مجله مهندسی مکانیک امیرکبیر
سال پنجاه و چهارم شماره 6 (شهریور 1401)

The energy from vibration can be used as a source to generate voltage. The use of a vibration absorber can minimize the vibrations of the structure and at the same time be used as an energy harvesting . In recent years, the use of intelligent materials capable of generating voltage has made significant progress in various fields, including microelectromechanical systems. In the present study, a continuous beam containing a layer of magnetoelectroelastic smart materials has been used as a dynamic absorber. This absorber with piezoelectric and piezomagnetic properties both helps to reduce the vibrations of the system by one degree of freedom and extracts energy from it. Considering a harmonic excitation force applied to the main system, the general absorber equations were extracted and the effect of different beam parameters on energy harvesting was investigated. Using optimization method and using genetic algorithm, appropriate values were obtained to achieve both goals The experimental response surface methodology was used to find the cost function. The studies were performed in the first three modes of Bernoulli Euler beam and it was found that the subsequent modes have little effect on the generated power. In fact, the highest energy harvesting occurred in the first mode and in the frequency range of 10 to 40 Hz. The vibrations of the main structure also decreased by about 65%.

In industrial rotatory machines different forces in rotor bearings are generated due to various impaired mechanical sources, namely bearing misalignment and nonhomogeneous mass distribution (unbalance). By precisely analyzing and diagnosing the produced patterns of bearing forces, one can determine the unbalance parameters such as quantities of masses, their distance from the rotational axis, and characteristics of corresponding parallel planes. Consequently, it will be possible to formulate pragmatic protocols according to which the maintenance engineers of rotatory systems will pinpoint properties of problematic imbalance masses and then straightforwardly balance them. In the procedure of conducting this research several exemplary imbalance masses are deployed on a rotatory mechanical shaft and the equations of motion and forces in perfectly aligned rigid bearings are extracted. Then, by applying a neural network-oriented system the patterns of bearing forces are recognized and the characteristics of the nominal masses including magnitudes, distances from the rotational axis, angles as well as the unbalance type are determined. The accuracy of predicting 8 variables of balancing masses was 41% and after eliminating the redundant overlaps from principal components, the accuracy of predicted 5 variables of balancing masses significantly increased to 95%. Also, by implementing another comprehensive neural network system, it was shown that by exerting two separate balancing masses, the applicability of this method in balancing any faulty systems with dynamic unbalance is possible.

Thin Walled Beams are widely used in engineering applications with the minimum weight design criteria. Frequently used thin walled beams have low torsional stiffness and their torsional deformations may be of such magnitudes that it is not adequate to treat the angles of cross section rotation as small. In this paper, nonlinear torsional vibrations of thin walled beams will be investigated. The method of multiple scales will be implemented as solution method and different nonlinear phenomena will be studied. The obtained results are compared with the available results in the literature which reveals an excellent agreement between different solution methodologies. The outcomes of this study show that beam nonlinear torsional dynamics and the related phenomena could influence the linear torsional dynamic of beams under axial load, e.g. rotating beams. Forced torsional vibrations of beam with the excitation in the form of primary resonance of first and second mode have been investigated. It has been demonstrated that in the case of beam with two ends clamped boundary conditions, three-to-one internal resonance will be appeared. The primary resonance of first and second mode have been solved in two sets of boundary conditions, torsionally clamped-fixed and torsionally fixed-fixed. Nonlinear response, amplitude-phase equations, fixed points and their stability have been studied.

In the present study the nonlinear vibration behavior of a beam with general boundary condition carrying an electrical current and subjected to a magnetic field is investigated. The magnetic couple, transverse magnetic force, electrical current and the damper are considered in this paper.. Hamilton’s principle and Maxwell equations are applied to obtain the governing equation of the system under certain hypotheses. Also, the Galerkin’s method is used to solve the solution of the elastically restrained beam carrying an electrical current subjected to magnetic field. Thus, the effect of the rotational and the translational support flexibilities, the magnetic field and other parameters are evaluated. Finally, some numerical examples are shown to present simplicity and efficiency of the presented formulation. It can be concluded that the effect of the magnetic field reduces the deflection of the system and it decreases the natural frequency. On the other hands, it can be seen from the results that the deflection of the beam respect to various magnetic field are indicated the significant effect of the boundary conditions, not only on the dynamic response of the damped beam, as well as, also on the rate of damping of the response. Based on the results, the dynamic response under the magnetic field is decreased when the beam experiences a stiffer constant in its supported on the beam.

