Advanced Materials Research Vol. 428

Abstract: The main goal of this research is studying the crystal structure and formation of both free radicals and trapped space charges in the pure and doped polyvinylidene fluoride (PVDF) films with various concentrations of transition metal halides TMHs (AlCl₃, ZnCl₂, and CoCl₂). Electron Spin Resonance (ESR) was used to detect the existence of free radicals and the probable magnetic interactions between the halide and PVDF. The hyperfine splitting of the ESR was used to study the electronic structure of the existence radicals. Thermally stimulated dielectric response measurements have been made using Frequency Resolved Dielectric Spectroscopy (FRDS). This was useful for studying the formation and trapping of the space charge to enhance the results obtained by ESR. The new crystalline structures and the complex compounds which may be developed due to the chemical reaction between the polymer and the added halides were analysid.

Abstract: Based on the constitutive relationship model of general concrete filled steel tube, and combining with the results and theoretical analysis of several self-stress concrete filled steel tubular specimens, the constitutive relationship model of self-stress concrete filled steel tube was established by introducing an improvement coefficient of concrete strength related to self-stress level. The calculations of specimens’ bearing capacity with different sectional steel ratios, values of self-stress and concrete strengths were performed, which were in a good accordance with those of experimental values.

Abstract: According to the requirement of specification that steel tube of concrete filled steel tubular (CFST) arch bridge should be among elastic state in service stage, this paper obtained a maximum limit value of steel tube circumferential stress.Then based on the Von Mises yield criterion and principle of static equilibrium, the formula of the circumferential stress of steel tube and self-stress of concrete was built. The equation of restrained expansion rate and self-stress of concrete in accordance with general stress-strain relationship was established. The reasonable scope of self-stress should be controlled in MPa, which could ensure to reach the restrained expansion rate of concrete in closed condition.

Abstract: The real structures are of complex geometrical forms containing numerous zones of stress concentrations. These sites are characterized by weak sections due to the presence of notches which are the main causes of cracks initiation. The knowledge of the distribution of the stress field in the neighborhood of a notch is of an extreme importance for the analysis of the variation of the stress concentration factor with respect to the geometry of the notch. In this paper, the finite element method is used to study the effect of the existence of a microcrack on the behaviour of a notched structure. Then the behaviour of a crack emanating from the notch with the presence of the pre-existing crack is also investigated. It requires estimating the stress intensity factor at the crack tip, the length of the crack, the notch diameter and the angle between its bisecting line and the crack direction.

Abstract: Ceramic/metal bimaterials systems are increasingly used in industry owing to the synergetic association of opposite properties of the bonded materials. Discontinuity in these properties can result in crack initiation and stress concentration entailing the bimaterial system failure. A good understanding of damage mechanism at the metal/ceramic interface is crucial to the dimensioning of multilayered systems. In this work the finite element method is used to analyze the stress concentration effect in a linear interface and curved interface. The geometrical configuration of the interface has a great influence the stress concentration on distribution developed near or in the assembly interface. The effect of a circular notch on the behavior of an interfacial crack is highlighted. The results indicate that the interface generates normal and tangential stress concentration resondless of the assembly mechanical properties. The curved geometry of the interface strongly reduces stress concentration in comparison with the linear interface. The reduction is 90%.

Abstract: In this study the effects of milling methods on particle size and phase transformation of strontium and nickel doped lanthanum chromite as an interconnect material for solid oxide fuel cells (SOFC) were investigated. Two compositions of La_0.9Sr_0.1Cr_0.9Ni_0.1O₃ (LS10N10) and La_0.7Sr_0.3Cr_0.9Ni_0.1O₃ (LS30N10) were synthesized by glycine nitrate process (GNP). The samples were characterized by means of X-ray diffraction, nitrogen adsorption–desorption, scanning and transmission electron microscope and laser particle size analyzer. Two different milling methods were used, namely, high-energy milling (HEM) and ball milling (BM) and the effects of these milling methods of as-synthesis powders on the particle size distribution, agglomeration behavior and phase transformation were also investigated. The results showed that BM caused reduction of particle size to submicron size with D50 value of 125 nm while HEM resulted in agglomeration. The obtained nanopowders, according to XRD results were single phase with perovskite type crystal structure and only in high content of Sr some SrCrO₄ was detected. HEM caused the dissolution of the second phase in LS30N10.

Abstract: Present investigation is devoted to study the effects of aqueous solution of 3.5% NaCl on high-cycle stress life and fatigue crack growth behavior of 7475-T7351 alloy. At low alternating stress the environment test exhibited corrosion pit dominated crack initiation and at high stress level crack initiation occurred through anodic dissolution. Corrosive environment resulted reduction in fatigue life, crack growth rate enhancement and drop in stage-I to stage-II transition. The behavior is explained with the help of fractographic observations.

Abstract: Fused Deposition Modeling (FDM) is one of the most popular Rapid Prototyping (RP) techniques. Initially used as means of producing 3D prototypes aiding in rapid product development, FDM found a significant application in medical models and with machine and material improvements is currently destined to be a true manufacturing process, challenging some of the traditional approaches. The material characteristics and part qualities however, are inferior, considering the heterogeneous structures characterized by the air gaps resulting from raster orientations. Current research is focused on improving the mesostructure through appropriate deposition schemes, adaptive slicing being one of the approaches. This paper reviews some of the adaptive slicing schemes and discusses software and hardware developments undertaken for the practical implementation of one of the schemes for producing test parts.

Abstract: Shape memory thin films deposited by sputtering are attractive candidates for micro-electro-mechanical-system (MEMS) because of their large deformation and strong recovery force. In the present study Ni-Ti thin films have been deposited on NaCl substrates by DC magnetron sputtering source fitted with an 80mm diameter alloy target. In order to obtain a variety of film compositions, several discs of alloy target, which prepared in vacuum arc remelting (VAR), were used. Three types of thin films have been deposited; Ti and Ni-rich thin films were separately deposited on NaCl substrate and also a composite layer of Ni45Ti50Cu5 and Ni-rich. The as deposited Ni-Ti thin films were crystallized to change the amorphous structure to a nanostructured material to characterize shape memory and superelastic behaviors. The effect of composition on film structure and mechanical behavior was studied by using X-ray diffraction (XRD) and nanoindentation. The results of thin films behavior were used to calculate the thickness ratio of be-layer composite NiTi to obtain enhanced shape memory behavior.

Abstract: This paper systematically studies the distribution of macro-particles on the surface of film influenced by the substrate position under conditions of the same magnetic field, different pulsed bias voltage and reaction gas partial pressure, and analyzes the mechanism of macro-particles influenced by different parameters. This study indicates that the substrate position has a better effect on decreasing macro-particles than that of the pulsed bias voltage and particles in different substrate position are very different in their forms and appearances, which easily leads to uneven deposition; under the same bias, the number of particles firstly increases and then decreases with the increasing the distance from substrate position to the center, and the number of particles with over 2μm diameter largely decreases with the increasing the distance from substrate position to the center, so surface morphologies of films are improving; under the lower intensity of magnetic field, the distribution of macro-particles has a great change with the increasing the distance from substrate position to the center, and under the higher intensity of magnetic field, the substrate position has little influence on the distribution of macro-particles on the surface of film. Under the higher intensity (30G) of magnetic field, the distribution of macro-particles on the surface of film has minor change whatever reaction gas partial pressure and substrate position increase, and most particles are small in sizes and are solid spherical in shape. The higher intensity (30G) of magnetic field enhances the uniformity of film deposition and decreases the dependency of macro-particles distribution on other parameters.