Polymer ferroelectret based on polypropylene foam: piezoelectric properties prediction using dynamic mechanical analysis

Thin polypropylene (PP) foam films were produced by continuous extrusion using supercritical nitrogen (N₂) and then charged via corona discharge. The samples were characterized by dynamic mechanical analysis as a simple method to predict the piezoelectric properties of the cellular PP obtained. The results were then related to morphological analysis based on scanning electron microscopy and mechanical properties in tension. The results showed that the presence of a nucleating agent (CaCO₃) substantially improved the morphology (in terms of cell size and cell density) of the produced foam. Also, an optimization of the extrusion (screw design, temperature profile, blowing agent, and nucleating agent content) and post‐extrusion (calendering temperature and speed) conditions led to the development of a stretched eye‐like cellular structure with uniform cell size distribution. This morphology produced higher storage and loss moduli in the machine (longitudinal) direction than for the transverse direction, as well as higher piezoelectric properties. The morphological and mechanical results showed that higher cell aspect ratio led to lower Young's modulus, which is suitable to achieve higher piezoelectric properties. Finally, the best quasi‐static piezoelectric d₃₃ coefficient was 550 pC/N for a cellular PP ferroelectret having a uniform eye‐like cellular structure using N₂ as the ionizing gas inside the cells, while the highest value was only 250 pC/N when air was used. Hence, the value of d₃₃ can be improved by more than 100% just by replacing air with N₂ as the ionizing gas. Copyright © 2016 John Wiley & Sons, Ltd.     

Optical limiting behavior of disperse red 1 dye doped polymer

Measurements of optical limiting response in disperse red 1 dye doped into ethylene propylene diene polymethylene polymer (EPDM) are reported using 532 nm wavelength, 10 ns pulses from a frequency-doubled Nd-YAG laser. The optical limiting behavior of the dye doped polymer was studied by transmission measurement technique at various concentrations. The results reveal that the optical limiting efficiency is dependent on concentration.     

On the use of immersed boundary methods for shock/obstacle interactions

This paper describes the implementation of immersed boundary method using the direct-forcing concept to investigate complex shock–obstacle interactions. An interpolation algorithm is developed for more stable boundary conditions with easier implementation procedure. The values of the fluid variables at the embedded ghost-cells are obtained using a local quadratic scheme which involves the neighboring fluid nodes. Detailed discussions of the method are presented on the interpolation of flow variables, direct-forcing of ghost cells, resolution of immersed-boundary points and internal treatment. The method is then applied to a high-order WENO scheme to simulate the complex fluid–solid interactions. The developed solver is first validated against the theoretical solutions of supersonic flow past triangular prism and circular cylinder. Simulated results for test cases with moving shocks are further compared with the previous experimental results of literature in terms of triple-point trajectory and vortex evolution. Excellent agreement is obtained showing the accuracy and the capability of the proposed method for solving complex strong-shock/obstacle interactions for both stationary and moving shock waves.     

A NEW SELF-ADAPTIVE ITERATIVE METHOD FOR GENERAL MIXED QUASI VARIATIONAL INEQUALITIES

The general mixed quasi variational inequality containing a nonlinear term φ is a useful and an important generalization of variational inequalities. The projection method can not be applied to solve this problem due to the presence of nonlinear term. It is well known that the variational inequalities involving the nonlinear term φ are equivalent to the fixed point problems and resolvent equations. In this article, the authors use these alternative equivalent formulations to suggest and analyze a new self-adaptive iterative method for solving general mixed quasi variational inequalities. Global convergence of the new method is proved. An example is given to illustrate the efficiency of the proposed method.     

A version of Wiener’s and Lévy’s theorems

We obtain weighted algebra analogues of the classical theorems of N. Weiner and P. Lévy on absolutely convergent Fourier series      

Results of Vidav-Palmer Type in m-Convex Algebras

Using the notion of a normal cone, we give results of Vidav-Palmer type in terms of hermitian, quasi-hermitian and uniformly quasi-hermitian elements. Consequences are also given.     

Microporous membranes obtained from polypropylene blends with superior permeability properties

A blend of two polypropylene resins, different in molecular structure, one with linear chains and the other with long chain branches, was investigated to develop microporous membranes through melt extrusion (cast film process) followed by film stretching. The branched component significantly affected the row‐nucleated lamellar crystalline structure in the precursor films. The arrangement and orientation of the crystalline and amorphous phases were examined by wide angle X‐ray diffraction and Fourier transform infrared spectroscopy methods. It was found that blending of a small amount of a long chain branched polypropylene improved the orientation of the both crystalline and amorphous phases in the precursor films. Annealing, followed by cold and hot stretching were consequently employed to generate and enlarge pores in the films as a result of lamellae separation. SEM micrographs of the surface of the membranes obtained from the blend revealed elongated thin fibrils and a large number of lamellae. The lamellae thickness for the blend was much shorter in comparison to that of the linear PP precursor film. The permeability of the samples to water vapor and N₂ was significantly enhanced (more than twice) for the blend system. The porosity of the blend membrane showed a significant improvement with a value of 53% compared to 41% for the linear PP membrane. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 148–157, 2008     

Calcul harmonique dans les Algebres de Banach Hermitiennes

We introduce the use of a harmonic functional calculus in the generalized discussion of theorems of von-Neumann, ky Fan; and their extended versions.     

An elastic-perfectly plastic model for simulating an aluminum particle behavior during plasma thermal spraying using the finite element method

It is a 2D numerical study which treats the splat and flattening of the droplet during a thermal spraying process. An aluminum particle at a high temperature is impacted on steel substrate. A perfectly elastic-plastic model is used instead of the VOF method which is exclusively used in the literature. For this purpose, the finite element method with Ansys mechanical APDL program is used to solve the governing equations. Displacement, elastic and plastic strains, Von-Mises stress, energy densities, and contact pressure are evaluated during the impact of the particle. Additionally, it is found that the initial impact velocity has a significant effect on splat behavior. This mechanical model gives a promise results that can be improved to help understand the impact and flattening phenomenon.