Advanced Materials Research Vols. 47-50

Abstract: The compatibility of various electrolyte and electrode combinations has been assessed based on viewpoints of mechanics. The membrane-electrode assembly (MEA) was mainly comprised of traditional ceramic-metal materials as well as solid electrolytes. Variations of key variables such as size and coefficient of thermal expansion were incorporated into ABAQUS sensitivity analyses. Accordingly, general design rules in manufacturing solid oxide fuel cell (SOFC) were proposed, and these rules were beneficial to produce multilayer MEA in the future.

Abstract: Functionally gradient materials (FGMs) composed of 3YSZ and IN713LC were developed in three different configurations. A linear-mode FGM had its compositions with a monotonic change in coefficient of thermal expansion (CTE). Negative- and positive-deviated FGMs had their compositions with lower and higher CTEs, respectively, on the ceramic sides. Fracture behaviors of these three types of FGMs were evaluated with aids of residual stress analyses. FGMs with a positive CTE deviation demonstrated the best performance in the experiment. The brittle ceramic side was under high compressive stress, and high tensile stresses were primarily initiated in the metal-rich gradient layers.

Abstract: As stress waves decay as they pass through the pile foundation system, it is extremely challenging for all nondestructive testing methods to evaluate the pile integrity of a shaft underneath a structure. In this study, time–frequency signal analysis (TFSA) is used for signal processing and adopted to interpret the pile integrity testing signal. An experimental case with pile lengths of 58m with caps, were tested by the low strain sonic echo method. Traditional time domain analyses can not identify the pile tip response signals 58m lengths. After time-history curves are transformed into a time–frequency domain distribution, the results indicate the pile tip can be located more easily and clearly than the traditional time-domain analyses of pile integrity testing allowed for.

Abstract: Machining parameters such as speed (v), feed (f) and depth of cut (d) play an important role in determining the residual stress as well as the surface roughness of a material. The material used for the present study is a nickel based super alloy Udiment 720 which finds applications in the manufacture of gas turbine engine components. Residual stress and surface roughness measured on this material showed different magnitudes for different combinations of milling parameters but did not reveal any definite trend. Analytical relationships developed between the magnitudes of residual stress, surface roughness and milling parameters indicated that combined effects of the milling parameters influence both residual stress and surface roughness.

Abstract: The recent results in constructing the mathematical basis of nonlinear acoustic techniques for NDE of inhomogeneous materials are discussed. These include microstructural materials and materials with weakly or strongly changing properties of specimens (structural elements) under inhomogeneous prestress. The idea is to extract additional information from nonlinear and dispersive effects of wave propagation. Novel concepts are introduced: (i) the analysis of dispersive effects; (ii) the analysis of two counter-propagating nonlinear waves.

Abstract: Polypropylene/polyamide-6 and polypropylene/metallocene polyethylene blends containing 2.5 phr of organophilic modified montmorillonite were prepared in a twin-screw extruder followed by injection molding. In order to compare, blends without layered clay were also made. Styreneethylene- butylene-styrene copolymer and polypropylene grafted with anhydride maleic were used as compatibilizers in the ternary blends and in the PP nanocomposite preparation, respectively. The presence of tactoids, intercalated and exfoliated structures was observed by TEM in some of the samples containing layered clay and modified PP materials. Results showed that the compatibilized blends prepared without clay are tougher than those prepared with the nanocomposite of PP as the matrix phase and no significant changes in tensile moduli were observed between them. However, the binary blend with a nanocomposite of PP as matrix and metallocene polyethylene exhibited better tensile toughness and lower tensile modulus, than those prepared with a nanocomposite of PP and polyamide-6 as dispersed phase. These results are related to the degree of clay dispersion in the PP and to the type of morphology developed in the different blends. Differential scanning calorimetry (DSC) showed that blends with a finer and homogeneously dispersed morphology determined by SEM, the PA component exhibited fractionated crystallization exotherms in the temperature range of 159-185°C. Also, nucleation of the PP component by PA phase and/or the layered clay was observed in the blends with PA as dispersed phase.

Abstract: The results of experimental research of physical and chemical transformations in a ferrous target, caused by intensive deformation mobility of its structural elements for times of shock-wave treatment (∼10–3 sec), at simultaneous development of process of superdeep penetration of lead microparticles are represented.

Abstract: A new configuration of smart structures which could be automatically adjusted according to changes of forcing frequencies is proposed for vibration suppression. The new configuration is a laminated beam-plate or wide beam composed of layers of piezoelectric sensors and actuators and Shape Memory Alloy (SMA) wires embedded in the middle plane of the laminated structure. The structural natural frequencies can be adjusted closely to the forcing frequencies by adjusting electric heating for controlling temperature of SMA. In each layer, the piezoelectric sensors and actuators whose electrode are trimmed to modal shapes in conjunction with proper control algorithm, to achieve expected control effects. The sensors and actuators are connected with each other if they have the same shapes and they are linked together by a controller to form a close loop feedback control. Using active control algorithm to control behavior of the piezoelectric material can suppress the structural vibration. Theoretical simulations are formulated and performed without physical experimentation for evaluating its feasibility. The Hamilton's principle is used to derive the governing equation and boundary conditions for the structure which is composed of PVDF and SMA materials. Modal analysis is used to obtain the result of dynamical response.

Abstract: Mechanical sensitivity of a bossed and clamped layered isotropic circular plate with pretension in large deflection is evaluated. The approach extends Von-Karman’s plate theory for large deflection to a symmetrically layered plate with a center boss. The derived nonlinear governing equations are solved using a finite difference method incorporating a numerical iteration scheme in finding the lateral slope and radial force resultant. The obtained geometrical responses are further manipulated to calculate the associated mechanical sensitivity. For a 3-layered plate with nearly the same layer moduli, the results correlate well with those following available formulation for a single-layer isotropic plate. The developed approach is then implemented for various initial tensions, lateral pressures as well as different boss sizes and ratios between the layer moduli. The obtained numerical results show that, initial tension appears to have the strongest influence upon the radial variation of mechanical sensitivity over the top surface of the bossed layered plate. While both the size of center boss and magnitude of lateral pressure can still have a significant effect, the mechanical sensitivity seems to be insensitive to the change of the ratio between layer moduli for a bossed and symmetrically layered plate.