Analytic investigation of effect of electric field on elasto-plastic response of a functionally graded piezoelectric hollow sphere

In this work, the effect of electric potential on the mechanical (Stresses, strains, displacement) and electrical (electrical displacement and intensity) response of a Functionally graded piezoelectric (FGP) hollow sphere is analytically investigated. The sphere is under the action of internal/external pressure and temperature gradient as well. The inhomogeneity is based on power law in radial direction. The analysis is done in two parts: elastic response and plastic response, using Tresca yield criterion. It is shown by illustrative example that under internal pressure and assumed model parameters, the commencement of plastic region is from outside surface towards inside in the plastic zone is extended with the increase of electric potential. Interestingly, radial stress and displacement have an extreme not on the boundaries, but on the inside.     

Effect of plate-like glass fillers on the mechanical properties of dental nanocomposites

In this study, glass flakes were incorporated into the spherical nanosilica component of the dental composites and its effect on the mechanical properties of these composites was investigated. To achieve a good interfacial adhesion between matrix resin and fillers, the particles were surface treated with a silane coupling agent (γ-MPS). Composites with different plate-like and spherical nanoparticle contents were prepared and their mechanical properties, including flexural strength, flexural modulus and fracture toughness were measured. The morphology of the particles and fracture surface of the composites were studied by SEM. The distribution of the flakes in the composite was also monitored using EDXA. Statistical analysis of the data was performed with ANOVA and the Tukey’s post hoc test was at a significance level of 0.05. The results showed that the flexural modulus and fracture toughness of specimens were improved with increasing the glass flake content up to 15 vol % which then declined upon further increase due to the stacking of the flakes on each other. A good interfacial adhesion was observed between matrix resin and particles in the SEM micrographs. The results of this study suggest that incorporation of glass flakes into the dental composites containing spherical nanosilica particles may enhance their mechanical properties.     

Effect of interface on mechanical properties and biodegradation of PCL HAp supramolecular nano-composites

This research explores the correlation between the structural properties of supramolecular biocomposites and their mechanical strength. Hybrid biocomposites composed of surface-modified hydroxyapatite nano-particles and supramolecular polycaprolactone (SP PCL), were prepared at different compositions, and their mechanical, thermal and viscoelastic properties as well as biodegradability, biocompatibility and cytotoxicity were evaluated in vitro. The results were compared with those for SP PCL/naked hydroxyapatite nano-composites. We show that surface modification of hydroxyapatite nanoparticles resulted in outstanding improvement of tensile strength and modulus up to 3.6 and 2.2-fold, respectively. At above 10 wt% HAp and 20 wt% HApUPy, heterogeneous nano-composites with inferior mechanical properties were obtained. Based on rheological (in steady shear mode) and small/wide angle X-ray scattering measurements, unusual improved mechanical properties were ascribed to the formation of supramolecular clusters around nanoparticles. In-vitro degradation of the supramolecular nano-composites was also studied to investigate the overall product biodegradation as well as toxicity of the degradation product(s).     

Stability of black, gray, and bright nonlinear guided waves in athin film bounded by a self-defocusing medium

Stability of nonlinear guided waves trapped in a thin linear film bounded by an infinite self-defocusing nonlinear medium is investigated. In addition to the trapped black and gray nonlinear guided waves, the existence of a novel class of bright nonlinear guided waves (with nonzero intensity background) is demonstrated. The gray and fundamental bright nonlinear guided waves are found stable whereas the black nonlinear guided waves are unstable to an asymmetric perturbation (but stable to a symmetric perturbation). The instability of the black nonlinear guided waves is shown to develop into various states, including stable gray and bright nonlinear guided waves, depending on initial excitations     

Stability of the asymmetric nonlinear mode trapped in symmetricplanar waveguides

The authors examine the reliability of the numerical approach for studying the asymmetric nonlinear mode trapped in a thin linear film sandwiched in an infinite self-focusing medium, and thus resolve a controversy in the literature on the stability of the mode trapped between the bifurcation point and the transition point on the dispersion curve reported. They demonstrate that as a result of the instability there exists a class of quasi-periodic solutions arising from the instability in the asymmetric mode on the unstable branch and weakly stable branch. In addition, the effect of loss on the propagation characteristics of the nonlinear mode is investigated. The evolution is shown to follow the dispersion curve adiabatically in the stable region provided the loss is small, whereas the initial excitation on the unstable branch leads to evolution away from oscillation around the dispersion curve     

