مجله مهندسی مکانیک امیرکبیر
سال پنجاه و چهارم شماره 12 (اسفند 1401)

In this paper a new application of Stewart platform is developed for rehabilitation utilities. Here the Stewart model is modified in order to be employed as a wrist rehabilitation robot and is controlled using a nonlinear position approach. To meet this goal kinematics of the robot is extracted using Jacobian matrix. Afterwards, the related dynamic model of the proposed robot is developed using virtual work method. In order to keep the wrist of patient within the desired path of rehabilitation a nonlinear position control is designed and implemented on the robot using Computed Torque Method (CTM). In order to move the patient wrist along a safe path an optimal path in extracted through which the least amount of acceleration and consequently interaction force will be implemented on the wrist and this path is controlled using the designed controller. By the aid of conducting some analytic simulations in MATLAB the applicability of the proposed robot for wrist rehabilitation is demonstrated. The verification of the model is performed by comparing the results with previous articles while the efficiency of the implemented controller is proved by comparing the actual path with the desired one in presence of disturbance. It is shown that by the aid of the proposed robot and controller, the wrist rehabilitation process of a patient can be successfully accomplished.

In this paper, to increase the navigation accuracy in the integrated Global Positioning System (GPS) and Inertial Navigation System (INS), a new direct filtering approach called Interacting Multiple Model-Refined Strong Tracking Extended Kalman Filter (IMM-RSTEKF) has been developed. In the proposed method, while using inertial navigation equations and tracking equations in order to improve the accuracy of position and velocity, to increase the accuracy of orientation, attitude estimation methods based on the gyroscope, accelerometer and GPS have been used. In addition, in order to enhance the Extended Kalman Filter (EKF) robustness against modeling error, the Refined Strong Tracking (RST) method has been used. The aircraft then verified the proposed method using data collected in a real field experiment. The results of the proposed method were compared with the results of conventional indirect filtering method Kalman Filter (KF), direct filtering Unscented Kalman Filter (UKF) and IMM-EKF. The results show the more accurate performance of the proposed method compared to the previous three methods in the GPS/INS integration.Keywords: Global Positioning System, Inertial Navigation System, Extended Kalman Filter, Direct Filtering, Multiple Model Estimate, Interactive Multiple Model.

One of the most important challenges in using active vehicle suspension systems is the high energy consumption of these types of systems. The use of the electrical energy harvesting system is one of the ways to reduce energy consumption in active suspension. In this article, by designing a new optimal controller of the vehicle active suspension system and the electric energy harvesting system, the interaction of them has been investigated. The active control loop calcultas the required force to realize the desired mechanical performance and is based on the constrained nonlinear predictive control algorithm that is obtained from the continuous model of the system. Also, the mechanical indexs of the suspension system, including travel comfort and roadability, are managed by weight coefficients defined in the active control algorithm. The effect of the weight coefficients of the active control algorithm in such a way to have the maximum harvesting of electrical energy at the same time as achieving the desired mechanical performance is another issue that has been addressed in this article. The results of the simulations for two types of road show that the correct use of the active control algorithm governing the problem leads to the realization of the desired mechanical performance combined with the maximum harvesting of electrical energy and the external energy consumption of the active control system is significantly reduced.

The purpose of this study is to present a method for controlling an inverted pendulum in the presence of nonlinear and indeterminate friction force between the moving cart and its straight guide rail. Control of an Inverted pendulum, as an Under-actuated Mechanical System, is facing challenges from theoretical and experimental aspects. To deal with such challenges, a new method is proposed in this paper. The method is based on an approximate input-output linearization of the inverted pendulum dynamic model for which a modified sliding mode control is proposed. For experimental determination of the bound of friction force, an inverted pendulum with a moving cart is designed and built. The moving cart and its rail are intentionally designed and built such that the resulting friction force is nonlinear, uncertain, and state-varying. The upper bound of the friction force is obtained experimentally and its average value is added to the control input obtained from the conventional sliding mode controller. Experimental verifications depict the success of the proposed control method in preserving the closed-loop stability under the challenging case of dealing with a large nonlinear friction force.

