Applied Mechanics and Materials Vols. 110-116

Abstract: Based on first principle FP-LAPW calculations, the electronic structure and magnetic properties of ZnO with Zn cation vacancy has been investigated. We find that the cation vacancy defect can induce a magnetic moment of about 2μB/supercell. The magnetic moment mainly comes from 2p-orbitals of O atoms which surround the Zn vacancy. We also find that the two Zn vacancies in ZnO always coupled Ferro-magnetically. Furthermore, the system shows half metallic Ferro-magnetic properties with high Curie temperature.

Abstract: Porous silica was prepared through TEOS sol-gel process catalyzed by acid-base joint catalyst, and the process was monitored by React IR^TM. Based on the measurements, mechanism of TEOS hydrolyzation and succedent condensation polymerization was inferred. Under acidic conditions, H⁺ attacks –OR group of TEOS firstly, then the electronegative Cl^- can attack Si⁴⁺ and make TEOS be hydrolyzed. When basic catalyst was added, the reaction will be accelerated. The promotion effect of base is attributed to the direct nucleophilic reaction mechanism and the smaller size of OH^-, which can attack Si more easily. Thirdly, silanol, generated from TEOS hydrolyzation, attract Si-OR or other Si-OH around; thereby resulting rapid dehydration or de-alcohol reaction. So the condensation polymerization rate is elevated, and Si-O-Si bond comes into being. Lastly, cross-linking reaction among Si-O-Si bonds forms the particle like conglomeration. The porous silica was characterized by SEM and N₂ adsorption-desorption technique. It was shown that the silica had large specific surface area, 818.5 m²/g, and relatively narrow distribution of pore size in meso-scale. Futhermore, the mesopores were nonuniform in shape and arrangement.

Abstract: CdS thin films deposited on glass substrate are prepared by chemical bath deposition using the reaction between CdSO₄ and CS (NH₂)₂. The composition, surface morphology and structural properties of as-deposited and annealed CdS thin films were studied using scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. The results indicate that the dense, homogeneous polycrystalline CdS thin films with smooth surface can be obtained by chemical bath deposition. The CdS thin films have cubic structure and the ratio of S and Cd is 1:1 in CdS thin films. Optical properties of CdS films were measured with ultraviolet-visible spectrophotometer. The optical band gap energy (Eg) of film sample was found to be 2.31 eV.

Abstract: A series of crystalline Ce1-xZrxO2 nanoparticles (where x = 0, 0.25, 0.5, 0.75 and 1.0) have been prepared by (i) hydrothermal (ii) polymer based metal-complex precursor solution reactions. Hydrothermal method was performed with diethanol amine as hydrolysis catalyst. The effect of reaction conditions on the size of particles and their morphology were investigated. In the polymer based method, by calcination of suitable polymer precursor solutions at a temperature range between 300 and 450 °C along with variation in the period of time, the metal oxide powders were subsequently obtained. The prepared powders have been characterized by powder X-ray diffraction (XRD), X-ray Fluorescence (XRF) .These studies reveled that zirconium is a good host for insertion into Cerium oxide in fluorite structure. The as-prepared samples were further characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average diameter of the nanoparticles were calculated from line broadening of XRD peaks and confirmed by SEM and TEM studies.

Abstract: In the present work, highly ordered TiO2 nanotube array with diameter were fabricated by one-step or two-step anodization of titanium foils. The prepared arrays were characterized by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). The photocatalytic activity of the TiO2 nanotube arrays was determined by degradation of X-3B under UV and compared to direct photolysis. The results showed that its photocatalytic activity in degradation of X-3B had been dramatically enhanced as compared to direct photolysis, and the photocatalytic performance of TiO2 nanotube arrays prepared by one-step anodization was better than that made by two-step anodization. Furthermore, adsorption performance analysis suggested that the higher catalytic activity of one-step nanotube array was attributed to its larger apparent maximum number.

Abstract: In this paper, an attempt has been made to mill constituent of WC and Co powder towards achieving volumetric percentage of WC (91%) and Co (9%). The ball milling technique was conducted under dry and wet condition using various milling parameters, rotation speed, time and ethanol as milling medium. Electron dispersive spectrometer (EDS) detected the elemental distribution, whilst SEM and particle size analysis was done to study the effect of changes in particle morphology and reduction of particle size. As a conclusion, powder milled by parameter of wet milling by ethanol, speed of rotation at 250 rpm and 90 minutes of milling time exhibits best results in term of volumetric percentage of 91%WC and 9%Co and particle size reduction.

Abstract: Prediction of sheet metal forming limits or analysis of forming failures is a very sensitive problem for design engineers of sheet forming industries. In this paper, first, damage behaviour of St14 steel (DIN 1623) is studied in order to be used in complex forming conditions with the goal of reducing the number of costly trials. Mechanical properties and Lemaitre's ductile damage parameters of the material are determined by using standard tensile and Vickers micro-hardness tests. A fully coupled elastic-plastic-damage model is developed and implemented into an explicit code. Using this model, damage propagation and crack initiation, and ductile fracture behaviour of hemispherical punch bulging process are predicted. The model can quickly predict both deformation and damage behaviour of the part because of using plane stress algorithm, which is valid for thin sheet metals. Experiments are also carried out to validate the results. Comparison of the numerical and experimental results shows good adaptation. Hence, it is concluded that finite element analysis in conjunction with continuum damage mechanics can be used as a reliable tool to predict ductile damage and forming limit in sheet metal forming processes.

Abstract: Reconfigurable Manufacturing Systems (RMS) have the potential to emerge as a cost effective solution that will help manufacturing organizations to stay competitive in an environment where product mix changes frequently and product life cycles are getting shorter. Reconfigurable Manufacturing Systems can achieve this as they are designed for quick changes in its configuration, as well as software and hardware components. This not only helps in accommodating production capacity but also production of new variety of products and introduction of new product within part family. However, the configurations have a significant impact on the productivity and reliability of the machines and the manufacturing system. In the present paper, the main objective is to present a framework consisting of Maintenance plan to be followed for the reconfigured machine, Reliability of the reconfigured machine, Quality of the product obtained. This framework can form as the basic idea and a link between maintenance, reliability and quality issues.

Abstract: The aim of this paper is to develop a functional-based stack-up design system for stamping dies. By performing function analysis, function decomposition, and geometric analysis, design engineers are able to identify a particular die’s functional features and their main variables, which are used as the basic units for the stack-up design. This stack-up design system includes a die design knowledge base, a functional feature module, and graphic user interfaces. A functional-based stack-up design system has been implemented on a Windows operation system through interfacing Visual Basic codes with commercial software, CATIA and Automation API. To showcase the power of the system, an example of designing a lower of the drawing dies for roof outer panels is provided. Based on the experimental results, the system is an efficient, flexible and accurate stack-up system for designing die structures.