A mixed analytical-numerical investigation of snap-through of low arches with a power-law variable thickness

Snap-through is an instability phenomenon that occurs in arch and dome-shaped structures, wherein the structure has to move from a stable equilibrium state through an unstable path into another stable equilibrated configuration in a jumping action. In this study, a linear elastic isotropic low arch is considered as a structure with power-law variable thickness. The phenomenon is investigated by considering the equation of the deflection for the variable thickness arch, solving it with an elegant analytical technique, and finding the snap-through critical load from an extreme condition. The effect of power-law exponent and geometry of the arch centerline on critical load is investigated and the constant thickness case and a very rare case of power-law thickness variation found in literature are considered for verification.     

Propagation of (2 + 1)-dimensional solitary waves in dissipative/active saturable nonlinear media

Abstract

We investigate the propagation of (2 + 1)D bright solitary waves in a saturable nonlinear medium perturbed with gain or loss. We find that in the presence of loss (gain) the amplitude and width of the (2 + 1)D bright solitary waves may both increase (decrease) with their product varying adiabatically during evolution. This is in contrast to the (1 + 1)D Kerr bright (dark) solitons or (2 + 1)D vortex solitons whose amplitude decreases (increases) at the same rate as the width increases (decreases), keeping their product unchanged with the propagation distance. For a very weak nonlinear saturation approaching Kerr nonlinearity, it is found that the amplitude and the width change at a rate faster than the (1 + 1)D Kerr bright and dark solitons, whereas their variation in highly saturable media is slower than the (1 + 1) or (2 + 1)D Kerr dark solitons. In a medium of moderate nonlinear saturation, the beam width and amplitude may vary in the way following that of high nonlinear saturation or weak nonlinear saturation or a combination of the two, depending on loss or gain and propagation distance.     

Physical and mechanical properties of nanocomposite barrier film containing encapsulated nanoclay

Waterborne poly(styrene‐co‐butyl acrylate) was prepared via miniemulsion polymerization in which nanoclay (Cloisite® 30B, modified natural MMT) in different concentrations was encapsulated. Scanning electron microscopy, X‐ray diffraction, and transmission electron microscopy confirmed the encapsulation and intercalated‐exfoliated structure of Cloisite® 30B within poly(styrene‐co‐butyl acrylate). The effect of nanoclay content on water vapor permeability, water uptake, oxygen permeability, thermal, and mechanical properties of thin films containing 1.5, 2.56, 3.5, and 5.3 wt % encapsulated Cloisite® 30B in poly(styrene‐co‐butyl acrylate) was investigated. The presence of encapsulated Cloisite® 30B within the polymer matrix improved tensile strength, Young's modulus, and toughness of the nanocomposites depending on the nanoclay content. Water vapor transmission rate, oxygen barrier properties, and thermal stability were also improved. The results indicated that the incorporation of Cloisite® 30B in the form of encapsulated platelets improved physicomechanical properties of the nanoclay‐polymer composite barrier films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis,Characterization and Properties of Novel Poly(urethane‐imide) Networks as Electrical Insulators with Improved Thermal Stability

Summary: A new series of thermoplastic poly(urethane‐imide)s (TPUI1‐4) containing hydroxyl groups in the backbone was synthesized from the reaction of epoxy‐terminated polyurethane prepolymers (EPU1‐4) and an imide containing diacid (DIDA) chain extender under optimized reaction conditions. EPU1‐4 was prepared through end‐functionalization of NCO‐terminated polyurethanes based on polyester polyol (CAPA) and hexamethylene diisocyanate with glycidol. A blocked isocyanate (BIC) was made from the reaction of trimethylol propane (TMP), toluene diisocyanate (TDI) and N‐methylaniline (NMA). Polymer networks were prepared from the reaction of librated isocyanate groups of BIC with hydroxyl groups of TPUIs. The starting materials and polymers were characterized by conventional spectroscopic methods and the physical, thermal and electrical properties of crosslinked networks were studied. Investigation of the recorded properties for these samples showed considerable improvement in thermal and electrical properties in comparison to common polyurethanes.

Synthetic route for preparation of TPUIs.