نشریه مهندسی مکانیک ایران
سال بیست و سوم شماره 2 (پیاپی 63، تابستان 1400)

In this paper, a new velocity field and the upper bound solution of rod drawing process througharbitrarily curved dies are presented. In analysis, the inlet and outlet shear boundaries ofdeformation zone have been assumed as flexible exponential curves. By using the continuity ofmaterial flow and the geometry of the die, mathematical equation of flow curve for each particlein deformation zone, is defined. By minimizing the required total power with respect to theshapes of the inlet and outlet shear boundaries, the drawing force has been determined.The rod drawing process is also simulated by using the finite element code, DEFORM. Theanalytical results have been compared with finite element data and the theoretical resultsobtained from a classic solution to illustrate the validity of the proposed upper bound solution.These comparisons show a good agreement. It was found that the proposed approach can resultin lower upper bound predictions while comparing with the results of previous work.

In the present study Charpy impact tests on a steel plate of API X65 (made from a pipe with adiameter of 1219 and a thickness of 14.3 mm) with full size (10 × 10 × 55 mm) with differentnotch depth (in the range of 1.25 to 3 mm) were conducted and the fracture energy wasmeasured. For this purpose, 24 specimens were made in triple series with 8 different notchdepths, and then the failure energy was obtained by Charpy impact tests. Also, computersimulation of the experiment with a three-dimensional model was performed based onGurson's modified damage law in Abaqus software. The experimental results showed that therelationship between the fracture energy (E) and the depth of the Charpy samples (a) for thetested steel is E = 499.65e-0.3501a. Using this relationship, the Charpy energy can bedetermined for this steel for any notch depth.

One of the most common defects in rotary equipments is cracks. Creation and growth ofcracks can cause irreparable damages as well as occurrence of unwanted vibration in rotatingequipments. On the other hand, increasing the damping of the system is one of the mostpractical solutions to control vibrations in rotating equipment. One of the most importantmethods to increase the damping is the use of squeeze film dampers. Despite the highefficiency of these elements in controlling the amplitude and damping of system vibrations,their nonlinear behavior has created many limitations in the use of this equipment.In this paper, the bifurcation analysis of a flexible rotor with a floating-ring squeeze filmdamper with centralizing spring and considering the occurrence of cavitation in the damper oilfilm and transverse cracks in the shaft is been investigated.

This manuscript discusses the mathematical modeling of a serial manipulator connetcted byrotary joints and fixed on a non-holonomic wheeled moving base. The equations of motion ofthe system are obtained in a closed form using the Gibbs-Appell formulation. Then, newkinematics and dynamics based multivariable controllers are presented by using the predictivecontrol approach. The control laws are derived by minimizing a quadratic cost function for thepredicted tracking errors of the mentioned system. Finally, the performance of the suggestedcontroller is presented by simulating a mobile manipulator in simultaneous trajectory trackingof the mobile base and end-effector.

The basic idea of this study is based on the relationship between the vibrational andmechanical properties of matter and its structural changes due to operation at hightemperatures. In this regard, samples of DIN X12CrNi2525 steel were aged at three differentworking temperatures for a full three days and nights, which led to the formation ofprecipitation and increased sigma phase. By comparing the results of experimental tests, wesee a very strong relationship between the properties of matter. By comparing the results ofexperimental tests, we see as the temperature of aging rises, the natural frequency of the firstfive modes and the damping coefficients increase. Also, the tensile modulus and the hardnessof the Vickers increase, as the temperature of aging rises. This study examines the feasibilityof developing a new and non-destructive method for estimating residual life using dampingcoefficients in the conditions of super-heating of power plant parts.

As the forces and moments for controlling the vehicle are generated between the tire and road, Therefore the tire model is very important in the vehicle dynamic. The Pacejka’s Magic Formula (MF) has become the most popular model. This model for describing the tire properties needs a set of parameters. In this paper the identifying of tire model coefficients discussed. Self-organizing maps (SOMs) was used for determining the parameters on the different road condition form high dry surface to low wet surface. The tests were taken with a vehicle that was used to conduct the real test at different road conditions. It was designed by Malaga mechanical research group. The effect of surface condition on the parameter of model discussed. A good Slip-Force ratio with the data that was not used in the network training was produced by the neural network so this method is feasible and easily obtain the parameter of each experiment on different experimental tests.

In this study, some parameters affecting the buckling load of stiffened cylindrical shells areinvestigated. These parameters include the type of connection stiffeners to the shell (weldingor glue and rivet), the number, thickness and shape of the cross-sectional area of the longitudinaland circumferential stiffeners, the shell thickness, the shape and the imperfection ratio and sizeof the cutout created in the shell. For this purpose, both analytical and numerical methods havebeen used. In the analytical method, the energy method is used and in the numerical method,Abacus software is used. In this study, in addition to previous works, on how to attach stiffenersto the shell, the effect of imperfection ratio of elliptic and rectangular cutout and also the effectof some parameters related to longitudinal and circumferential stiffeners such as the effect ofcross section shape and their number on the buckling load have been investigated separately.

Currently, with the advancement and development of the additive manufacturing technology(AM), many studies are conducted to evaluate the behavior and mechanical properties of latticestructures. Due to their ability to control mechanical properties, these structures have beenconsidered by researchers. In this paper, the properties and mechanical behavior of the kelvinlattice structure were investigated experimentally and numerically. The intended structure is316L stainless steel and is fabricated using the selective laser melting (SLM) method. The buildquality and mechanical properties of the kelvin lattice structure were evaluated. Build qualitywas evaluated using the digital microscope and scanning electron microscope (SEM).As well as to evaluate the behavior and mechanical properties of the kelvin lattice structure,quasi-static compression test was performed. Finite element modeling was carried out to predictthe mechanical properties and behavior of the kelvin lattice structure. To do this, the unit cellmethod was used. Based on the provided images, the kelvin lattice structure was fabricatedwithout defect and in accordance with the previously defined geometry. The experimentalcompressive test results show the favorable mechanical properties, the ability to absorb energy,and the excellent reproducibility of the fabricated lattice structures results. Finite elementmodeling had a good agreement with experimental results which can be used to predict thebehavior and mechanical properties of the kelvin lattice structure with much less time and costthan the experimental method.

In this paper flexural vibration and buckling analysis of the viscoelastic nanotube under electromagnetic force is investigated analytically. In order to consider more realistic assumptions, the linear solid viscoelastic model is used. The differential equations of motion are derived via the nonlocal Timoshenko beam theory. The Lorentz magnetic force is obtained from the Maxwell's relation. The analytical method is used to obtain nonlocal natural frequencies and buckling load of the system. The influence of magnetic field, aspect ratio and nanoscale effects on the natural frequencies and buckling load are studied. Then the results are validated and illustrated with appropriate figures and tables.

An Acrobat robot is a two-link surface robot that emulates the behavior of an acrobat man. This paper designed a dynamic output feedback control strategy to overcome system challenges such as its balancing and swing. This method is employed for the optimal control of the nonlinear model of the acrobat robot. It is important to note that dynamic feedback controllers are preferable to static ones due to their more effective control performances alongside with more degrees of freedom in achieving control objectives. In addition, the presented approach is incorporated with fuzzy control to optimize and update the parameters of the proposed controller. Simulations are performed in several cases consisting of the nominal system and considering the noise and disturbances. Simulation results demonstrate that the proposed controller in the form of fuzzy dynamic output feedback has a good performance compared to the static and dynamic output feedback in various situations.