Numerical Investigation of the Macroscopic Mechanical Behavior of NiTi-Hybrid Composites Subjected to Static Load–Unload–Reload Path

Shape memory alloys (SMAs) are a type of shape memory materials that recover large deformation and return to their primary shape by rising temperature. In the current research, the effect of embedding SMA wires on the macroscopic mechanical behavior of glass–epoxy composites is investigated through finite element simulations. A perfect interface between SMA wires and the host composite is assumed. Effects of various parameters such as SMA wires volume fraction, SMA wires pre-strain and temperature are investigated during loading–unloading and reloading steps by employing ANSYS software. In order to quantify the extent of induced compressive stress in the host composite and residual tensile stress in the SMA wires, a theoretical approach is presented. Finally, it was shown that smart structures fabricated using composite layers and pre-strained SMA wires exhibited overall stiffness reduction at both ambient and elevated temperatures which were increased by adding SMA volume fraction. Also, the induced compressive stress on the host composite was increased remarkably using 4% pre-strained SMA wires at elevated temperature. Results obtained by FE simulations were in good correlation with the rule of mixture predictions and available experimental data in the literature.     

Reduction of fossil fuel emissions in the USA: A holistic approach towards policy formulation

In the United States, the response of the federal government to the global initiative of reduction of emissions of CO₂ has been limited. With the Kyoto Protocol having entered into force in February 2005, there will be renewed international pressure on the United States for action. Concurrently, the US economy, growing modestly, is characterized by large current account and budget deficits. This situation calls for garnering additional revenue through repealing of the recent tax cuts. An option available is to impose a modest carbon tax. The rationale of such a tax is that it would address the twin objectives of additional revenue and reduction of emissions.     

Effects of metal source in metal substitution of lithium manganese oxide spinel

Usefulness of W substitution for improvement of battery performance of LiMn₂O₄ cathode was investigated. Small amounts of tungsten were incorporated into LiMn₂O₄ spinel instead of available Mn. For this purpose, two sources of tungsten (metallic W or WO₃) were examined. W concentration and source have significant influence on both morphology and electrochemical behavior of W-substituted LiMn₂O₄ spinels. W substitution of LiMn₂O₄ spinel can lead to the formation of uniform spinel particles and improved battery performance. Cyclic voltammetric behaviors of the samples were examined in an aqueous solution, and Li diffusion process was investigated for different cases. The best case was the LiW_0.01Mn_1.99O₄ spinel prepared from metallic W powder, as exhibits excellent rate capability, but better cycleability was observed for the LiW_0.01Mn_1.99O₄ spinel prepared from WO₃. This means that because of significant influence of the dopant source, this parameter should be chosen in respect with the desire improvement.     

Preparation,characterization and mechanical properties of controlled porous gelatin/hydroxyapatite nanocomposite through layer solvent casting combined with freeze-drying and lamination techniques

In this present study, to mimic the mineral and organic component of natural bone, hydroxyapatite (HA) and gelatin (GEL) nanocomposite was prepared via layer solvent casting combined with freeze-drying and lamination techniques. Glutaraldehyde (GA) was used as cross-linking agent. The synthesized nanocrystalline hydroxyapatite and nanocomposite samples were characterized by the commonly used bulk techniques. The results showed that GEL/HA nanocomposite were porous with 3-dimension interconnected microstructure, pore sizes were 100 μm to 1 mm, porosity were 75% to 93% and HA particles are dispersed evenly among gelatin fibers. It was also found that increasing initial GEL concentration and HA content enhance the elastic modulus (E) and reduce toughness and affect pore size and morphology. Finally, the stress–strain behavior in compression was very similar to natural spongy bone where the compressive modulus obtained was about 180 MPa.     

Response of a planar solid oxide fuel cell to step load and inlet flow temperature changes

To explore the dynamic characteristics of the SOFC systems and to develop relevant control strategies, a previously developed steady state SOFC model is converted to a dynamic model. The model includes mass, momentum, thermal and electrochemical analysis, as well as the kinetic model of hydrocarbon reactions. Applying two control strategies i.e., cell constant fuel flow rate and constant fuel utilization during the transient time, the model is implemented to analyse the dynamic behaviour of a planar direct internal reforming (DIR) SOFC cell under several step-load changes. Transient response, resulting from an inlet temperature variation, is also investigated. The results show that the relaxation time is strongly related to the thermal behaviour of the cell and the applied control strategy. However, it is almost independent of the load variation magnitude.     

A kinetic study on the electrophoretic deposition of hydroxyapatite–titania nanocomposite based on a statistical approach

In the present study, the electrophoretic deposition (EPD) process of hydroxyapatite–titania nanocomposite was kinetically described by the use of response surface methodology (RSM). The electrostatic interaction between particles in ethanol based suspensions was determined by Zeta potential and particle size analyses. After successful electrophoretic deposition from hydroxyapatite–titania suspensions with 0, 10 and 20 wt% of titania nanoparticles, it was shown that Baldisserri model can well reproduce the experimental data among the other semi-empirical kinetic equations. The as-deposited hydroxyapatite–titania nanocomposites were characterized employing SEM, AFM, XRD, and FT-IR analyses. Then, the effects of deposition voltage, deposition time and wt% TiO₂ on the kinetic of EPD at two time intervals (10–60 s and 60–300 s) were identified and quantified via RSM based on a central composite design (CCD). According to the results obtained from the statistical analysis, it was found that the deposition rate decreases by an increase in wt% TiO₂ and time. Also, a transition in deposition mechanism from linear to parabolic mode was observed and two second order polynomial equations were fitted to the response (deposit weight) at each time intervals.