The basic trait in the ceramics is their high brittle or low fracture toughness, and the main criteria in the design and application is specifying the fracture toughness in ceramics. In this paper, a new method is proposed to determine the fracture toughness of ceramics, which is enhanced in lowering the cost of fracture toughness determination relative to the previous methods. Hence due to the low cost and case of access of alumina (Al2O3) which is extensively used in ceramics industry, it is applied as the most important source for achieving the objectives. Pure alumina has excellent properties such as refractory and high hardness on one hand, and has disadvantages such as low fracture toughness on the other hand. In order to improve its mechanical properties, various additives such as nano scale silicon carbide (SiC) powder are used. In this paper, alumina micro powder having 5% nano magnesium oxide by weight were mixed separately with silicon carbide nano particles of 2.5%, 5%, 7.5%, 10% and 15% to construct various types of ceramics, with different physical and mechanical properties. Semi experimental equation for their fracture toughness determination was presented and used for other brittle materials. This equation has minimal cost of experiments for determining fracture toughness of different brittle materials. تفاصيل المقالة

Abstract: In this study, Al2O3–SiC nanocomposites have been fabricated by mixing of alumina powder containing 0.05% weight magnesium oxide and silicon carbide nano powders, followed by hot pressing at 16500C. The mechanical properties of Al2O3-SiC nanocomposites containing different volume fraction (2.5, 5, 7.5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. The MgO additive was able to promote the densification of the nanocomposites. Al2O3-SiC powders were prepared by planetary milling in isopropanol. The fracture mode and microstructure of specimens was investigated by means of scanning electron microscopy. The nanocomposites were tougher compared to alumina when they were hot pressed at the same temperature. The young’s modulus is decreased by increasing the volume percent of SiC. The values hardness and fracture toughness of the nanocomposites is increased by increasing the volume percent of SiC up to 7.5% and then decreased slightly. The ballistic energy dissipation ability is decreased by increasing the volume percent of SiC up to 5% and then increased slightly. The Scanning electron microscopy observations showed that fracture mode is changed from intergranular for alumina to transgranular for nanocomposites. It also shows the growth of grain is decreased by increasing the volume fraction of SiC particles. Finally X-ray diffraction analysis indicated that there was no chemical reaction between Al2O3 and SiC particles. تفاصيل المقالة

In this paper, experimental results of a deep drawing processto produce a cylinder of high strength steel with a spherical head were compared with it’s simulation results and three proposal design types. Meanwhile, the amount of limiting draw ratio in some stages was determined. Accuracy and precision of the results of a finite element software to predicting the multi stage deep drawing process of high-strength thin steel sheets was measured. ABAQUS version 6-9-3 was used to simulate the process. In this research, the raw material was a circular blank of annealed steel AISI-4130 with 2 mm thickness that in experimental test, subjected to one drawing stages, three redrawing stage and two heat treatment stages. The uni-axial tensile test was performed to determine the mechanical properties of the steel sheet. Numerical thickness distribution was compared with the experimental results in different stages of deep drawing and the accuracy was good (about 2.55%). Base on this results the proposal designs were simulated to introduce the properties of the most suitable design types. تفاصيل المقالة

In this paper, buckling of orthotropic rectangular plates under different loadings was investigated. For this reason, governing buckling equations for an isotropic plate were modified by applying constitutive equations of orthotropic materials. After obtaining the equations of orthotropic plates, Generalized Differential Quadrature method (GDQM) was applied on buckling equations and thus a set of Eigen value equations resulted. In order to solve this Eigen value problem, a computer program was developed using MATLAB software in a way that the influence of different parameters such as length to width ratio (aspect ratio), the number of layers, the angle of layers arrangement, material of layers, kind of loading and boundary conditions were included. A buckling load factor was calculated for simply supported and clamped supported plates. The results of GDQ method were compared with reported results from Rayleigh – Ritz method and with results from solving the Finite element using ANSYS 8.0 software. The comparison showed the accuracy of obtained result clearly. تفاصيل المقالة