نشریه مهندسی مکانیک مدرس
سال بیست و یکم شماره 3 (اسفند 1399)

Today, a variety of implants with different applications are used to replace or support a damaged biological structure, the most common of which are dental and orthopedic implants. Due to the widespread use of stainless steel 316 L in the manufacture of implants and the occurrence of cracks and residual stresses during the process of electrical discharge machining for the production of these products, the use of effective and economical polishing methods such as burnishing in It is effective in increasing the surface properties and compatibility of these products with living tissue. In this study, after performing the electrical discharge machining process on the surface of the sample and making the ball burnishing, the burnishing operations were performed by changing the input parameters and in accordance with the experiments designed using the mini tab software. Thus, the effect of variable burnishing force, feed speed and number of tool passes on surface roughness properties, micro-hardness and corrosion resistance of the final surface of the work piece were investigated. During the optimization of the response surface methodology, the optimal value for surface roughness, micro-hardness and surface corrosion rate of the samples were obtained, respectively, 0.108 μm, 435.34 Vickers and 2.18*105 respectively. Compared to the control sample, the surface roughness of the samples decreased by about 97% and the micro-hardness and corrosion resistance of the samples increased by about 2 and 11 times, respectively.

One of the major problems in the world is the supply of energy. Biodiesel is one of the alternative fuels and renewable energy sources. The use of B5 biodiesel in diesel fuel mixtures is common and most countries have planned to use B20 biodiesel. The use of natural gas in diesel engines and the study of the possibility of using it in high quantities is another new solution, which can reduce dependence on diesel fuel. In this study, biodiesel was produced from waste oil by transesterification process and used in two levels of 5 and 20% in diesel composition. Then natural gas was used in three levels of 60, 70, and 80% (% G / T) in the diesel engine. Engine tests were performed at full-load at 1500 rpm. In general, the test results showed that in conditions where biodiesel B20 was used in the composition of diesel fuel and gaseous fuel was used in the amount of 80% in a diesel engine, suitable conditions in terms of reducing emissions, increasing energy efficiency, and reducing economic costs were obtained; Under these conditions, compared to a conventional diesel engine, brake power, and energy efficiency increased by 8.86 and 29.06%, respectively. Also, brake specific fuel consumption, CO and CO2 were reduced by 26.5, 57.58, and 4.54%, respectively. Although the amount of NOx increased slightly, but, decreased the economic cost compared to diesel 26.47% $/kwh, so the results were valuable.

In the present study, the usability of high-density polyethylene (HDPE) based composites in medical applications under impact loads was investigated. Due to the importance of biocompatibility of composites in the medical applications and body environment, zinc oxide nanoparticles (ZnO) were selected as reinforcements. ZnO nanoparticles are generally safe and have superior antibacterial properties. A finite element simulation process with a new approach were used to study the impact properties of the composites in the standard Charpy impact test; moreover, in the experimental procedure, a new method was introduced for the production of HDPE/ZnO composites without use of the compatibilizers. Fourier-transform infrared spectroscopy (FTIR) test was used to check the diffusion of particles in composites. Field emission scanning electron microscopy (FESEM) was utilized to examine the presence of particles in composites. The results of the simulation showed that the HDPE/1%ZnO composites have the best impact resistance in comparison to other composites. Experimental results also showed that HDPE/1%ZnO composites have the best performance in terms of impact strength with an error of about 11% compared to simulation results and are economical. Moreover, the results of antibacterial test of HDPE/1%ZnO composites confirm the excellent performance of this composites against gram-positive and negative strains.

Due to the increasing expansion of products made of plastic materials, high percentage of plastic waste enters the waste and waste annually, and the recycling of these plastic wastes is usually accompanied by decrease in their mechanical properties. One of the simplest and the most affordable ways to overcome the decline in mechanical properties during use recycled polymer, is achieving optimal combination virgin polymer and recycled polymer via mixing together. In order to produce products with both high quality and optimal mechanical properties will be desirable. Accordingly is beneficial for both environment and economic point of view, reducing use of virgin polymer.  In this study, in order to investigate the effect of weight percentage of recycled polyamide 6.6 with virgin polyamide 6.6 on the mechanical properties by injection molding proses, mix recycled polyamide 6.6 and virgin polyamide 6.6 with different weight percentages is prepared and then is injected. The results of mechanical tests on injected samples showed that adding more than 50% by weight of recycled polyamide 6.6 to virgin polymeric materials increased melt flow index, glass transition temperature and crystal temperature. While, the mechanical properties of samples decreased with increasing weight percentage of recycled polyamide in the composition. These changes were less for some properties such as tensile and flexural strength and more for impact resistance. Tensile and flexural strength and impact resistance in samples with 50% by weight of recycled polyamide in the composition, respectively, decreased by about 6%, 9% and 34% compared to the new polyamide sample.

The aim of this paper is to analyze the strain components in the direct extrusion process to predict the curvature of the exit product. For this purpose, Riemann mapping theory is used to model the deformation zone and create a one-to-one correspondence between the input and output cross sections of the die. With the help of the Bezier curves, flow lines are created between these points and then an upper bound solution is obtained for the velocity field. The process pressure and the distribution of the strain components are determined for the square, hexagonal, and rectangular sections using the obtained velocity field. A theoretical method based on the elastic-plastic bending of beams is presented for calculating the curvature of the exit product for the eccentric dies. In this theoretical method, the distribution of stress components and the bending moments is calculated using the specified strain components. In fact, the amount of bending moments indicates the curvature of the exit product. Finally, the presented theoretical model is validated through comparison with the results of the finite element simulation and the previous studies. The results show that Riemann conformal mapping theory and upper bound method can be used to determine the distribution of strain components and predict the curvature of the output product, in addition to estimate the process pressure.

Arak is ranked 71st in the worldchr air is more polluted than the Iranian capital in terms of pollutants. The influx of large amounts of pollution into the city shows that a high percentage of pollution is concentrated in a small town, and this volume of pollution is very dangerous for both humans and the environment. In order to reduce air pollution in the city, the Iranian government in 2007 approved a plan called the comprehensive plan to reduce air pollution in Arak. In this comprehensive plan, the construction of a highway called Amirkabir (58 meters) has been approved, which connects the east and west of Arak. In this article, numerically and experimentally, the effect of constructing this highway on the reduction of air pollution in Arak city has been investigated. In the results section, the details of changes in air pollution in Arak city before and after the construction of this highway have been compared. The results show that a 2.75 percent decrease is observed for Nox pollutants, 4 percent decrease is observed for Co, and a change is obtained for So2. As a result, the implementation of this project at a very high cost will not have a significant impact on improving air pollution in the city of Arak.