Viscous flow in variable cross-section microchannels of arbitrary shapes

This paper outlines a novel approximate model for determining the pressure drop of laminar, single-phase flow in slowly-varying microchannels of arbitrary cross-section based on the solution of a channel of elliptical cross-section. A new nondimensional parameter is introduced as a criterion to identify the significance of frictional and inertial effects. This criterion is a function of the Reynolds number and geometrical parameters of the cross-section; i.e., perimeter, area, cross-sectional polar moment of inertia, and channel length. It is shown that for the general case of arbitrary cross-section, the cross-sectional perimeter is a more suitable length scale. An experimental investigation is conducted to verify the present model; 5 sets of rectangular microchannels with converging–diverging linear wall profiles are fabricated and tested. The collected pressure drop data are shown to be in good agreement with the proposed model. Furthermore, the presented model is compared with the numerical and experimental data available in the literature for a hyperbolic contraction with rectangular cross-section.     

Fibre embedding in aluminium alloy 3003 using ultrasonic consolidation process��thermo-mechanical analyses

This work presents a computational framework based on finite element methods to simulate the fibre-embedding process using ultrasonic consolidation process. The computational approach comprises of a material model which takes into account thermal and acoustic softening effects and a friction model which indicates the realistic friction behaviour at the interfaces. The derived material model and developed friction model have been incorporated in finite element model. Using the implemented material and friction model, thermo-mechanical analyses of embedding of fibre in aluminium alloy 3003 has been performed. Effect of different process parameters, such as velocity of sonotrode, displacement amplitude of ultrasonic vibration and applied loads, is studied and compared with the experimental results. The presented work has specially focused on the quality of the developed weld which could be evaluated by the friction work and the coverage of the fibre which is estimated by the plastic flow around the fibre. The computed friction work obtained from the thermomechanial analyses performed in this study show a similar trend as that of the experimentally found fracture energies.     

Effect of Process Parameters on Microstructure and Micro-hardness of AZ91/Al2O3 Surface Composite Produced by FSP

In this article, the effects of three different sizes of Al₂O₃ particles in the friction stir processing on grain size, cluster size, microstructure, and micro-hardness of as-cast magnesium alloy AZ91 were investigated. Moreover, the effects of two types of tool geometries and number of passes on the mentioned parameters were considered. Effect of mentioned parameters on microstructure, grain refinement, and micro-hardness profile in the friction stirred zone of the specimens was compared by as-cast received form and also friction stir processed (FSPed) specimens without particles. Microstructural characterization of the materials revealed reasonably uniform distribution of Al₂O₃ reinforcement and significant grain refinement. Hardness studies revealed that the incorporation of nano- and micro-size Al₂O₃ particulates in magnesium matrix led to a simultaneous increase in hardness.     

Nanometer-sized cerium oxide particles for solid phase extraction of trace amounts of mercury in real samples prior to cold vapor atomic adsorption spectrometry

Ceria (CeO₂) nanoparticles were synthesized using the microwave-assisted heating technique and employed as a sorbent for preconcentration of trace amounts of Hg(II) ions from aqueous solutions for the first time. The analysis of mercury was performed by cold vapor atomic absorption spectrometry (CV-AAS). The characteristics of nanoparticles were assessed using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Experimental parameters influencing the extraction procedure recovery were thoroughly investigated. Under the optimized experimental conditions, the calibration curve was linear in the range of 0.035–0.8 µg/L of mercury. The method was validated by analysis of a certified reference material.     

Examination of an aluminum alloy behavior under different routes of twist extrusion processing

Experiments were conducted to evaluate the effects of loading path during twist extrusion processing. The samples of aluminum 8112 were processed by different routes of twist extrusion. Two consecutive clockwise dies (route I) and alternative clockwise-counterclockwise dies (route II) were used. The grain sizes created by route II were significantly finer than those created by route I. Furthermore, the mechanical properties, including the strength and hardness, not only enhanced but also distributed more homogeneously across the transverse cross-section of the samples.     

Evaluation of rutting resistance of asphalt binders and asphalt mixtures modified with polyphosphoric acid

In this research, a polyphosphoric acid (PPA) additive was used to modify a performance graded binder (PG 58-22). Experimental program included use of three PPA contents (0.5%, 1%, and 1.5%) by weight of bitumen and use of antistripping limestone aggregates. High-temperature rheological properties of asphalt binders were evaluated through the frequency sweep test. Complex modulus test was also used to evaluate rutting characteristics of asphalt mixtures. Results showed that PPA significantly improved rutting resistance of both unmodified asphalt binder and unmodified asphalt mixture, especially for the asphalt binder.     

Ion beam assisted deposition of TiN-Ni nanocomposite coatings

Hard and tough nanocomposite coatings consisting of hard TiN nanograins embedded in a soft metallic intergranular phase of Ni have been produced using ion beam assisted deposition. The chemical composition has been obtained by Rutherford Backscattering and the microstructural properties: phases, grain size, and texture of the coatings have been investigated by X-Ray Diffraction. In the composition range 0-22.5 at.% Ni, δ-TiN is the only crystalline phase and Ni appears as an X Ray amorphous phase. The hardness increases up to a maximum of 41 GPa at ~ 7 at.% Ni which corresponds to a TiN crystallite size of ~ 8 nm and a Ni intergranular phase thickness of roughly 1 monolayer. It is shown that the hardness enhancement in TiN-Ni nanocomposite coatings is not correlated with residual stresses, but rather with the intrinsic properties of the nanostructure. An important improvement in wear resistance is obtained for the coatings exhibiting the highest toughness and not the highest hardness. These results show that ion assisted processing is an effective tool for producing dense TiN-Ni nanocomposite coatings and tailoring their structure and mechanical properties.