AMIRKABIR
Year:2007 | Volume:18 | Issue:66-C|Papers Count:16

Improvement of properties of gypsum and gypsum/perlite products by glass-fiber and polyvinyl acetate was studied in this research. The proper type and grade of fiber and polymer was determined by preliminary tests. Different formulations were mixed and various tests were carried out on them, including the mechanical, thermal and acoustical and the resistance of samples against high temperature. The results show that the addition of perlite to gypsum improves the resistance of product against high temperature. In addition, the sound reduction of gypsum/perlite boards is reasonable and nearly same as gypsum boards. The results also shows that the mechanical properties of gypsum and gypsum/perlite products can effectively improved by addition of glass-fiber and PVA emulsion.

This paper proposes a rigorous method of three-dimensional slope stability analysis for convex slopes in plan view based on the upper-bound theorem of limit analysis approach and discusses about the effect of plan curvature on the stability of convex slopes. A rigid-block 3-D translational collapse mechanism is considered, with energy dissipation taking place along planar velocity discontinuities. This mechanism is optimized to obtain the minimum factor of safety for stability of the slope or to obtain the bearing capacity of rectangular foundations located on such slopes. Based on comparisons with the known solutions, the method was generally found to be accurate in predicting the stability of convex slopes. The results show that the stability of convex slopes in plan view is more than the stability of slopes obtained by 2D analysis. Dimensionless diagrams for various parameters are also presented.

Underground structures, such as tunnels and caverns are of paramount importance among the civil structures. Due to the complexity of these structures and lack of advanced and accurate models in rock mechanics field, underground structures are designed approximately and with a high safety factors. Therefore, such projects become more expensive and less economics. Applying fracture mechanics models in this respect may be resulted in more benefits. In this paper, smeared crack model has been applied to predict rock failure. In order to illustrate the performance and integrity of the model three-point flexural tests were carried out on cylindrical rock specimens. OOFEM computer program with the ability of analyzing fracture mechanics models was used for test results analysis. The results show a very good agreement between the test results. and the numerical analysis. To obtain the model parameters corresponding to the rock specimens tested, sensitivity analysis were performed on the each of the model parameters and a series of Brazilian tests were also carried out in this respect.

Dynamic properties of Shahid Rajaee Concrete Arch Dam were identified by forced vibration tests and then compared with FE model results. Forced vibration tests on the dam were performed with two exciter units on the dam crest for alternative conditions of in-phase and out-of-phase cases. Test records were processed using PSD, CSD and Coherence Spectra through MATLAB software. Consistent conformity between experimental and computational 8 middle modes of the Dam-Reservoir-Foundation system was achieved by the particular algorithm proposed in this research.

In this article at first the wavelet theory is described that if s advantages are informations about the location of frequencies content in the time domain, determining noises and denoising them from raw dataor process, knowing about distributaries of energy of signal at time-frequency space,... which can be used for fast computation and relatively exact analysis of structures. In following for a SDOF system of vibrationa relationship between input wavelet coefficient and output (response) wavelet coefficient is provided. So with input wavelet coefficient before exact analysis the response or excited modes of vibration of MDOF systems can be determinate and by facilities of wavelet transform, the response of system with denoising that cause lower memory occupation or how energy of process is distributed around specific scales, fast computation can be done. At the end, for demonstration of the true and accuracy of this method some examples are solved. It is nicely recommend that this method can be provided and adapted for MDOF system of vibration.

Seismic behavior of reinforced concrete braced frames is investigated in this paper. Study includes the modeling of some two Dimensional Reinforced Concrete braced frames using nonlinear static and dynamic analysis. The results of braced frame analysis such as stiffness, strength, ductility and energy dissipation are compared with those of Reinforced Concrete frames and Reinforced Concrete frames with shear wall. This comparison concludes that Reinforced concrete braced frames have better seismic performance.

In this paper, synthesis and formation of molybdenum disilicide from stoichiometric mixture molybdenum and silicon powders by mechanical alloying have been investigated. In two stages and with the same test conditions, mechanical alloying has been done on (Si) + Mo and (Mo) + Si powders. Experimental results demonstrate that for synthesis MoSi2 by mechanical activation, (Si) + Mo is more effective than (Mo) + Si. Since the silicon is more brittle than the molybdenum, thus silicon powder particles with mechanical activation is fractured quickly and contact area is increased. Finally molybdenum disilicideis formed with increasing contact area and preparing primary activation energy during mechanical alloying.

