نشریه مهندسی مکانیک مدرس
سال بیست و سوم شماره 2 (بهمن 1401)

In forging of bimetallic components, products with a high strength to weight ratio can be obtained. The purpose of this research is to forge a bimetallic component made from aluminum and brass alloys as the inner and outer parts, respectively. The forging temperature for the brass and aluminum alloys is considered in the hot work range as 700 °C and 450 °C, respectively. First, the forging of a single component is investigated numerically and experimentally. After validating the finite element model, bimetallic components are forged in single stage. The effect of brass ring thickness and height difference between aluminum core and brass ring is studied on the success of the single-stage hot forging process. The results show that the thickness and height of the brass ring do not have a significant effect on the success of the process in terms of complete covering of the core by the ring. In the following, to solve this problem, non-simple geometries are designed for the core and ring as a preform, then forging of the second stage are numerically investigated. The results show that in order to produce a bimetallic component with a complete covering of the aluminum core by a brass ring, a two-stage forging is needed using a suitable non-simple preform. Finally, the preform approved by the FEM is experimentally produced and hot forging is performed on it. The experimental results confirm the numerical results. SEM images show that an appropriate metallurgical bonding is created at the interface of two metals.

The critical Crack Tip Opening Angle ( ) is considered as a convenient parameter to characterize the crack arrest toughness of natural gas pipeline. Load-displacement curve is a comprehensive reflection of geometry, mechanical property and fracture behavior of a loaded specimen, so it would be highly advantageous to deduce   from load-displacement curve directly. From force-displacement curves, maximum force of 209kN and 207kN were obtained for experimental and numerical data, respectively. In this article, a combination of load-displacement and deformation of the drop weight tear test specimen was used to calculate the critical crack tip opening angle. For this purpose, the simplified single-specimen test method was used. The   is dependent on the slope of the steady-state crack growth region and the plastic rotation factor. Firstly, based on the fact that load decreases linearly with the increment of displacement during steady-state crack growth, the slope of the experimental load-displacement curve of API X65 steel in the steady-state crack growth region was obtained as 21.583. Secondly, by modeling the drop weight tear test in Abaqus software and using two methods of mises stress and neutral axis, the plastic rotation factor was obtained as 0.5688 and 0.5651, respectively. Finally, these parameters were used and the critical crack tip opening angle was determined as 12.00 and 12.08 degrees.

Wingsuit flying is one of the most popular flight disciplines in recent decades. In the aviation profession, efficiency and safety are paramount concerns for costume designers. An article in this issue examines how waveform changes to the wing surfaces of a wingsuit model improves aerodynamic performance. In order to increase performance, vortices are produced inside the boundary layer that improve the exchange of motion. In this experimental and numerical study, we investigate the formation and evolution of vortices in the Reynolds number range of 106 and provide insights into flow patterns on surfaces with geometric changes. A detailed study of flow structure can be obtained from experimental and numerical evaluations. According to the results, there are significant vortex generators near the backpack due to high pressure. Immediately after the creation of these vortices, the flow is drawn and spread on the surface of the wing in three dimensions. As a result of the angle of attack, the wing surface separates prematurely. Based on the lift and drag coefficients, the study model showed the best performance in flight at an angle of attack of 10 degrees for this flow regime.

The present study examined the pool boiling process in a specific geometry by designing and constructing a laboratory complex. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on a ring wire in deionized water at different temperatures. According to the results, increasing the number of rings and fluid temperature decreased the critical heat flux. In the case of a ring wire with a constant number of rings, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the number of rings, a fluid with a constant temperature and applying critical heat flux values. In a ring wire with a constant number of rings, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient decreased at critical heat flux values. The diameters of the produced bubbles were enhanced by increasing heat flux and they separated from the rings when combined. At the beginning of the reddening of the ring wire, a critical heat flux occurred, and considering 110% of the time required for the critical heat flux, the images of the state of the ring wire after the critical heat flux are presented.

These days, societies' need for energy increased due to the expansion of societies, industries, and technology. The production of electricity from renewable energy sources such as solar energy, which does not harm the environment and has little pollution, has attracted the attention of many researchers and engineers. This article will present a new plan for the dual polar axis solar tracker, its design and construction in laboratory dimensions, and the experimental evaluation of its performance using the open-loop control method. For this purpose, after examining the advantages and disadvantages of the previous designs, a new and different conceptual design for the tracker is proposed. Among the features of the proposed tracker, we can point out the ability to combine, install and operate quickly and easily, the self-locking feature, and the ability to rotate 360 ​​degrees around both axes. This tracker has no restrictions for use in different geographical areas, including areas near the North or South Pole and in the early and late hours of the day when the direction of the sun's radiation is strongly inclined. In the following, the detailed design of the proposed detector and the presentation of the open-loop control method will be discussed. Finally, by conducting experimental tests, the production power of the proposed detector is evaluated in comparison with a fixed solar panel. Based on the results, the electricity energy produced from the proposed solar tracker is 49% more than the fixed solar panel.

During root canal treatment, whole or a part of the tooth crown may be lost. Post and core is a method of repairing a damaged crown, in which a pinjet dipped in acrylic resin is used to mold the tooth canal and make a cast post and core. The main goal of this research is to produce an inexpensive pinjet with required strength and proper adhesion to acrylic resin. Therefore, to determine a right material for pinjet, lap shear and tensile tests were performed on eight polymer materials to check the adhesion of pinjet to acrylic resin and its yield strength, respectively. To produce some pinjets, a plastic injection mold was built and Moldflow Insight software was used to determine the process parameters of the injection molding. The results showed that HIPS 7240 with the lowest price among the examined materials and sufficient adhesion to acrylic resin is a suitable material for the pinjet. Also, this material with a yield strength of 10.91 MPa had an appropriate strength to prevent plastic deformation during the post and core molding process. While the injection time, melt temperature, and mold temperature were considered to 1 s, 230 ˚C, and 25 ˚C, respectively in both simulation and experimental methods, the injection pressure was 19 and 18 MPa and the injection speed was obtained 0.3 and 0.27 cm/s respectively in the simulation and experiments. Producing a perfect pinjet shows the ability and accuracy of the simulation in proposing the process parameters of plastic injection molding.