نشریه مکانیک مواد پیشرفته و هوشمند
سال سوم شماره 2 (پیاپی 8، تابستان 1402)

In conventional vehicles, about 40% of fuel energy is converted into useful power, and the rest is directed to the environment by cooling and exhaust systems, which, in addition to energy loss, are also one of the main sources of air pollution. At present, all over the world, food suppliers use online orders for their customers to move ready-made food from the place of production, such as restaurants, to their destination while maintaining its quality. However, along this route, due to the long distances that cause heat loss from the food container, it creates problems for food to cool or heat drinks in online orders. Therefore, using a thermosyphon in the exhaust gas path to recover waste heat is one of the methods that can be used in addition to solving the problem of existing pollution with heating applications and also for cooling applications of vehicle electricity as chamber cooling. In this research, a mobile combined cycle (heating-cooling chamber) was used to keep the chamber warm with the best filling percentage of 75% in all inlet capacities for 25 minutes to about 48 °C using a thermosyphon and cool the other chamber for 8 minutes. It was designed and built up to a temperature of about 5 °C with the help of thermoelectric cooling.

It is very important to improve the parameters of the electric motor in order to improve its performance. One of the ways to improve the performance of electric motors is to use permanent magnets in the structure of induction motors. These types of motors are known as line start motors. The use of permanent magnets eliminates ohmic losses and increases efficiency. Due to the fact that permanent magnetism plays the most important role in these motors, the smallest change in the magnetic properties of the used magnet will cause malfunction of the machine. One of the important phenomena that changes the properties of the core magnet is the phenomenon of demagnetization. Although this phenomenon has very destructive effects on engine performance, the design of electric motors is still done without considering this issue. In this article, a line start motor is designed. The numerical simulation results show that the performance and efficiency of the motor in the demagnetization mode are significantly reduced. Also, the increased current in demagnetized motors causes a further decrease in the magnet's magnetic properties. This effect is progressively repeated many times until the property of the applied permanent magnet is lost. Finally, an analytical model was presented for examining and designing electric motors, considering the effects of demagnetization. The results showed that the use of the analytical model of motor design considering the effects of demagnetization can be a suitable alternative to the use of conventional methods in the design of electric motors.

In order to facilitate the transportation of the wind turbine tower, the tower is made of several separate parts and they are flanged to each other and fixed by the welding process. An unwanted consequence in the welding process is the distortion caused by the uneven distribution of heat in the flange. This consequence appears as residual stress and permanent deformations in the flange. In this research, the distortion in the welding of the wind turbine tower flange is studied. Numerical and experimental results show that the amount of heat flux has the greatest effect on flange distortion. By writing a subroutine and using repetition and conditional loops, the path of the welding nozzle is defined for the program and the amount of distortion caused by the heat distribution is predicted with appropriate accuracy. The comparison of numerical and experimental results shows that the difference of the displacement results depends on the cross-sectional area of the flange and its angular position. In the outer region of the flange, this difference is close to zero percent in all positions. In the middle areas of the cross-section in the angular position of 60 degrees, this difference is 33%, which has the lowest percentage difference compared to the positions of zero, 30 and 90 degrees. In the inner areas of the flange at an angular position of 30 degrees, the displacement difference is 14%, which is the least difference compared to other positions.

The presented paper investigates the flutter phenomenon in a rectangular-shaped plate in supersonic air flow. First, the phenomenon of flutter and its identification method based on the analysis of eigenvalues are presented. Then, using the assumptions of Kirchhoff plate, the plate motion equation is derived and coupled with the first-order piston aerodynamic model. Next, the coupled structure-fluid equation is solved in matrix form using the differential quadrature method (DQM). Using the DQM numerical method in matrix form provides advantages such as high accuracy for solving the flutter problem. The obtained results show that the first phenomenon of flutter in an aluminum plate with a length and width of 1 meter and a thickness of 5 mm with clamped-free-clamped-free boundary conditions occurs in dimensionless dynamic pressure 617 (equivalent to Mach 3.395). The presented formulation can be used as a benchmark for solving and calculating the flutter speed of various objects in the supersonic air flow.

In recent years, ring rolling process is used to produce seamless rims in many industries, including the aviation and railway industries. The reason for this is the advantages of this process, such as saving money and materials, high quality and high efficiency. In this research, the shaping of the front and rear spools of an airplane engine compressor has been investigated using the ring rolling process. Due to the complexity of the internal and external surface shapes of these spools, it is difficult to simulate the ring rolling process for them. For the performed simulation, the stress applied to the main roller has been checked with the assumption of the shape of the rollers. Also, the forces acting on the main roller in the case where the rollers are assumed to be malleable have been extracted and compared with the previous results where all the rollers are rigid. In both spools, there are complex forms designed on the surface of the roller. If the concentration of stress created at the sharp points during elementing is ignored, the stresses created on other parts of the mold are around 400 MPa. Therefore, H13 steel can be used for the front and back spools to make all molds. But it is suggested that the surface of the shell should be as hard as possible and after making molds and using them for the mass production of shells, these surfaces should be constantly reviewed.

Composite shells are widely used in various industries due to their low weight and high strength. Designing these structures involves various engineering analyses, and one of the most important studies is the investigation of the buckling of shells under axial load. The aim of this research is to investigate the vibrational correlation method on composite cylinders with delamination defects. Delamination defects can occur in structures under different conditions and have a significant impact on the strength of the cylinder. Therefore, in this study, different dimensions and quantities of delamination defects in various specimens were examined using the vibrational correlation method. Carbon fibers of type T300 were used as the reinforcement material, and the epoxy resin LY556 was used as the matrix. The hardener and accelerator combined with the resin in this research are HY917 and DY70, respectively. The layer stacking in the specimens was done with angles [55 90 90 55] using the filament winding method, and artificial delamination defects were created between layers 2 and 3 using Teflon sheets. The manufactured specimens were subjected to modal testing under various compressive forces, and then the critical buckling load of the specimens was obtained using the modal testing method. Using numerical modeling software, critical buckling loads and natural frequencies were calculated for various axial compressive loads through linear and nonlinear analysis. These numerical results were compared with experimental results. The vibrational correlation method accurately predicted the critical buckling load in defect-free specimens with a 3% error, but its accuracy was significantly

In this research, several samples of thick sheet metal from the fracture area and its surroundings related to a crane have been examined and studied in order to investigate the causes of destruction in this research. The studied sample is related to a German-made rail crane that was built in 1974. In order to investigate the causes of destruction, first the fracture surface and the external surface of the sample were studied by a stereo microscope. Then, the chemical analysis of the sample was determined by the emission spectroscopy method. In order to investigate the microstructure, metallographic samples were prepared from a cross section and studied by an optical microscope. To determine the mechanical properties, hardness and tensile tests were performed at ambient temperature. To complete the studies, the fracture surface was examined by scanning electron microscope. Based on the studies conducted and the results obtained from the experiments, the main cause of failure is fatigue corrosion. Relatively deep corrosion pits on the surface along with surface cracks in the uncovered areas indicate the occurrence of corrosion, which has led to failure by considering the service time, the presence of working stresses (mainly cyclical) and overload conditions at certain times.