Influence of Nb content on martensitic transformation and mechanical properties of TiNiCuNb shape memory alloys

In present work, microstructure, martensitic transformation behavior and mechanical properties of (Ti₅₀Ni₄₀Cu₁₀)_100−xNb_x (x = 0, 5, 10, 15 at.%) alloys were investigated as a function of Nb content. The addition of Nb to TiNiCu alloy leads to the presence of β-Nb phase. During cooling and heating, the alloys show one-step B2 ↔ B19 transformation. As the Nb content increases, the transformation temperatures almost linearly decrease and the transformation hysteresis monotonously increases due to the decrease of middle eigenvalue of the phase transformation matrix. The addition of Nb is effective in improving the elongation because of the introduction of β-Nb phase. With the increase of Nb content, both the yield strength and the critical stress to induce martensitic transformation increase, resulting in the improved superelastic strain.     

Hybrid algorithms for the twin–screw extrusion configuration problem

The twin-screw configuration problem (TSCP) arises in the context of polymer processing, where twin-screw extruders are used to prepare polymer blends, compounds or composites. The goal of the TSCP is to define the configuration of a screw from a given set of screw elements. The TSCP can be seen as a sequencing problem as the order of the screw elements on the screw axis has to be defined. It is also inherently a multi-objective problem since processing has to optimize various conflicting parameters related to the degree of mixing, shear rate, or mechanical energy input among others. In this article, we develop hybrid algorithms to tackle the bi-objective TSCP. The hybrid algorithms combine different local search procedures, including Pareto local search and two phase local search algorithms, with two different population-based algorithms, namely a multi-objective evolutionary algorithm and a multi-objective ant colony optimization algorithm. The experimental evaluation of these approaches shows that the best hybrid designs, combining Pareto local search with a multi-objective ant colony optimization approach, outperform the best algorithms that have been previously proposed for the TSCP.     

Graphite oxide intercalation compounds with rotator hexagonal order in the intercalated layers

Graphite oxide intercalation compounds (GOIC), exhibiting a large distance between graphite oxide sheets as well as a long-range order in the organization of guest species, are obtained by intercalation of organic cations containing two long hydrocarbon tails. In particular, graphite oxide layers with interlayer spacing of 0.84 nm, when ionically bonded with cations with two C18 chains, lead to GOIC with interlayer spacing of 3.4 nm and with a hexagonal rotator order in the packing of the long hydrocarbon tails. The intercalation of a second guest species with one or two long hydrocarbon tails not only leads to a further large increase of the interlayer spacing (from 3.4 nm up to 5.8 nm, for guests with C18 alkyl chains) but also, surprisingly, improves the order in the stacking of the layers as well as in the organization of the hydrocarbon chains in the interlayer space. X-ray diffraction measurements on powders and oriented films indicate that these ordered GOIC present intercalate structures with inclined and perpendicular bilayers of guest molecules. Differential scanning calorimetry associated with X-ray diffraction measurements show the occurrence of reversible loss of the hydrocarbon rotator order, which can be associated with significant changes of the interlayer spacing.     

VC and Cr3C2 doped WCoB-TiC ceramic composites prepared by hot-pressing

The grain growth inhibitors (GGIs) VC and Cr₃C₂ doped WCoB-TiC ceramic composites were fabricated by hot-pressing. The microstructure, hardness, transverse rupture strength (TRS), fracture toughness (K_IC) and wear-resistance of WCoB-TiC ceramic composites were investigated. The results reveal that the grains can obviously become refined and the densification temperature of WCoB-TiC ceramic composites will be increased due to the VC and Cr₃C₂. The typical microstructure of WCoB-TiC ceramic composites mainly consist of bright W₂CoB₂ grains, gray TiC particles, dark TiB₂ and pores. WCoB-TiC ceramic composites doped with 0.3 wt% VC and 0.3 wt% Cr₃C₂ hot-pressing at 1420 °C show the optimum mechanical properties (hardness, TRS and K_IC are 92.6 HRA, 1976 MPa and 14.8 MPa m^1/2, respectively) and the best dry sliding wear-resistance.     

The synthesis,electrochemical and theoretical nonlinear optical properties of push–pull chromophores for photorefractive composites

Four chromophores, of different dipole moment and polarizable anisotropy and which comprised conjugation bridges of both benzene and polyene with strong electron-donor and electron-acceptor groups, were characterized using ¹H NMR, FT-IR, UV–vis, and electrochemical analyses. The electric dipole moment (μ), polarizability (α) and the first hyperpolarizability (β) values of the chromophores were examined using computational methods. The contribution of orientational birefringence to total birefringence was estimated from the calculated molecular parameters of the chromophores; these parameters are important factors for predicting photorefractive efficiency.     

