Surface-modified alumina nanoparticles-filled aramid fiber-reinforced epoxy nanocomposites: preparation and mechanical properties

Iranian Polymer Journal - Surface of Al2O3 nanoparticles was modified with a silane coupling agent, and aramid fiber-reinforced epoxy nanocomposites were produced using these particles. Three...     

The Numerical Analysis of Oscillating Rectangular Impinging Jets

In this study, the flow and heat transfer characteristics of oscillating air jets impinging on a flat surface were numerically analyzed. The jet velocity oscillated sinusoidally in time. A computer program, based on the control volume method and SIMPLE algorithm, was developed to numerically analyze the problem. Numerical simulations were performed to investigate the effects of the Reynolds number, amplitude, and frequency of the jet oscillation on the flow and heat transfer. It was observed that when the jet is oscillated, the Nusselt number moderately increases compared to the Nusselt number of steady jets.     

Producing NiCrAl alloy by the SHS method for use in thermal spray powder manufacturing

A series of Ni alloys containing 36.15–44.54 wt.% Cr and 2.0–13.50 wt.% Al was synthesized by Self-Propagating High-Temperature Synthesis (SHS) using a mixture of NiO, Cr₂O₃ and Al powders in order to obtain low-cost starting materials for thermal spray powder production. The experiments were carried out with the addition of an excess stoichiometric amount of Al between 0 % and 30 %. Additions of CaO and CaF₂ were also done to remove sulfur from the alloy and to investigate the effect on metal recovery. Thermochemical simulations of the SHS processes were examined with the FactSage program. The products were characterized by chemical analysis, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and microhardness techniques.     

Functional copolymer/organo-MMT nanoarchitectures: self-assembled core-shell morphology of poly(maleic anhydride-alt-α-olefin)/organo-MMT nanocomposites

This work describes the TEM morphology analysis of amphiphilic alternating copolymers of maleic anhydride (MA) with different α-olefins (1-hexene, 1-octene, 1-dodecene) synthesized by radical-initiated intercalative copolymerization of preintercalated MA···organoclay complexes in the presence of two types of organoclay such as reactive octadecyl amine-montmorillonite (ODA-MMT) and nonreactive dimethyldidodecyl ammonium-MMT (DMDA-MMT). TEM analyses of all the nanocomposites indicate the formation of symmetric or non-symmetric core-shell morphologies. Energy dispersive X-ray spectroscopy analyses were used to study the occurrence of the element in the poly(MA-alt-α-olefin)/organo-montmorillonite nanocomposites. A role of surfactant in these nanosystems insists on alternating copolymer segments with given hydrophobic/hydrophilic balance and surface organo-modifiers of MMT clays. Highly organized self-assembly with symmetric core-shell morphology were formed in nanosystems prepared in the presence of DMDA-MMT clay as compared with ODA-MMT clay-containing nanosystems. The relatively long branched olefin fragments significantly improve image parameters of core-shell morphology where some of the core structures contain accumulated and finely dispersed silicate particles at nano level around 2–25 nm. This observed phenomenon has brought a new approach for future utilization of these nanosystems in controlled drug delivery and anticancer applications with essentially prolonged activity.     

Shape memory behavior of FeNiCoTi single and polycrystals

We present experimental and theoretical evidence of thermoelastic martensites in Fe29Ni18Co4Ti alloys. In this class of alloys, the high strength in the austenite domains limits the slip deformation as verified with transmission electron microscopy. The restriction of slip permits a higher degree of recoverability of the transformation. Using both single crystals with [123] orientation and polycrystals, the appearance of martensite plates upon deformation, and their reversion back to austenite upon heating (the shape memory effect), is revealed with in-situ optical microscopy. Theoretical results for the transformation strains and the detwinning of martensite are presented, which demonstrate convincingly the potential of these classes of alloys. Electrical resistance measurements identified the stress and temperature levels at the onset of forward and reverse transformations in isothermal deformation and thermal cycling experiments, respectively. The return of the electrical resistance to its reference value, upon austenite to martensite followed by martensite to austenite transformation, verified the recovery in the transformation strains measured in the experiments.     

A comprehensive evaluation of parameters governing the cyclic stability of ultrafine-grained FCC alloys

The current paper presents results of a thorough experimental program undertaken to shed light onto the mechanisms dictating the cyclic stability in ultrafine-grained (UFG) alloys with a face-centered cubic structure. Cyclic deformation responses of several copper- and aluminum-based UFG alloys were investigated and the corresponding microstructural evolutions were analyzed with various microscopy techniques. The important finding is that a larger volume fraction of high-angle grain boundaries and solid solution hardening significantly improve the fatigue performance of these alloys at elevated temperatures and high strain rates, and under large applied strain amplitudes.     

Neonatal bladder rupture: an unusual complication of umbilical catheterization

Bladder injury in the neonatal period is an exceedingly rare phenomenon that is usually iatrogenic. Bladder rupture as a complication of umbilical catheterization in a newborn with urinary ascites, respiratory distress and hematuria is presented and discussed.     

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.