Mechanic of Advanced and Smart Materials

Abstract In this research, the frequency characteristic equation for some non-uniform and homogeneous beams based on Euler-Bernoulli beam theory is presented in closed analytical form. At both ends, the beam carries objects with deviations from the center, mass moment of inertia and linear and rotational elastic constraints. Therefore, the closed analytical characteristic equation has the ability to provide frequency parameters for a wide range of non-classical boundary conditions. Solving the governing differential equation and applying boundary conditions leads to the solution of an eigenvalue problem. Since the beam is non-uniform, the exact solution of the governing differential equation depends on finding a closed analytical solution for the beam deflection. Therefore, a limited type of non-uniform beams can be accurately solved. In order to verify the validity and accuracy of the presented relationships, the results of the method presented in this research have been compared with the existing results for uniform beams. Also, the mode shape of the deflection are given for a beam sample.

Abstract In this paper, buckling analysis of functionally graded rectangular Nano-plates considering the surface effect is investigated. Also, to define the material properties the Mori-Tanaka scheme is used which according to this scheme the material properties change continuously along the thickness direction. Displacement field is obtained using modified shear deformation theories. In these theories, against classical plate theory, the effects of rotary inertia and transverse shear deformations are considered and various functions such as exponential, trigonometric, hyperbolic and parabolic functions are used to considering these effects along the thickness direction. To considering nonlocal and surface effects the nonlocal elasticity theory and surface elasticity theory are employed respectively. The governing equations of motion are obtained by Hamilton’s principle and the Galerkin method is used to solve these equations. To show the accuracy of the present formulations, the presented results in this thesis are compared with those reported in the literature. Finally, the effects of various parameters which is related to the surface parameters such as residual surface stress, surface elasticity constant and also other parameters such as thickness ratio, aspect ratio, material index and nonlocal parameter of functionally graded nano-plate are investigated.

Abstract As a subset of mobile robots, the tractor-trailer mobile robot has been widely used in various applications in the past decades, including military and civilian missions, due to its advantages, such as a more expansive working space, high maneuverability, and load-carrying capacity has been used. One of the main challenges in controlling the tractor-trailer robot's speed is the tractor drives' dynamics. In this article, to complete the modeling after investigating the kinematic and dynamic equations governing the tractor-trailer robot, coupled dynamics have been presented by considering the dynamics of the tractor wheels. In the following, using the coupled dynamics, a suitable controller has been designed to control the robot's speed to achieve the desired value and the position point by point. Various simulations are presented to demonstrate the dynamic performance and the proposed controller. According to the simulation results, the presented theory improves the performance of the designed control system.

Abstract The deep drawing process is one of the most widely used metal forming methods, which is widely used in the mass production of parts. The phenomenon of earring has always been one of the defects in deep drawing processes, which causes an increase in material waste and a decrease in the production speed of parts. This phenomenon is caused by plane anisotropy resulting from the cold rolling operation. One of the methods to reduce the earring defect is to optimize the initial blank. In this article, a method to optimize the initial blank and to reduce the earring defect in the process of deep drawing of square sections is presented. For this purpose, the initial blank made of SAE 1015 steel was simulated in Abaqus software. In the following, by using the particular objective function, the initial blank was radially optimized in specific paths. By re-simulating the optimal blank and checking parameters such as; Thickness changes, stress distribution, and strain changes, it was found that if the optimal blank is used, the earring defect is significantly reduced

Abstract Drilling is one of the most common methods during surgery on human bones with the aim of keeping broken bones together. Due to the complexity of the material under the machining process and the sensitivity of the process, it is one of the most important and widely used mechanical methods in the field of medical engineering. Cracking, breaking and serious damage to bone tissue is a problem that may arise with increased machining forces during orthopedic operations. In this article, a second-order linear regression equation was presented in order to predict the behavior of drilling forces in terms of feed speed, tool rotational speed, drill diameter and their effective interactions. Also, to check the influence of each parameter, E-fast sensitivity analysis method was used. According to the obtained results, the rotational speed of the drill is the most effective input parameter on bone drilling forces with 57% influence. After that, the feed rate with 23% and the cutting depth with 20% are the parameters affecting the force in the bone drilling process.

Abstract In a variety of industries, thermosyphons are used to improve heat transfer. High reliability, easy maintenance and repairs, high thermal conductivity, and isothermal heat transfer are among its benefits. Thermosiphon is used for a variety of things, including cooling electronic components and air conditioning. In the studies conducted on the thermal performance of thermosyphons, it has been determined that the type of working fluid is very important. For this purpose, in this research, the thermal behavior of thermosyphons using two different working fluids has been investigated experimentally. A copper tube with a length of 1000 mm, an external diameter of 22 mm, and an internal diameter of 20 mm is used to construct the thermosyphon previously mentioned. The thermosyphon was tested with two working fluids—methyl acetate and deionized water—and three filling ratios—55%, 70%, and 85%—along with thermal loads ranging from 50 to 300 W and at a distance of 50 W. The results of the experiments revealed that this thermosyphon had a lower thermal resistance in the filling ratio of 70% of both fluids. Additionally, methyl acetate outperformed deionized water in terms of thermal performance by about 20–50%

Abstract Considering possible plastic deformations for metals such as steel during design calculations reduces metal consumption in practice. In general, structural elements with heavy loads, such as shells of building structures, rockets, chemical reactors, thin-walled pipes and other structures, are designed using computational methods, in order to properly and scientifically design, plastic deformations should be considered in them. Laser welding is one of the most important and sensitive types of welding in metals, which has many applications in various industries. In the present study, the effects of laser processing on the mechanical strength of steel sheets and their resistance to bending loads caused by laser radiation have been investigated. The results of bending tests and computer simulation of elastoplastic deformation show that st37 carbon steel sheet subjected to local laser processing with surface melting due to increased mechanical strength can be used as a suitable replacement for more resistant and expensive alloys in advanced industrial and military applications.