Advanced Materials Research Vol. 214

Abstract: In recent years, considerable interest has developed in using fibers to increase the load-carrying capacity of concrete members. Fibers significantly reduce the brittleness of concrete and improve its engineering properties, such as tensile, flexural, impact resistance, fatigue, load bearing capacity after cracking and toughness. However, studies on the exact amount of influence are very limited. Among fibers, steel fibers are one of the most popular and widely used types of fibers in both research and practice. Steel fiber-reinforced concrete (SFRC) has been used increasingly in recent years and has a lot of applications. Previous researchers have mentioned that using fiber as 0.5 – 2.5 % of the volume of concrete can significantly improve the concrete properties. The purpose of this paper is firstly to investigate the effects of fiber volume on the compressive, splitting, and flexural behaviors of SFRC, and secondly to compare modes of failure. Variable items are the steel fiber volume fraction and the curing day. A series of 108 specimens (cube, cylinder and prism) with four different steel fiber volumes are used by a ratio of 0, 0.7, 1.0 and 1.5%. All specimens are cured in a water tank for 7, 14 and 28 days, respectively to provide same conditions. Hooked-ended steel fibers with a length of 30mm and a diameter of 0.75 mm are used.

Abstract: TiO2-AgCl/Cu2+ thin films containing 0 to 1%Cu2+ coated on glass slides were prepared by sol gel-dip coating method. The prepared films were synthesized at the temperature range of 100-500 °C. The microstructure and properties of synthesized TiO2-AgCl/Cu2+ thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy (DRS). Finally, the hydrophilic property was evaluated by means of contact angle of water droplet on the films. The results show that both calcinations temperature and Cu2+-doping have an effect on anatase and AgCl phase formation, crystallite sizes and phase content of the films. It was found that TiO2-AgCl/1%Cu2+ thin films calcined at 500 °C exhibit the highest photochromic (darken reaction) and self–cleaning effects (small contact angle) under UV irradiation.

Abstract: Edge detection directly affects the accuracy of image measurement. In this paper, focusing on the edge detection of the image of mechanical part polluted by hybrid noise consisting of Gaussian noise and impulse noise, an adaptive edge detection method is proposed. The proposed method combines a new hybrid filter smoothing noise adaptively with Canny operator to avoid the conflict of Canny operator between noise removing and edge locating, and uses Otsu threshold selection method to determine Dual-threshold of Canny operator adaptively. Using the gauge image polluted by hybrid noise as experiment object, the performance of the proposed method is evaluated qualitatively and quantitatively. Experimental results show that the proposed edge detection method has good performance.

Abstract: This work considers the effects of using the chitosan/sodium dodecyl sulfate (SDS) pretreated filters (CSPFs) as the antiseptic filters on the bioaerosol penetration. Three concentrations of chitosan solutions and chitosan/SDS mixing solutions were used to pretreat the polypropylene fibrous filter to make them antiseptic. The λ virus bioaerosol was generated using a Collison nebulizer, as the challenged bioaerosol. The effects of various factors, including the face velocity and the relative humidity on the bioaerosol collection characteristics were evaluated. Experimental results suggested the pretreatment of chitosan/SDS did have an antiseptic effect on virus bioaerosol and increase the inactivation mechanism. Experimental findings also revealed that the addition pretreatment of SDS did raise the inactivation effect of the chitosan. When adding SDS in the chitosan solution, the ammonium groups could appear and present the antiseptic benefit more obviously. Moreover, the antiseptic of the pretreated filter decreased with face velocity and RH.

Abstract: TiO2 varistors doped with 0.1 mol% Ta and different concentrations of CeO2 were obtained by ceramic sintering processing at 1400 °C. The effect of CeO2 on the nonlinear electrical behavior and dielectric properties of the Ta2O5-doped TiO2 ceramics were investigated. The nonlinear current (I)-voltage (V) characteristics of TiO2 are examined when doped with small quantities (0.1-0.9 mol%) of CeO2. It is found that CeO2 affects the electrical properties and the dielectric properties of the TiO2-based varistors. The samples have the nonlinear coefficients (α) values of (3.0-5.0), breakdown voltages (10-30 V/mm) and ultrahigh dielectric constants which is up to 105. A small quantities of CeO2 can improve the nonlinear properties of the samples significantly. It was found that an optimal doping composition of 99.4 mol% TiO2 - 0.1 mol% Ta2O5 - 0.30 mol% CeO2 was obtained with low breakdown voltage of 14.2 V/mm, high nonlinear constant of 4.5 , an ultrahigh electrical permittivity of 8.381.22×105 (measured at 1 kHz) and low tanδ of 0.32, which is consistent with the highest grain boundary barriers of the ceramics. The theory of defects in the crystal lattice was introduced to explain the nonlinear electrical behavior of the CeO2-doped TiO2-based varistor ceramics.

