Model-based inverse characterization of high-velocity tension impact failure in composites

This study presents the material characterization of high-velocity tension impact failure in composites using the split Hopkinson bar (SHB) test and the inverse analysis. A simulation code for the SHB test was developed using finite element analysis. In the code, the Hashin failure criterion is used to characterize the impact failure phenomena in composites. Material characterization is achieved to identify the material parameters for the Hashin criterion through inverse analysis from the measured strain histories during the SHB test. The advantage of this characterization is to obtain the true dynamic failure properties of composites without strict assumptions of elastic wave propagation on a specimen during the SHB test. Numerical examples are used to demonstrate the effectiveness of the present characterization.     

Membrane color and gas permeability of 6FDA‐TeMPD polyimide membranes prepared with various membrane preparation protocols

The relations among polyimide membrane colors, their gas transport and separation properties, and their fluorescence spectra were systematically investigated using fluorine‐containing aromatic polyimide, 6FDA‐TeMPD {[4,4‐(hexafluoroisopropylidene) diphthalic anhydride] [(6FDA)‐2,3,5,6‐tetramethyl‐1,4‐phenylene‐diamine (TeMPD)]}, which was used in electronic device and gas separation materials. Different molecular ordering structures of 6FDA‐TeMPD polyimides were prepared by controlling kinds of casting solvents and dry conditions. This difference was based on the effect of charge transfer (CT) interaction formed by π electrons of ring structures in polyimide. Membrane color measured using spectrophotometer determined colors as intrinsic parameters without sample collection. The permeability coefficients of oxygen and nitrogen of the 6FDA‐TeMPD polyimide membranes were correlated with membrane color index parameters such as L*, a*, b*, and ΔE*, and fluorescence properties such as maximum peak emission wavelength λ_max and intensity I_max, which reflect molecular ordering affected by CT interaction in polyimide membranes. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Modulation of Spin-Crossover Behavior in an Elongated and Flexible Hofmann-Type Porous Coordination Polymer

Three porous coordination polymers {Fe(dpa)[Pt(CN)₄]·G·nH₂O} (1-G; dpa = 1,2-di(4-pyridyl)ethane, G = dpa, bibenzyl (bbz) and stilbene (stb)) have been prepared by using a long and flexible ligand dpa. These compounds formed analogous 3-D elongated Hofmann-type frameworks based on 2-D planar layers extended by Pt–CN–Fe linkages with dpa as flexible pillar ligands. 1-dpa showed a characteristic three-step spin transition (ST) in the temperature range 180–240 K. The ST behavior was reversibly modulated by dehydration and hydration processes in keeping with the three steps. 1-bbz and 1-stb exhibited a gradual three-step ST over the range 80–200 K and an abrupt ST with T _c = 163 K. The guest-dependent cooperativity of the ST behavior is discussed by considering the flexibility of the framework and guest molecules.     

Thermal Behavior of Delithiated Li1−xMnPO4 (0 ≤ x <1) Structure for Lithium‐Ion Batteries

High‐voltage and high‐capacity cathode‐active materials are required to increase the energy density of rechargeable lithium‐ion batteries for hybrid vehicles. The olivine‐type LiMnPO₄ is considered as a good candidate for the next‐generation lithium‐ion battery due to its high voltage (4.1 V vs Li⁺/Li), low cost, and lower toxicity compared with the currently used layered materials. However, recent research has demonstrated that the thermal stability of delithiated phase of Li_1?xMnPO₄ (0 ≤ x <1) was less than that of Li_1?xFePO₄. These reports verified that the delithiated MnPO₄ decomposed and changed into Mn₂P₂O₇ with O₂ release at high temperature. In this study, we focused on the particle and crystal changes in LiMnP O₄/MnPO₄ at high temperature on a nanoscale. As a result, we have succeeded to observe directly the particle and crystal changes using transmission electron microscope (TEM) with heating. It revealed that MnPO₄ was a thermally unstable phase because dendrites of Mn₂P₂O₇ began to generate around 200°C.     

