastic and anelastic behaviour of charge ordered Nd_0.6Ca_0.4MnO₃, systematic investigations were undertaken. The sample was synthesized by a sol–gel route. The sample was characterized by X-ray diffraction (XRD) using a Rietveld refinement technique and was found to have orthorhombic structure with space group Pnma. A study on the variation of electrical resistivity with temperature has been carried out in the range 100–300 K and it was found to exhibit a field induced transition. The ac susceptibility studies show two transition temperatures, which are attributed to charge ordering and a Néel transition. Internal friction and longitudinal modulus studies were carried out using the composite oscillator technique. An effort has been made to explain the observed anomalous behaviour by a qualitative model.     

Investigation of the thermal decomposition and flammability of PEEK and its carbon and glass-fibre composites

Conventional thermally durable materials such as metals are being replaced with heat resistant engineering polymers and their composites in applications where burn-through resistance and structural integrity after exposure to fire are required. Poly aryl ether ether ketone (PEEK) is one such engineering polymer. Little work has been published with regards to the flammability of PEEK and its filled composites. The current study aims to assess the flammability and fire behaviour of PEEK and its composites using thermogravimetric analysis, pyrolysis combustion flow calorimetry, limiting oxygen index, a vertical flame resistance test, and fire (cone) calorimetry.     

Thermoelectric properties of the LaCoO3-LaCrO3 system using a high-throughput combinatorial approach

A combinatorial film of the LaCo_1-xCr_xO₃ system was fabricated using the LaCoO₃ and LaCrO₃ targets at the NIST Pulsed Laser Deposition (PLD) facility. As the ionic size of Cr³⁺ is greater than that of Co³⁺, the unit cell volume of the series increases with increasing x. Using a custom screening tool, the Seebeck coefficient of LaCo_1-xCr_xO₃ approaches a measured maximum of 286 μV/K, near to the cobalt-rich end of the film library (with x ≈ 0.49). The resistivity value increases continuously with increasing x. The measured power factor, PF, of this series, which is related to the efficiency of energy conversion, also exhibits a maximum at the composition of x ≈ 0.49, which corresponds to the maximum value of the Seebeck coefficient. Our results illustrate the efficiency of applying the high-throughput combinatorial technique to study thermoelectric materials.