Mechanic of Advanced and Smart Materials

Abstract The wheeled mobile robots have many applications due to their advantages such as wide workspace, mobility and maneuverability. Intelligence of mobile robots to perform autonomous movements is also one of the favorite fields of robotics researches. In this paper, the trajectory tracking of an intelligent mobile robot on a sloping surface is studied using a nonlinear sliding mode control. First, the nonlinear dynamic equations of a wheeled mobile robot are derived on a sloping surface using the Newton-Euler method. A multistage nonlinear control block is then proposed for trajectory tracking. First, the controller calculates the linear and angular velocity of the robot to find the position of the robot, and then, assuming uncertainties in the dynamic model, a sliding model controller is used to track the robot's specific path. Various simulations are presented to validate the control method, which the results show the capability and efficiency of the proposed method.

Abstract One of the major limitations of using Terfenol-D in actuators and sensors is its magnetic hysteresis power loss which leads to reduction of mechanical power loss, precision and linear measuring range in actuators and sensors, respectively. In this paper, magnetic hysteresis power loss of Terfenol-D and its affecting parameters are studied and modeled experimentally. To this end a fabricated experimental setup is used to obtain magnetic behavior of Terfenol-D consisting of major and minor hysteresis loops at different values of frequency, magnetic field intensity and mechanical pre-stress. Data of these loops are used as an input to analytical equation of magnetic hysteresis loss. The results show that the magnetic hysteresis loss increases with increasing in frequency and peak value of magnetic field intensity and decreasing in mechanical pre-stress. Then, an explicit model based on power relations for frequency, peak value of magnetic field intensity and mechanical pre-stress is presented to predict magnetic hysteresis power loss. This model is validated under new different conditions and the results show very good agreement with analytical model. The main advantage of the explicit model is that it does not need hysteresis loops as input data and it can predict the magnetic hysteresis power loss only by determining the values of conditional parameters.

Abstract In this paper, static bending and buckling due to different distributions of functional porosity based on Timoshenko's beam theory are investigated. The modulus of elasticity and mass density are considered according to the two patterns of specific porosity distribution in the direction of thickness. The partial differential governing equations are derived from the minimum potential energy principle. The Ritz method is used to calculate the critical buckling loads and transverse bending curvature. The obtained results have been compared with other references and also finite element modeling. A parametric study was performed to investigate the effects of porosity coefficient and slenderness ratio on buckling and flexural properties of porous beams with pinned boundary conditions. Also, the effect of different porosity distributions on structural performance has been investigated to obtain essential insights into the design of this type of beam to achieve the desired buckling strength and flexural behavior. According to the parametric study results, increasing the porosity coefficient and slenderness ratio increases the critical buckling load and the bending strength. This research results can design poros beams like metal foams or recent manufacturing methods like additive manufacturing. Among the applications of the present study, this type of porous material for bone repair scaffolding can be mentioned.

Abstract In recent years, gecko-like dry adhesives have been used in robotic grippers and climbing robots. The adhesive has been introduced as a new approach for manipulating flat objects in production lines. The method has several advantages over other, more traditional, gripping methods such as lower power consumption compared to suction-based systems or the ability to handle non-magnetic materials. Directional Gecko-like adhesives are based on the frictional adhesion and employ asymmetric feature, mostly wedge shape, and perform only in one direction. In this paper, design and fabrication process of a new pyramid shape Gecko-like adhesive using silgard 184 has been described. The new microstructures has the ability of adhesion in several directions, and the contact surface between the adhesive and substrate increases and the possibility of self-sticking between adjacent stalks decreases. Chemical machining and microlithography were used for manufacturing molds in this research and the details were described. The performance of proposed adhesive was evaluated using an experimental set-up and adhesion force was measured on different substrate. During experiments, adhesion was controlled via applied shear force to adhesive. The experimental results showed 30% increase in adhesion using proposed adhesive in comparison with the existing similar adhesive.

Abstract Acceptable fatigue life assessment of components is desirable for various industries. The fatigue life of a specimen includes the total number of cycles required for crack initiation and the number of cycles required for crack growth. In many industries, such as aerospace or petrochemical and refining industries, due to the high cost of parts, it is necessary for the part to continue to work even after crack initiation. Therefore, to estimate the fatigue life, the fatigue crack propagation should be studied. Experimental fatigue tests are very time consuming and costly. So, it is very important to use finite element software to simulate and study the fatigue crack growth. In this research, with the help of finite element simulation in Abacus software and using the J integral criterion, the growth of fatigue cracks and the estimated life of a sample of 5000 series aluminum alloy was investigated. The results were compared with experimental data and a good agreement was observed.

Abstract One of the ways to convert mechanical energy into electricity is the use of triboelectric generators. In this paper, we have tried to discuss the principles of these generators and improve their performance, as well as present new structures for their use. The most important research on improving performance, including improving materials, improving surface geometry, improving structures, and more. A solution is proposed to improve the surface geometry, which involves changing the angle of the double-corrected surface by sandpaper with different grit sizes. The output voltage was investigated for different angles of adjustment of the two modified tribo surface relative to each other, including a PVC surface and another surface of aluminum. It was found that the produced voltage for the two-page placement ratio with non-zero polishing angle in different grit sizes of sandpaper was significantly improved in comparison with zero-degree mentioning in previous studies. Next studies will follow applications of this technology.

Abstract In this paper, the optimization of effective parameters on the process of severe plastic extrusion deformation in the torsional angular channels of the plate is investigated. Initially, the process test was designed using the response procedure method, and four main and influential input variables on the process, torsion angle, radius, channel angle, and coefficient of friction, were extracted, and the regression equations of each for the mechanical properties of the samples produced by this method. Using sensitivity analysis, which is very useful in the production of parts and industry today, and by using it, the quality of manufactured parts can be greatly improved and production costs can be reduced to a large extent, the effect of input variables on plastic strain Parts checked. In this paper, the mean and maximum strain and maximum force, which are defined under the influence of these input variables, have been investigated and analyzed using the e-Fast statistical sensitivity analysis method. The results of the analysis show that the mean strain is affected only by the values of torsional and channel angles, but the maximum strain is affected by the coefficient of friction and has a direct linear relationship with its changes. The maximum force is also in a balanced state from the effect of the variables. Also, the quantitative effect of torsion angle of 52% and channel angle of 48% on mean strain and coefficient of friction with 86% and torsion angle with 42% had the greatest effect on the strain and maximum force.