Studies on the behavior of dielectric elastomers, as a class of electroactive polymers, often focus on hyperelasticity and dielectric property. However, expanding the use of these materials as actuators in industry depends on a better understanding of the factors affecting their behavior, including viscoelasticity, as well as the possibility of adding new properties such as anisotropy to these elastomers.In this research, using the development of basic relations in continuum mechanics and consideration of governing equations, a nonlinear coupled model for describing the behavior of anisotropic hyperviscoelastic material with dielectric property is presented. First, the presented model was evaluated by step-by-step comparison between the results of its component and experimental results reported in the available literature. Good agreement between the results indicates the accuracy of the model in describing behavior of the materiel. Then, using comprehensive form of the model, for an incompressible material with hyperviscoelastic, anisotropy and dielectric properties, we studied the effect of loading rate and electric field on the behavior of fiber-reinforced elastomers at different fiber angles. Obtained results from applying the model to a sample problem show that increasing fiber angles reduces the stress range, and increases the effect of loading rate and electric field.

Major bone defects, especially in long bones such as the femur, which can result from trauma, tumor, or bone infection, are among the most common injuries a person faces daily. This research presents a practical and accurate process for designing bone tissue engineering scaffolds to treat bone injuries. For this purpose, CT-Scan images of the area related to the human femur were obtained. A bone defect caused by bone damage was made in the cortical and trabecular parts. Next, the outer surface of the damaged parts was designed with an ideal geometry. The design of the unit building cell of the internal structure of the scaffold was also done with simple cubic geometry. Finite element analysis was used to investigate the effect of porosity on the Young modulus of the unit cell. Finally, using the results of finite element analysis, a unit cell with an edge size of 0.972 mm and pore size of 0.6 mm was designed to reconstruct the cortical part, and a unit cell with an edge size of 0.972 mm and a strut thickness of 0.165 mm was designed to rebuild the trabecular part. The scaffold designed in this study has a geometry that matches the geometry of the damaged part in its ideal state and provides the necessary conditions for cell proliferation and diffusion of nutrients.

Dragonfly wings have an interesting biological composite structure and are very specialized flight organs that are well adapted for the flight behavior of each dragonfly. This paper aims to investigate the effect of graphene nanoparticles on the strength of a sandwich structure inspired by the dragonfly wing configuration under quasi-static loading. The streak structures are made of glass/epoxy layers with different percentages of graphene nanoparticles. Also, polyurethane foam was used in the central core of the vein. The crashworthiness characteristics of these structures were discussed. On the other hand, the effect of polyurethane foam on the damage rate of sandwich veins due to quasi-static loading was investigated. In order to investigate the damage in sandwich structures, pictures of the damaged surface and the cut view of the damage were taken, and the results were reported. Finally, FE-SEM analysis was used to evaluate the distribution of graphene nanoparticles in the polymer structure. The results of this study show that the presence of graphene nanoparticles in the sandwich structure resin with foam core will not have much effect on the strength of the structure if it is less than one value. On the other hand, if the amount of graphene nanoparticles in the resin of this type of structure exceeds a certain amount, it shows relatively good resistance.

This paper discusses the failure phenomenon of the welding joint for the flight bars in a rotary dryer under impact loading. The flight bars are utilized to provide a curtain of particles and to avoid direct cohesion of the production to the steam tubes. In addition, some gravitational hammers knock off the shell outer skin to fall off the product buildup from the shell inner surface. The condition monitoring has revealed that periodic impacts of hammers on the outer skin will result in welding joint failure between the flight bars and the shell followed by a complete detachment. Assuming that the hammer impacts the shell by a constant rotational speed, the finite element software is employed to simulate the mentioned problem. The results indicate severe stress concentration and plastic deformation around the roots of welding joints. To prevent joint failure, different mechanisms are proposed such as: relocation of the welding joints, employment of the stiffening angles and an increase in the thickness of the absorbing pad. The outcome of current study showed that relocation of welding joint toward the flight bar end and the application of stiffening angle can decrease the maximum vonMises stress by a factor of 18% and 43%, respectively. Moreover, using a composite absorbing pad will decrease the vonMises stress level up to 80% around the roots of welding joint.

