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Determination of soil engineering properties such as shear strength is essential to analysis many geotechnical problems. Therefore, determination of the reliable values for this parameter is very important. For this purpose, direct shear test as one of the oldest test to examine the shear strength of soils, is conducted on soil samples. There are too many factors which could affect results of direct shear test. Laboratory tests are expensive, difficult and time consuming, hence using numerical method to simulate experimental test and study effective factors could be useful. In this paper direct shear test was numerically modeled using CA2 hybrid finite element-discrete element method code. CA2 solves explicitly equations of motion together with macro or micro-constitutive equations. In this study, shear box is modeled using finite element grids and a discrete element model is implemented for simulation of soil specimen within the box. Appropriate boundary conditions are assigned to the box, normal stress is applied to the specimen using finite element grid and shear velocity was finally applied to the model. Shear force is applied to the model by a constant velocity 4.5×10-9 meter/cycle. It should be noted that, shear velocity is applied to the upper part of shear box, and applied velocity is considered small enough to confirm that there is a quasi-static condition in numerical solution. In this study using numerical simulation, the effects of box dimension, genesis pressure, normal stress, shear velocity and box wall friction on shear strength of the soil specimen are investigated. Study of box dimension effect, shows that peak effective internal friction angle in small direct shear box and large direct shear box differs about 6°, and cohesion decreases by increasing box dimension but for box dimensions bigger than 20cm, changes in box dimension has no significant effect on resulted soil cohesions. Investigation of influence of genesis pressure shows that, incrementing genesis pressure, cohesion increases too, that can be attributed to the SOCPI model provided in CA2. In SOCPI model by increasing genesis pressure the overlap between cylinders increases. In SOCPI model by increasing overlap the cohesion increases but peak friction angel doesn’t change too much. Normal stress analysis shows that, increasing normal stress, interlocking between soil particle increases and more interlocking causes increasing cohesion of the soil model. Shear velocity is another parameter which is studied in this research. Results show that by increasing shear velocity, soil shear strength increases. It should be mentioned that shear velocity should be considered as small enough to result in a quasi-static solution; for velocity smaller than that model run time increases ineffectively. In this research, friction of shear box wall as one of the important parameters in study of soil shear strength is also investigated. When there is friction between box wall and soil particles, shear strength can be underestimated for contractant soils or overestimated for dilatant soils. In this paper, it is shown that if soil has no significant volume changes, peak shear strength is not affected by friction between soil particle and box wall.

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In present study, the stress and strain distributions due to the radiant gradient in some radiant tube burners have been investigated. In the design of the burner, several outlet valves are mounted on the wall of the burner tube and the combustion-produced fluid is discharged by the outlets into the furnace. For this purpose, three cylindrical radiant tubes with the same length, diameter, thickness and material and difference in design of fluid outlets are modeled. To simulate the mechanical behavior of the pipes, after the geometric modeling and considering the pipe material and boundary conditions, ANSYS commercial software has been used. The boundary conditions for numerical solution are extracted from the results of the experimental tests. Due to the average fluid velocity within the radial tube, the fluid flow falls into the turbulent range. In order to obtain the stress-strain diagram of the tested alloy, the Ramberg-Osgood equation is used. Due to the solution of the fluid-solid interaction by ANSYS, the best design is concluded through the Von-Mises stress minimum values. Also, by removing the thermal load from the next load step, the residual stresses generated in the samples are calculated. To illustrate the accuracy of the solution, some specimens of the burner have been made and evaluated to verify the numerical solution.

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Nowadays using 3D printing for prototyping is well known in industrial applications and there are efforts to make functional parts with this technology to reach low volume production markets. By using pellets rather than filaments, the limitations caused by lack of variety of materials can be conquered. Also there will be no need to make a massive part as several divided parts and then glue them together.
In this article pellets of ABS, that are well known and functional in industry, are analysed for an extruder to investigate the ability of pellet material extruding. Characteristic specifications of extruder such as operating pressure, screw rotational speed and required torque for rotating the screw are achieved for they are important factors to find out the mechanism for experimental tests and selecting suitable operating parts such as motor and gearbox. At the end, the experimental tests on designed system are done and the result approved the trends of theoretical data.
 

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