Modeling the Trans-Varestraint test with finite element method

The Trans-Varestraint test is modeled as three dimensional contact problem with finite element method (FEM). The local strains at the trailing of weld molten pool of samples with the Trans-Varestraint test are calculated under different bending strains. The calculated local strains are in good agreement with the experimental measurements. Meanwhile, the simulated results show that the maximum local strain on the top surface of the plate exceeds 5% in the brittle temperature range, obviously higher than the applied 1.5% average strain of the Trans-Varestraint test which is usually used as threshold of material resistance to the solidification cracks. As a result, it is suggested that the simulated local strains replace the average strains to represent the material resistance. At the same time, the comparison between the calculated driving force and the simulated material resistance predict the weld metal solidification cracking. It is therefore practicable that the local strains of the Trans-Varestraint test obtained with FEM replace the average strains to predict weld metal solidification cracking.     

Preparation of inorganic–organic pillared montmorillonite using ultrasonic treatment

Montmorillonite (Mt) is a clay mineral with expandable layer structure. Mesoporous pillared montmorillonite can be prepared by introducing gallery templates, such as simple metal cations, quaternary ammonium cations, long chain amines, and hydroxyed inorganic metal ions. In this paper, inorganic–organic pillared montmorillonite intercalated by aluminium and alkyl ammonium chloridize (HDTMA–Cl) was successfully prepared by ultrasonic treatment, and the physicochemical properties of the materials were systematically characterized by XRD, FT-IR, SEM and TEM techniques. The d₀₀₁ basal spacings and microstructures of Mt–Al–HDTMA were characterized by XRD. The function group, crystal surface morphology, structural and chemical analysis of Mt–Al–HDTMA were measured by FT-IR, SEM, TEM and EDX. The results indicated that ultrasonic method might accelerate the diffusion of the intercalating species, which enhanced the textural properties and the morphologies. The results also suggested that aluminium and HDTMA–Cl reagent entered the interlayer of Mt, and that the crystal structure of the final Mt was preserved.     

A one-step hydrothermal way for the synthesis of vanadium oxide nanotubes containing the phenylpropylamine as template obtained via non-alkoxide route

Vanadium oxide nanotubes (VO_x-NTs) with high crystallinity were synthesized by using the crystalline V₂O₅ as precursor for the first time with 3-phenylpropylamine as structure-directing template via one-step hydrothermal way. Structure and morphology of the nanotubes were investigated by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray powder diffraction, Thermal analysis and Infrared. The inner and the outer of the obtained nanotubes vary respectively between 15 to 25 nm and 70 to 100 nm with a length up to 4 μm.     

Fluorographene/polyimide composite films: Mechanical,electrical, hydrophobic,thermal and low dielectric properties

Nowadays, dielectric materials with excellent mechanical and hydrophobic properties are desired for use in the integrated circuits (ICs). For this reason, low dielectric constant fluorographene/polyimide (FG/PI) composite films were prepared by a facile solution blending method, suggesting that the mechanical, electrical, hydrophobic and thermal properties were significantly enhanced in the presence of FG. With addition of 1 wt% FG, the tensile strength, Young’s modulus and elongation at break were dramatically increased by 139%, 33% and 18% respectively when compared with pure PI film. Furthermore, composite films exhibit superior hydrophobic and thermal stability performance. Especially, the FG/PI film with 0.5 wt% of FG possessing a low dielectric constant of 2.48 and a good electrical insulativity that is lower than 10⁻¹⁴ S m⁻¹. Therefore, by their excellent performance, FG/PI hybrid films represent suitable candidate solutions with applications in the microelectronics and aerospace industries.     

A powerful estimation scheme with the error-in-variables-model for nonlinear cases: Reactivity ratio estimation examples

This paper gives an overview of the error-in-variables-model (EVM) procedure for parameter estimation with nonlinear models. It is shown that the nested-iterative EVM algorithm, used in this work, is efficient and powerful, since it provides both true values of the variables and the best estimates of the parameters. The step by step illustration along with evaluation techniques for results, are followed by further discussion about the importance and advantages of combining EVM with design of experiments strategies. With the focus on the performance of the EVM algorithm, an illustrative example of reactivity ratio estimation in copolymerization is included, with single-response (composition data) and multi-response (triad fraction data) scenarios.