نشریه مهندسی مکانیک مدرس
سال بیست و سوم شماره 4 (فروردین 1402)

Regenerative pumps are pumps with a very low specific speed. The main characteristic of regenerative pumps is the ability to produce high heads at low flow rates.  In this article, numerical and experimental methods have been used to analyze and improve the performance of regenerative pumps and also to investigate the effect of leakage flow around the impeller. In order to validate, an experimental test circuit of regenerative pumps has been designed and built. The comparison of the numerical and experimental results have a good agreement, which indicates the high accuracy of the numerical simulation. Based on the results of the study, we conclude that increasing the geometric thickness of the leak leads to an increase in mixing the high-pressure fluid of the outlet nozzle with the low-pressure fluid of the inlet area, leading to a decrease in the generating head generated by the regenerative pump. The performance parameter of efficiency will also decrease significantly by increasing the geometric thickness of the leakage to 0.4 mm compared to the original geometry with a leakage of 0.26 mm. On the other hand, reducing the leakage thickness to 0.2 mm will lead to the improvement of the functional parameters of the head and the efficiency of the reproducing pump. Also, the ideal geometry without leakage has been introduced and calculated for the maximum and theoretical limit of head and efficiency parameters.

Thick-walled cylindrical vessels are specially used in oil, chemical, nuclear and military industries in order to withstand internal pressure. The presence of the compressive residual stress in the walls increases the bursting pressure and fatigue life. Autofrettage processes and radial interference in multilayer cylinders are among the conventional methods of creating residual stresses in the pressure vessels. In order to achieve higher strength and fatigue life, the combination of these processes is also considered. J integral method is a suitable criterion for evaluating the crack parameters in elastic and elastoplastic strain fields. In this research, distribution of the J integral along the semi-elliptical crack front on the inner surface of the interferenced two-layered cylinder with closed end has been studied. Inner layer was autofrettaged. Burst pressure was determined based on the fracture toughness criterion (JΙC). Also, the effects of the autofrettage percent, radial interference; depth, angle and aspect ratio of the crack on the J integral and burst pressure variations have been investigated. The inner and outer layers of the cylinder were made of 7075-T6 aluminum alloy. The periodic nonlinear hardening behavior of this alloy has been predicted using Chabooche model. The validity of the results and their accuracy were examined

Pneumatic Soft bending actuators as safe and highly adaptable robots are being considered by researchers, such that they become an ideal choice for making devices that interact more with humans. These advantages come along with several disadvantages. Their great adaptability is provided by their high degrees of freedom, and consequently, it makes the modeling a significant challenge for researchers. In this paper, the modeling of a soft fiber-reinforced bending actuator that is in contact with the environment has been conducted by utilizing the finite rigid element method. This method provides a context within which the modeling theories of traditional rigid robots, such as the Denavit-Hartenberg method, become usable for a soft continuum actuator. Therefore, in the following, resorting to this theory, the static and dynamic behavior of a soft actuator under the effect of the external load has been investigated and compared with the empirical results derived from a fabricated actuator. The results show a minimum accuracy of 9 percent, although being as simple as can be used for other purposes like implementing control systems based on that.

Today, the application of materials such as glass has been widely developed in the manufacture of micronutrients, electronics and medical equipment because of its high hardness, chemical resistance and high abrasion. But due to high hardness and low toughness, mechanical machining can not be applied. The Electrochemical discharge method is a new machining method that is capable of machining hard and non-conductive electrical materials such as glass. In the process of electrochemical discharge drilling, the dimensional accuracy of the hole and especially its inlet area is important. but almost, the inlet of the hole has a high slope, which leads to excessive hole overcut and tapering of the hole side wall. In this study, to remove the high slope entrance area, a thin intermediate part was used which will be separated from the main workpiece after the drilling process. The results showed that mentioned method reduced the entrance overcut of the hole by 50 to 76% depending on the diameter of the tool. Also, the hardness measuring of points on the hole inlet showed that using the intermediate part led to the smaller heat-affected zone (HAZ) around the hole entrance.

Thin-walled tube bending is one of the important processes for manufacturing parts in the automotive and aerospace industries. This paper investigates the effect of heat treatment on the bendability of thin-walled tubes made of AA6063 alloy. With the hydro rotary draw bending process, the cross-section ovality of the as-received, annealed, and artificial aged tubes has been examined at different fluid pressures. In the experiments, the tube diameter to tube thickness ratio was 13.88. Also, the critical bending ratio was 1.6, and the bending angle was 90 degrees. By examining the results, it has been found that heat treatment and fluid pressure had an important effect on the quality of the bent tubes. By increasing the fluid pressure to 3.6 MPa, critical cross-section ovality has decreased in all specimens. The maximum decrease of cross-section ovality is obtained in the annealed sample by 49%. Also, in the artificially aged specimens, the critical cross-section ovality decreases by about 45%. It has also been observed that at a pressure of 3.6 MPa, the critical cross-section ovality of the annealed sample has improved by 19% compared to the artificially aged specimens.

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.