This paper proposes a novel hybrid control framework by combing enhanced extended state observer (EESO) with trajectory linearization control (TLC) for air-to-air missile acceleration tracking problem. First, based on the tracking error dynamics derived by Taylor expansion for the original nonlinear system along the desired trajectory, a feedback linearization (FL) based control law is designed to stabilize a linear time-varying (LTV) system. To reduce the controller performance sensitive to uncertainties, with partial model information, EESO is constructed to estimate the tracking error vector, as well as the uncertainties in an integrated manner. The closed-loop stability of the system under the proposed compound scheme is established. Both numerical simulation studies and an application example of missile acceleration autopilot design demonstrate the feasibility and efficacy of the proposed method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The present paper has been dedicated to finite element simulation and experimental study of cutting tool temperature during laser assisted machining. To achieve this objective, a finite element model of the processes has been developed for Inconel 718 super alloy and the results have been verified by experimental measurements of cutting forces and cutting tool temperature. In this regard, first of all a finite element model of laser assisted turning process was developed and then experimental setup was designed and manufactured. Finally, a series of experimental tests were arranged to achieve proper range of process parameters and also to measure cutting forces and cutting tool temperatures during the machining process. Experimental results were then used to verify the results of finite element model. Using the developed model, the effect of laser source power, cutting speed and feed on cutting tool temperature were studied. According to the achieved results, using laser heat source, in the range without micro structural effects, will lead to 25% reduction in the average of main component of cutting force and 80% reduction in the average maximum temperature of cutting tool in comparison to conventional turning.

To study the energy absorption features in composite structures, it is necessary to identify the functional mechanisms of absorption and to determine the impact of each on the amount of energy absorption.In this study, the behavior of composite tubes under quasi-static compressive load by monitoring acoustic emission signals has been investigated.For this purpose, to make a filament wound composite tube, optimal parameters were first determined using the researches.In determining the optimal parameters, due to the uncertainty in the effect of the angle of fibers, from the optimal range of the intermediate-range, namely the angle of 35 degrees, was selected and investigated using the acoustic emission method.To ensure the experimental results, the finite element simulation method of ABAQUS software was used, and the VUMAT subroutine based on the Hashin criterion was implemented.The functional behavior of the tubes in this ply angle showed that the dominant failure mode was a local shear failure and lateral damage, which first caused the plastic deformation and then caused cracks to grow in the fiber direction.Also, the results of acoustic emission showed that the highest percentage of failure mechanisms are matrix cracking, fiber breakage, and debonding respectively.Finally, the use of the developed subroutine to predict the behavior of the structure was useful and was able to predict the behavior of the composite tube even after the maximum crushing force.

This study investigates the construction of polymer/graphic composite bipolar plates via hot compression molding for use in polymer fuel cells and the optimization of characteristics by experimental test design. For this purpose, the Minitab software is used. Besides, this study was examined the physical, mechanical, and electrical characteristics of the constructed bipolar plates through performing the tests of water absorption, calculation of density, the test bending strength, contact resistance, electrical conductance. The pressure and the curing time were considered as the input parameters of the optimization, and the goal is to optimize the flexural strength and interfacial contact resistance to achieve the U.S Department of Energy's 2020 target for the bipolar plates of polymer fuel cells. The results show that with a pressure of 79.499 MPa and the curing time under pressure was 70s, the parameters of flexural strength and optimum interfacial contact resistance are 53.91 MPa and 10.57 mΩ.cm2, respectively. The properties also include water absorption and electrical conductivity in the through-plane (TP) direction 0.36 percent and 27.22 (S/m) respectively, which is in line with the goals of the US Department of Energy.

