Flux-induced structural modification and phase transformations in a Pd40Ni40Si4P16 bulk-glassy alloy

In order to uncover the mechanism of fluxing-enhanced undercooling, a study of the liquid structure in a Pd₄₀Ni₄₀Si₄P₁₆ bulk-glassy alloy was performed, which revealed that a flux-treated sample presents a shortened mean interatomic distance and an increased coordination number within the first shell, which results in a more densely packed local structure than in an unfluxed sample. In addition to the usual influence of fluxing to effect a deactivation of nucleation catalysts to yield enhanced undercooling, structural studies have discovered a new effect of fluxing. The local structural change induced by fluxing is associated with an increase in the delay time for the onset of nucleation. The prolonged transient period is also reflected by sluggish atomic transport in the fluxed sample, which promotes kinetic stability of the undercooled liquid.     

Shear‐rate‐dependent rheology effects on mass transport and surface reactions in biomicrofluidic devices

Consideration is given to shear‐rate‐dependent rheology effects on mass transport in a heterogeneous microreactor of rectangular cross section, utilizing both numerical and analytical approaches. The carrier liquid obeys the power‐law viscosity model and is actuated primarily by an electrokinetic pumping mechanism. It is discovered that, considering the shear‐thinning biofluids to be Newtonian fluids gives rise to an overestimation of the saturation time. The degree of overestimation is higher in the presence of large Damkohler numbers and electric double layer thicknesses. It is also increased by the application of a favorable pressure gradient, whereas the opposite is true when an opposed pressure gradient is applied. In addition, a channel of square cross section corresponds to the maximum fluid rheology effects. Finally, the numerical results indicate the existence of a concentration wave when using long channels. This is confirmed by analytical solutions, providing a closed form solution for wave propagation speed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1912–1924, 2015     

An LO architecture with novel wide locking range,quadrature output RILFDs and ILROs for cognitive radio applications

In this paper, a wide locking range, quadrature output ring type injection locked frequency divider (ILFD) is presented for division ratios of 3 and 4. This ILFD proposes a novel injection scheme that shapes the injection signal to a proper form and provides a convenient situation for divider locking. Furthermore, two new wide locking range, low power consumption, injection locked ring oscillators (ILROs) are proposed for quadrature generation in local oscillator architectures. A novel cognitive radio quadrature local oscillator (LO) architecture is presented by utilizing the proposed ILFDs and ILROs to verify the effectiveness of the proposed circuits. Moreover, a new technique is implemented on the LO architecture to widen the frequency range without consuming any extra power. Because of using a single LC tank, this architecture is very compact. Also, it has the benefit of low power consumption and low output phase noise.     

FTIR and thermal analyses of intermolecular interactions in poly(trimethylene terephthalate)/phenoxy blends

Intermolecular interactions in the blends of poly(trimethylene terephthalate)/phenoxy resin of bisphenol A prepared by melt mixing in a microcompounder were studied using Fourier transform infrared (FTIR) spectroscopy and thermal analysis. The FTIR results revealed the characteristic bands of the blend constituents along with the bands showing interassociated, self‐associated, and nonassociated hydrogen bonding in the blends. It was found that the self‐associated hydrogen bonds in the blends were favorable over the interassociated bonds. On the other hand, using the melting point depression, the interaction parameter of the blends was calculated to be about 0.047. The positive value of the interaction parameter and low degree of interassociated hydrogen bonding in the blends suggest the immiscibility of the blends, which is confirmed by scanning electron microscopy observations as well as dynamic mechanical analysis. However, for chemically reacted compositions, the blends were changed to homogenous systems. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Investigation of exchange reactions and rheological response of reactive blends of poly(trimethylene terephthalate) and phenoxy resin

BACKGROUND: Reactive melt blends of poly(trimethylene terephthalate) (PTT) with a phenoxy resin (Ph) are some of the most interesting classes of reactive blends in which different kinds of exchange reactions can occur. This work is devoted to the study of these reactions and their effect on the rheological and morphological properties of the blends. RESULTS: The occurrence of transesterification reactions was confirmed by ¹H NMR analysis. Scanning electron microscopy observations confirmed that all the blends, except PTT/Ph 90/10 (w/w), which exhibits a droplet‐in‐matrix morphology, are homogeneous. At the beginning of transesterification, the melt viscosity of the blends is more influenced by molar mass increasing reactions than by molar mass decreasing ones. After extension of the reaction time and increase in temperature the molar mass reducing reactions become predominant, which results in a reduction of the complex viscosities. CONCLUSION: This work provides new data on the transesterification reactions involving the secondary hydroxyl groups of phenoxy. The properties of PTT/Ph blends are strongly determined by the transesterification reactions, which on the one hand results in the formation of PTT‐grafted phenoxy chains and on the other hand a decrease in the molar mass of non‐bonded PTT. These reactions exert a distinct compatibilizing effect between the blend components. Copyright © 2008 Society of Chemical Industry     

A magnesium alloy matrix composite reinforced with metallic glass

Novel light-weight materials of advanced performance are now experiencing global interest due to the strong need to reduce energy consumption in land and air transportation sectors. Here we report on a novel magnesium alloy matrix composite material. The reinforcing phase in the magnesium alloy is a fine dispersion of metallic glass particles. The composite is sintered from the powder mixture of the alloy and metallic glass at a temperature slightly above the glass transition T_g of the metallic glass particles that is close to the Mg alloy’s solidus temperature. At the compaction temperature, the metallic glass acts as a soft liquid-like binder but upon cooling it becomes the hard reinforcement component of the composite. Processing, microstructure and mechanical properties of the composite are discussed.     

Estimating terminal velocity of rough cracks in the framework of discrete fractal fracture mechanics

In this paper we first obtain the order of stress singularity for a dynamically propagating self-affine fractal crack. We then show that there is always an upper bound to roughness, i.e. a propagating fractal crack reaches a terminal roughness. We then study the phenomenon of reaching a terminal velocity. Assuming that propagation of a fractal crack is discrete, we predict its terminal velocity using an asymptotic energy balance argument. In particular, we show that the limiting crack speed is a material-dependent fraction of the corresponding Rayleigh wave speed.     

Wind-Turbine Gear-Box Roller-Bearing Premature-Failure Caused by Grain-Boundary Hydrogen Embrittlement: A Multi-physics Computational Investigation

To help overcome the problem of horizontal-axis wind-turbine (HAWT) gear-box roller-bearing premature-failure, the root causes of this failure are currently being investigated using mainly laboratory and field-test experimental approaches. In the present work, an attempt is made to develop complementary computational methods and tools which can provide additional insight into the problem at hand (and do so with a substantially shorter turn-around time). Toward that end, a multi-physics computational framework has been developed which combines: (a) quantum-mechanical calculations of the grain-boundary hydrogen-embrittlement phenomenon and hydrogen bulk/grain-boundary diffusion (the two phenomena currently believed to be the main contributors to the roller-bearing premature-failure); (b) atomic-scale kinetic Monte Carlo-based calculations of the hydrogen-induced embrittling effect ahead of the advancing crack-tip; and (c) a finite-element analysis of the damage progression in, and the final failure of a prototypical HAWT gear-box roller-bearing inner raceway. Within this approach, the key quantities which must be calculated using each computational methodology are identified, as well as the quantities which must be exchanged between different computational analyses. The work demonstrates that the application of the present multi-physics computational framework enables prediction of the expected life of the most failure-prone HAWT gear-box bearing elements.