مجله مهندسی ساخت و تولید ایران
سال چهارم شماره 2 (پاییز و زمستان 1396)

Piezoelectric materials are materials that convert electric energy into mechanical energy (acoustic), and vice versa with mechanical pressure on them, electrical energy is produced. The use of lead-free piezoelectric materials in the bone is developing due to its piezoelectric properties. The aim of this study was to investigate the piezoelectric effect of barium titanate. Barium titanate is a bioactive material that is suitable for use in bone tissue engineering. In barium ceramics, non-polar titanate, ferroelectric regions are randomly oriented, and thus the piezoelectric properties are minimal. Therefore, there is a need for polarization to increase piezoelectric properties. For this purpose, this study was carried out by polarization with different voltage and time on two groups of implantation and porous scaffolds. The implants were made with different dimensions, then polished with different voltages and different times, and finally, their piezoelectric properties were investigated by piezoelectric devices. Also, three-dimensional scaffolds with a porosity of 80% were made using foam molding method. The scaffolds were then polarized in the oil at a different voltage and time, and finally, their piezoelectric properties were investigated by piezoelectric force. And then a biological test was performed on them. Finally, it was concluded that both implants and porous scaffolds with polygonation can find the proper properties for use in bone tissue engineering. It was also concluded that the higher the diameter of the implants, the lower the height and the greater the piezoelectric coefficient. Cell test results also confirmed the effect of piezoelectric properties on bone growth.

Due to its complex dynamics, turning process has always been of interest ýto ýmachining researchers and much effort has been made to determine the ýforces. The aim ýof this paper is to define the amount of ýdifference between ýAltintas formula, dynamometer value, and the value which ýis obtained by ýproviding a new method based. Practical tests are done to verify the results. ýThe tests are ýperformed for boring state with different parameters and the ýforce signal is determined using a ýdynamometer andthe new method in which ýthe acceleration of one point of the ýtool is used. Using the results of these two ýsignals, the parameters needed to ýcalculate the force components in Altintas ýapproach and the new method are ýderived. The results ýshow that the tool tip ýforce, resulting from the new method which considered ýthe effects of ýdisplacement and acceleration tool, obtains the greatest force ýamplitude. The ýforce at the end of the tool which is derived by dynamometer ýhas lower and ýthe force resulting from Altintas approach has the lowest amplitude, in which ýthe cutting force is ýonly considered as a factor of chip dimensions. Therefore, ýbecause of their ýimportant differences, these forces should not be used ýinterchangeably.ý

Replacing missed teeth with artificial metallic implants is a pervasive treatment nowadays. With the advent of research on biomedical and mechanical properties of oral and dental issues, implants have seen a great deal of improvement in terms of dimensions, design of body and materials, methods of production and surface type. Performance of implants in the teeth is affected by oral conditions and phenomena such as corrosion and fatigue along the life time. In this study, the corrosion phenomenon has been experimentally studied with similar oral conditions in a variety of dental implants, focusing on construction methods, materials, and surface conditions. The combination of various fabrication methods, such as machining and 3D printing (selective laser melting) for steel and titanium specimens with a variety of surface conditions, including samples with different threads and samples with biocompatible coatings is applied in the survey. Results show that in general, by increasing the complexity of the implant surface, which includes the method of selective laser melting or creating higher ripeness at the surface by adding a second thread, machining variant depth thread or applying appropriate coating on the surface, hydroxyapatite coating, the resistance to corrosion of the implants will be improved. Also the results show that titanium alloys have a higher corrosion resistance than stainless steels. In addition, applying modern manufacturing methods in the production of implants, particularly three-dimensional printing techniques such as selective laser melting, used in this survey, improves the implant's mechanically performance specially Corrosion resistance rather than the conventional machining method.

Currently, improving microstructure of new casted turbine blades by applying uniform pressure at high temperatures is considered as one of the common steps in their production. The operation performed on the serviced-exposed blades can be effective in extending the blade lifetime through the closing and welding of creeping cavities and micro cracks. Due to the lack of adequate existing information, the present study attempts to create the same conditions by studying the experimental process. For this purpose,at first, a special measuring fixture was designed and fabricated. Then, a disc containing 75 first-row blades of the Ruston power turbine was measured on longitudinal direction, and six of them were selected with the highest longitudinal creep. In the next step, the pressure and high temperature tank as well as the furnace needed for the tests were prepared and adjusted. The samples were then subjected to a pressure of 150 bar and a temperature of 380 ° C for eight hours. Metallographic studies showed that the percentage of γ^' phase in various areas of airfoil increased by about 25%, and the hardness in these areas was increased by a maximum of 7%, which, according to the operating conditions, indicated that the mechanisms for improving the microstructure were active. Using the experimental data and the Monkman-Grant relationships and the Larson-Miller parameter, it is expected that the creep life of this blades will increase by about eight thousand hours.

There are many common defects produced during the drilling of composite sandwich panels such as delamination, uncut fiber and matrix cracking factors. In this work, we employed the Epoxy / Kevlar with Balsa wood and Polyvinyl Chloride (PVC) foam core in sandwich panel under different drilling factors i.e., cutting speed, feed rate and tool diameter and examined in three levels. The major aim of this study is to find the best conditions for producing the machining holes in sandwich panels with considering the delamination and uncut fiber factor. For better analysis, we used the digital imaging techniques as a reliable way to measure and determine the level of damages. The results showed that the machine spindle speed, feed rate and tool diameters have so effects on delamination and uncut fiber factors. The obtained results are given to assess the applicability of the mentioned sandwich panels in industrial specialty in aerospace and military purposes.

In this paper, thermo-mechanical behavior of the welding process was analyzed to determine the effect of wall thickness on the residual stress magnitude and distribution in the stainless steel pipes. In order to verify the model, experimental data for the steel pipes, obtained by Deng with deep hole drilling method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the residual stress of similar weld joints. The present finite element model was developed in a butt-welded pipe to consider the effect of pipe wall-thickness. It was observed that by increasing the preheating temperature in the repair welded pipes, tensile axial residual stresses on the inner surface and compressive axial residual stresses on the outer surface of the stainless steel pipes decreased about 35 and 25 percent, but the compressive axial residual stresses on the inner surface and tensile stresses on the outer surface have small variation. Moreover, by increasing the wall thickness of pipe compressive hoop residual stresses on the inner surface on the stainless steel increased, but only a small variation was observed on the tensile hoop residual stresses. In general, there is no significant effect on the magnitude and distribution of hoop residual stresses on the inner surface of the stainless steel pipe. Also, high wall thickness will have wider distribution of axial residual stresses.