Forming limit Curves are one of the common tools to predict the necking in various forming processes. In this Study, the Marciniak-Kuczynski instability theory by applying Gotoh yield function is utilized to estimate the forming limit curves for the AA6016-T4 aluminum sheet in plane stress conditions. Also, the effect of three different hardening models including Swift, Voce, and a linear combination of the Swift and Voce models to determine the limit curves are investigated. The comparison between the theoretical forming limit curves and experimental results from Nakazima test, determines the accuracy of the hardening models in predicting the limit strains. Since in many new forming processes such as hydroforming and incremental sheet forming processes, investigation the process in plane stress state is not exact assumption, Therefore, in continuation of the paper, generalized forming limit curves are plotted based on the developed Marciniak-Kuczynski model by extending the Gotoh yield function, and the effect of compressive normal stress and through-thickness shear stress on forming limits of the sheet are investigated. The results indicated that by applying the compressive normal stress and through-thickness shear stresses, the limit strains increase and the formability is improved, in contrast, the limit stresses move down in the diagram.

Electrochemical finishing is a nontraditional finishing processes by which the surface roughness of the metallic workpiece is reduced due to anodic dissolution. Different parameters like the cathode material, inter electrode gap, chemical composition and concentration of electrolyte and its flow rate and temperature along with the electric potential affect the finishing performance. The important performance parameters are surface roughness, material removal rate, and the dimensional tolerance of the workpiece. In this article the effect of inter electrode gap, cathode geometry, cathode tool feed rate, and electric potential on the process outputs are evaluated experimentally. Due to the high number of input and output variables and possible interactions between the input variables, Box-Behnken design in response surface methodology is selected for designing the experiments. Using this response surface methodology, the effect of input parameters on process outputs and the possible interactions between the input variables are extracted. Also, multi-objective optimization is performed for determining the input variables adequate for maximizing the material removal rate along with achieving a predetermined amounts of surface smoothness and geometric tolerance.

Due to the need for orthopedic surgeries, the mechanical behavior of cortical bone in cyclic loading and physiological strain rate has been investigated. The emphasis is on developing a structural law that can establish the behavior during loading, unloading and reloading observed in experiments. The created models have elastic, damage, and plastic modes. The formulations are based on two variables: internal damage and plastic strain. First, two one-dimensional models independent of the strain rate are formulated, one with one damage variable and the other with two separate damage variables in tension and compression, are examined, and using laboratory data, the coefficients of each model are obtained. By comparing the simulation results and laboratory data, the necessary modifications have been made to the models. Finally, by combining the Bresler-Pister anisotropic yield criterion and the one-dimensional model independent of the rate associated with the two damage variables, the corresponding three-dimensional model was obtained. This three-dimensional model was implemented in the form of an explicit finite element method and the result showed acceptable compatibility with the simulation results of the one-dimensional model and experimental data. This three-dimensional model will be suitable for simulating complex geometries. The coefficient of determination for one-dimensional models RI, ±RI, RI, and ±RI has been modified and the three-dimensional model has obtained values of 0.882174, 0.965665, 0.995508, 0.996279, and 0.984866, respectively

In this paper, by using the Hellinger-Reissner functional, an efficient eight-node plane element with two degrees of freedom in each node is constructed. To do this, two independent displacement and stress fields in the Hellinger-Reissner functional are used. To find the stress field, instead of using hypothetical functions, the analytical solution of the governing differential equation is used. In this method, by solving the governance compatibility equation, the Airy's analytical stress functions are available. Then, by applying these stress functions, the stress field within the element is obtained. Also, for the displacement field of element, the eight-node isoparametric element interpolation functions are used. Next, by minimizing the Hellinger-Reissner mixed functional relative to the independent stress and displacement fields, the stiffness matrix and the nodal force vector are made available. To show the accuracy and efficiency of the proposed element, various benchmark tests will be analyzed. In these tests, the ability of the element for analysis of the curved structures with coarse meshes is evaluated. Also with the help of irregular meshes, the sensitivity of the response to mesh distortion is studied. These tests show the high accuracy of the proposed element in the analysis of complicated problems.