The flaring of the ends of thin-walled tubes is a subset of SPIF, which is considered by researchers due to its high flexibility and application in the field of RP. Considering the few studies that have been done in the field of dimensional control of the produced products by this process, in this research, the experimental study and statistical analysis of the variables affecting the end diameter of formed tubes were considered. In the present paper, the DOE was done based on the RSM. In order to forming the end of AISI 304 steel tube, process input variables including: tool diameter, tool angular step, tool vertical step and type of lubricant were selected. Then the effect of input variables on the tube end diameter was analyzed. Also, the function of the response parameter was extracted from the input variables in terms of linear, interactive and quadratic expressions, and its competency and adequacy was confirmed. The ANOVA results showed that the expressions of the V, D and the interactive effect of DA are the most effective expressions on the tube end diameter. Finally, the optimal combination of process input variables to achieve the maximum of the tube end diameter was determined using the desirability method, and by running the verification test, the correctness of the regression equation to predict the response parameter was confirmed.

The present research has investigated the fatigue life of in-service steel patch welded joints by experimental/numerical approaches. To this end, three types of welded panels with similar WPS but different cooling conditions were constructed. Subsequently, test samples cut from the main panels were subjected to fatigue tests. A novel approach involving continuous hardness measurement at the welding section was employed to predict the mechanical and fatigue properties of different zones in welded specimens. Firstly, the mechanical properties and fatigue parameters of various weld regions and HAZ were calculated by microhardness measurement and metallography images. Then, stress analysis was conducted in the Abaqus. The fatigue life was predicted using the stress and strain values obtained from the FE analysis, the UVARM subroutine, and multiaxial fatigue modeling codes. The life estimations obtained from the numerical models were ultimately compared by experimental fatigue test results. The experimental tests showed that the samples cooled with water at a speed of 0.5 m/s had an increase in life, and the samples cooled with water at a speed of 1.5 m/s had a decrease in life compared to the samples cooled in air. Moreover, to predict the fatigue life, Brown-Miller-Marrow and Glinka criteria were used, respectively, and the results showed that these two criteria are able to predict the fatigue life with the maximum average error of 20.16% and 34.68%, respectively.

Composite laminates are advanced engineering materials which are widely used in various industries due to their unique properties. The aim of this paper is to assess the effect of electrospun nanofibers on the fracture and fatigue behavior of composite laminates and also to investigate the performance of Finite Element Method (FEM) based on Cohesive Zone Model (CZM), in predicting the fatigue behavior of the laminates. For this purpose, standard specimens were fabricated from carbon/epoxy Prepregs interleaved with nylon 6,6 nanofibers. The specimens were then subjected to mode I static and fatigue loading conditions. The results showed that fracture toughness was doubled by adding nanofibers between composite layers. Under fatigue loading, the crack growth rate of the nanomodified specimens was less than the virgin specimens. So that, crack growth rate decreased 8 times by interleaving the nanofibers in . The CZM method was used to evaluate the efficiency of finite element in modeling the fatigue crack growth rate in virgin and nanomodified specimens. The progressive failure model was used to simulate the fatigue behavior. Consistency of FE results with the experimental results showed that the CZM method is a suitable tool to model the fatigue behavior of interleaved composite laminates.

In this study, the microstructure and mechanical properties of dissimilar joining of Inconel 718 superalloy to 316 austenitic stainless steel were investigated using tungsten-gas arc welding method with two filler metals 718 (ERNiFeCr-2) and 625 (ERNiCrMo-3) . After welding, the microstructure and mechanical properties of different joint areas were evaluated using optical microscope and scanning electron microscope. The precipitates in the interface and their chemical composition were determined using EDS analysis. Also, the mechanical properties of the joint were evaluated using tensile, impact and microhardness tests. Microstructural investigations showed that the freezing structure of filler metal 718 has austenitic microstructure with dendritic network along with carbide distribution and filler metal 625 has also created austenitic microstructure with dendritic network. In the tensile test, filler metal 718 has the highest tensile strength of 528 megapascals and the failure of all tested samples occurred in the area of the austenitic stainless steel base metal 316. The results of the impact test showed that the maximum amount of fracture energy is 50 J for filler metal 625. The micro-hardness test also determined that the 718 filler metal has the highest hardness of 214 Vickers.