Iron‐Catalyzed Regio‐ and Stereoselective Conjugate Addition of Aryl‐Grignard Reagents to α,β,γ,δ‐Unsaturated Sulfones and its Synthetic Application

The iron‐catalyzed δ‐addition of aryl‐Grignard reagents to α,β,γ,δ‐unsaturated sulfones proceeded in a regio‐ and stereoselective manner to give cis‐4‐aryl‐2‐alkenyl sulfones. Allylic alkylation of the resultant products was performed without isomerization of the cis‐olefin to give cis‐4‐aryl‐1,1‐dialkyl‐2‐alkenyl sulfones, which upon intramolecular Friedel–Crafts reaction with aluminum chloride gave 1,4‐dihydronaphthalenes having a quaternary carbon center.     

Beam scattering of the Luneberg lens by a complex source point

The complex source point method and vector mode function expansion are used to calculate the electromagnetic beam scattering by the Luneberg lens. A six-layered medium with different radii is considered as a model of the Luneberg lens. A comparison between the well-known numerical result in the Cartesian coordinate system and the new numerical one in the vector mode function is made for the incident Gaussian beam propagation in free space. The propagation properties are in good agreement with each other. The total electric field distributions along the transversal and longitudinal axes are examined for scattering by the Luneberg lens, whose dimension is assumed to be comparable with the beam width. The focusing effect of the Gaussian beam is much lower than that of the plane wave. The spot size focused by the Luneberg lens almost equals the wavelength for the various beam parameters including the plane wave.     

Development of Microstructures of Long-Period Stacking Ordered Structures in Mg85Y9Zn6 Alloys Annealed at 673 K (400 °C) Examined by Small-Angle X-Ray Scattering

Development of LPSO structure and in-plane ordering during annealing the Mg85Y9Zn ternary alloy sample at 673 K (400 °C) was examined by synchrotron radiation small-angle scattering/diffraction measurements. By examining the first diffraction peaks for 18R, 10H, and in-plane order spot, the growth kinetics of in-plane order domain and the transition from 10H into 18R were discussed. The domain growth of in-plane order was characterized by small domain with little correlation between neighboring segregation layers.     

Enhanced multiobjective particle swarm optimization in combination with adaptive weighted gradient-based searching

This article proposes a new multiobjective optimization method for structural problems based on multiobjective particle swarm optimization (MOPSO). A gradient-based optimization method is combined with MOPSO to alleviate constraint-handling difficulties. In this method, a group of particles is divided into two groups—a dominated solution group and a non-dominated solution group. The gradient-based method, utilizing a weighting coefficient method, is applied to the latter to conduct local searching that yields superior non-dominated solutions. In order to enhance the efficiency of exploration in a multiple objective function space, the weighting coefficients are adaptively assigned considering the distribution of non-dominated solutions. A linear optimization problem is solved to determine the optimal weighting coefficients for each non-dominated solution at each iteration. Finally, numerical and structural optimization problems are solved by the proposed method to verify the optimization efficiency.     

Fabrication of fiber-reinforced functionally graded materials by a centrifugal in situ method from Al–Cu–Fe ternary alloy

Ternary Al–13.8at%Cu–1.6at%Fe alloy was prepared from Al–Cu and Al–Fe alloys at 1000 °C. The ternary Al–Cu–Fe alloy was centrifugally cast to fabricate a new type of functionally graded material (FGM) by a centrifugal in situ method. The structure is expected to differ from that of binary alloys. It was found that the fabricated FGM rings consist of four different phases, namely, Al, Al₂Cu, Al₇Cu₂Fe(ω) and Al₁₃Fe₄ phases. The shape of ω phase was fiber (needle) judging from the observation by a scanning acoustic microscope (SAM). The position dependence of the microstructure was examined on the fabricated FGM rings, and the volume fraction of ω phase was found to increase toward the outer region of the ring. Moreover, orientation and aspect ratio of the ω phase varied in the rings in a gradually graded manner. Therefore, the present study explores a method to produce fiber-dispersed FGMs by applying a centrifugal in situ method to ternary alloys.