The concept of critical gate entry velocity was investigated in AZ91 magnesium alloy. The effect of in-gate velocity on the soundness and the mechanical properties of aluminum castings has been reported. Due to surface turbulence resulted by exceeding from the critical velocity and the entrainment of oxide film, mechanical properties and the performance of casting might be reduced significantly. Experimental work consisted of casting of plates, 10x140x200 mm of the AZ91 alloy in resin sand mold. The molten metal was introduced into the mold cavity at different gate velocities via changing the dimensions of a bottom gated filling system. Video recording was used to evaluate the possibility of the surface turbulence and the direct observation of the morphology of entrance of the melt jetted into the mold cavity at different velocities. Bend tests were carried out to investigate the effect of gate velocity on the mechanical properties of the castings in vertical and horizontal directions. Some results indicated that critical in-gate velocity for alloys is approximately 0.3m/s. Laminar fluid flow was observed at and below this velocity while at higher speed the morphology was changed into a mushroom shape and fountain shape of flow was noticed followed by about 50% decreased in the mechanical properties.

The specific rate of breakage is one of the most important factors in evaluation of grinding process especially in ball mill.In this article the effect of ball size and feed size on selection function were investigated in a batch grinding circuit on tow iron ore anomaly (B,C) from Sangan mine in north of Iran . Eight different monosize fractions were prepared between 2000 and 500 micron, using a Ö2 sieve series. The specific rates of breakage (Si) were determined from the size distributions at different grinding times, and the specific rates of breakage were compared for three different ball diameters.

In this paper, desilication experiments on calcined diasporic bauxite by thermochemical treatment are investigated. For this purpose, calcined samples at specific temperature were leached with caustic soda at 95°C. The experiments are conducted in two sections: optimizing calcination conditions and determination of leaching parameters. Calcinations experiments revealed that the optimum calcinations temperature and time are 1000°C and 60 minute respectively. By optimizing these parameters, 42.22% of bauxite silica content is extracted and module ratio (ratio of Al2O3 to SiO2) reaches to 2.94. According to leaching experiments the optimum leaching parameters is determined as: leaching time 120 minutes, caustic soda concentration 200 g/L, pulp dilution 4 and particle size below 210 mm. As a result, silica extraction percentage and module ratio increase to 50.92 and 3.5 respectively.

Shaking table is one of the most effective devices for gravity concentration which is used in coal washing for the particles sized from 0.15 to 9.5 mm. In this research, some parameters were determined such as longitudinal tilt, slide tilt and frequency which affect efficiency of shaking table. 16 one - parameter tests were carried out in order to determine the aforementioned parameters. Therefore, the optimum range of longitudinal tilt, slid tilt and frequency obtained were 0 to 0.5 degree, 3 to 4 degree and 240 to 260 cycle per minute respectively. Since there may exist interactive effects among these parameters, a three-parameter Hdamard experimental design was carried out on the optimum range of above parameters. Results of this experiment show that interactive effects exist between these parameters, and optimum rate of the longitudinal tilt, slide tilt and frequency are 0 degree, 3 degree and 260(rpm) respectively. Separation efficiency for these parameters obtained were 64.2%, 55.5% and 47.55%, respectively.

One of the less expensive methods to investigate the ore deposit weathering surface is to investigate the geochemical haloes exact positions. The following research is a try to apply the sufficient computer software too quantitatively, processing the litho-geochemical data from the available drill cores to find the development values of the maximum weathering from the Anjerd skarn, northwestern Ahar. By identifying the amount, magnitude and the location of complex and the multiple haloes, it is possible to find the weathering effects within this ore deposit. The upper and downer elemental haloes in the southwestern part of the deposit is very intense, which is corresponded to the low alteration effects, in other words it is possible to say that the alteration could not effect the ore main body and most part of the deposit is intact and preserved. In complex haloes investigation, it is showed that there is an intact ore body toward the northwestern, in addition to that of southwestern part of the studies area. It is also proved that there is no chance of ore formation within the deep part of the area, and the only economic ore formation could happen in the maximum depth of 80 meters. In general, it is concluded that the continuing the mineral exploration activities within the studied area could be more satisfying if it is in two locations of northwestern and the southwestern of the main studies area.

In many cases, analysis of mine ventilation networks by ordinary mathematics is impossible and we have to use numerical methods. Newton - Rephson method is one of them which is being used for solving the mathematical equations. Although this method is used for analysis of water distribution networks, but in mine ventilation networks has not been used. In this paper, using of this method for solving the DQ equations is discussed.