مجله مهندسی مکانیک
سال پنجاه و یکم شماره 3 (پیاپی 96، پاییز 1400)

Work piece surface roughness as one of the most important output parameters of the machining process has a significant impact on the final cost of production. Parameters such as cutting edge sharpness, vibration and cutting tool wear have a great effect on the surface roughness of the work piece. In this paper, the effect of cutting tool cryogenic treatment on tool wear and work piece surface quality in different machining parameters (cutting speed, feed rate and depth of cut) was investigated and compared with dry and conventional (wet) turning of AISI 304 austenitic stainless steel. The Taguchi method for design of experiments and the signal-to-noise ratio method for analysis of results were used. According to the obtained results, the wear of the cryogenic treated tool was reduced compared to the cutting tool in dry and conventional machining modes. The surface roughness of the work piece in machining with the cryogenic treated tool is less than in the dry and conventional machining modes due to reduced tool wear and preserving the sharpness of the cutting edge of the tool.

Continuum robots have better maneuverability than conventional serial manipulators with rigid arms, especially in confined environments. Inherent compliance of these robots is caused a better interaction with objects that are facing their presentation. In these robots, cables that are connected to disks are used as actuators. In this paper, the kinematics of a driving-cables continuum robot is studied at first. Using the equations obtained in kinematic analysis, dynamic analysis is performed and the equations of motion of the robot are derived. Due to the uncertainty of the dynamic model, a robust controller is suggested. In the proposed method, the nonlinear functions related to the Coriolis, the Centripetal and gravity force are estimated using by the radial neural network and the Projection operator and their approximation are used in the controller. To verify the performance of the proposed controller, some simulations are performed. The results show that the proposed controller can force the continuum robot to follow the desired trajectory without knowing the nonlinear terms of the dynamical model.

Quadrotor is one type of unmanned aerial vehicles which it's maneuverability and simple structure has extracted fascination. In spite of this, its highly non-linear behavior can be regarded as one of its disadvantages. The dynamic model of quadrotor is nonlinear with many sources of uncertainty, so in the controller design process, robust control methods such as sliding mode, are required in order to achieve good tracking and stabilization results. In contrast to the high capabilities of sliding mode control approach, high frequency switching of the control signal, is considered as one of its disadvantages, which can be reduced by using higher order techniques. In this paper the behavior of the both first order and second order sliding mode controllers in, trajectory tracking of the position and the yaw angle to their desired values and stabilization of the roll and pitch angles of the quadrotor, under high uncertain conditions, are investigated. The second order sliding mode control was designed based on super twisting algorithm. Considering high parametric uncertainty in quadrotor data, the comparison between the results of the two methods, shows the good performance of the second order sliding mode control, in terms of tracking, stabilization and chattering reduction.

Heat pipe is a two-phase heat transfer device with extremely high thermal conductivity. The structure of a heat pipe is practically divided into three regions: a) the evaporator region at one end of the pipe where heat enters to this region, b) the condensation region at the other end of the pipe where heat is excreted in this zone, and c) the adiabatic region, includes the evaporator and condenser regions. In this research, the forming process of grooved heat pipes in mini/micro dimensions by extrusion is numerically simulated and the possibility of production by extrusion process is investigated. During the numerical simulations, the value of force required for forming and the effect of variables such as pipe material, pipe diameter, pipe length, number of grooves in cross section and groove profile are studied. Additionally, the mutual effects of the parameters on each other have been identified and proper values of some parameters such as extrusion process velocity and groove profile type are determined.

In the present study, semi-energy and FEM method have been done to determine the buckling behaviour of rectangular glass-epoxy composite with a central cut-off to demonstrate the accuracy of experimental results. The experimental results have been derived by an innovated SS-FF fixture. The effect of cut-off diameter and the number of layers on buckling load were investigated. For thin laminated composite plates subjected to pure loads, the buckling loads of these three methods are approximately equal. However, in the buckling analysis of thick laminated composite plates, experimental results having a little distance from FEM and semi-energy results. The results show that the buckling load decrease and increase with increasing and decreasing of cut-off diameter and the number of layers respectively. However, in the buckling analysis of thick laminated composite plates, experimental results having a little distance from FEM and semi-energy results. The results show that the buckling load decrease and increase with increasing and decreasing of cut-off diameter and the number of layers respectively.

Milling process of the thin-walled structures has broad applications in aerospace, automotive industries and etc. One of the main problems in their machining is unstable chatter vibrations, which causes not only the poor machined surface quality but also decreases the system life span and machining efficiency. So, lots of researchers are interested in investigating the dynamic behavior of the thin-walled structures during the machining processes and restrain its pernicious effects. In this regard, the main purpose of this paper is to l the effects of geometrical parameters of machining system including workpiece height, thickness, and tool overhang and its diameter on the chatter stability. To this end, first by utilizing relative transfer function concept, dynamic models of tool and workpiece were derived. Then experimental tests conducted to extract cutting force coefficients. Finally, stability lobe diagrams were constructed under impression of tool and workpiece dimensions. Results proved that by increasing tool overhang length, chatter stability decreases.

Use of Oscillating Heat Pipes (OHPs) as a new technology in the heat transfer field has been of interest to different industries in recent years. In this experimental investigation, the thermal performance of a newly designed three-dimensional oscillating heat pipe with Fe3O4 nanofluid exposed to a magnetic field under different input power (0–450W) is investigated. The results showed that the device had a better thermal performance at a filling ratio of 50%. Although the OHP has been applied in many fields, the three-dimensional OHP has not been investigated widely so far. The use of iron oxide nanofluid (Fe3O4) significantly improves the thermal performance of the oscillating heat pipe especially in a filling ratio of 50% compared to pure water. Also, the results show that the use of a corrugated evaporator will increase the heat transfer coefficient. The corrugated evaporator pipes have better thermal performance compared to the simple pipes. Also, when the evaporator is exposed to a constant magnetic field, the thermal performance of the device improves significantly.

In this paper, the purpose is to improve the performance of the Imperialist Competitive Algorithm. Local search is added to the algorithm and this is done in two stages. In first stage, selection of the initial optimization parameters for starting the problem is done wisely and the population is leaded to optimal point. In second stage, after each 10 iterations a local search is performed between colonies and the imperialist of some of the strongest empires, in order to gain more accurate answers while not making a notable change in the process of reaching the answer. This method is not applied to all empires, so that calculations would not overflow. The proposed algorithm is tested using benchmark functions and based on the comparisons, the performance of the initial algorithm is much more improved when dimensions of the optimization problem goes higher. With few unknown parameters, conversion time and final minimum values are close in both methods, but by increasing the dimensions of the problem, even in some cases total calculation time is reduced to a half and the accuracy of minimum value is improved by 10 orders of magnitude. At the end, one application of the method is investigated in finding the suitable control gains for controlling a helicopter, which is a relatively a new application, and the performance is evaluated comparing to pole-placement and by state-feedback control.