Abstract: The microstructure and nonlinear electrical behavior and dielectric properties of the varistor, which are composed of (Y2O3, Ta2O5)-doped TiO2 ceramics, were investigated for various sintering temperatures. It is assumed that the moderate sintering temperature improves the permitivity of TiO2 ceramics, together with high nonlinear properties. The varistor of 99.6 mol%-0.3 mol%Y2O3-0.1 nol%Ta2O5 composite sintered at 1400 °C has a maximal nonlinear coefficient of α =4.4, a low breakdown voltage of 10.8 V/mm, the ultrahigh electrical permittivity of 7.73× 104 and low tanδ of 0.34. The sintering temperature plays an important an important role on the nonlinear electrical characteristics and dielectric properties of the ceramics through its influences on the microstructure of samples.

Abstract: In order to enhance the density and decrease the sintering temperature，Al2O3/Si3N4 compound ceramics were sintered by pressureless using β- Si3N4 as raw materials and Al2O3 as sintering additives. The effects of Al2O3 as additive on the Vickers hardness and the sintering characteristic of Al2O3/Si3N4 compound ceramics were studied. The results shows that adding 9-15% nano- Al2O3 can get Al2O3/Si3N4 compound ceramics only in 1650°C by pressureless sintering because of nano- Al2O3’sintered. As a consequence, the relative density increases from 89% with micro alumina to above 97% with nano- Al2O3, the Vickers hardness increases from 1043.5MPa to 1356.0 MPa.

Abstract: Material that shows hydroxyapatite and β-tricalcium phosphate phases is called biphasic calcium phosphate (BCP). In present work, biphasic calcium phosphate was prepared and characterized for future applications on the utilization of bioactivity of HAp and resorbability of β-TCP properties. It was simply synthesized by precipitation method using eggshell as the calcium source (Ca) in the form of calcium nitrate and ammonium phosphate as the phosphate source (P) to obtain biphasic calcium phosphate. The prepared BCP powders and crystal structure were characterized by X-ray diffraction (XRD), Rietveld refinements and Fourier transform infrared (FT–IR) techniques. The results indicate that BCP was observed at the calcining temperature of 800 oC and above. Furthermore, the crystallinity of BCP increases with increasing temperature from 800 - 1200 oC. The phase fraction of β-TCP is enhanced with pH of a solution from 8.6-10.6 and decrease with the temperature range of 800 - 1200 oC. The formation of BCP arises from its non-stoichiometric composition of materials such as variation of synthesis parameters.

Abstract: This paper presents a non-linear numerical investigation of surface cracks in round bars under combined bending and torsion loadings by using ANSYS finite element analysis (FEA). Due to the non-symmetrical analysis, a full finite element (FE) model was constructed and special attention was given at the crack tip of the cracks. The surface cracks were characterized by the dimensionless crack aspect ratio, a/b = 0.6, 0.8, 1.0 and 1.2, while the dimensionless relative crack depth, a/D = 0.1, 0.2 and 0.3. The square-root singularity of stresses and strains was modeled by shifting the mid-point nodes to the quarter-point locations in the region around the crack front. The proposed model was validated with the existing model before any further analysis. The elastic-plastic analysis under the loading was assumed to follow the Ramberg-Osgood relation with strain hardening exponent, n = 5 and 10. J values were determined for all positions along the crack front and then, the limit load was predicted using the J values obtained from FEA through the reference stress method.

Abstract: This study presents a numerical investigation on the stress intensity factors (SIF), K of surface cracks in round bars that were obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node ¼-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed this proposed model validated for analyzing mode III problems. It was found that, the mode II SIF, FII and mode III SIF, FIII were dependent on the crack geometries and the sites of crack growth were also dependent on a/b and a/D.