نشریه مکانیک مواد پیشرفته و هوشمند
پیاپی 2 (زمستان 1400)

In recent years, with the increasing growth of various industries, the development of advanced industrial structures has been widely increased in many industries such as aerospace, turbines, reactors, and other rotary machines. One of the most applicable rotating structures in this type is rotating drum in air turbine engines, which is very important due to the thermo-mechanical loads applied on it. The drum is a rotary structure that in recent years has been widely used in various sectors such as aerospace industries and nuclear facilities and has a very similar geometry to a thick-walled circular cylinder. This structure is under thermo-mechanical loads. Analysis of rotating drum stresses and investigating effective parameters including loadings at inner and outer radius, rotating speed, and using advanced materials like FGMs instead of homogenous materials is very important in the design of air turbine engine drums. A bunch of useful materials are FGM materials with a non-homogeneous coefficient which is suitable for redesigning a drum with lower stresses and higher safety factor. FGM materials are special types of composites and their properties can change steady and slowly in one or more arbitrary directions. These materials have high mechanical strength at high temperatures against applied loads, which makes them an appropriate selection in the above activity. In this paper, analyzing a rotary drum and investigation on effective parameters including rotating speed, types of loading carrying on internal and external surfaces, thickness, and type of material has been studied. In order to investigate the drum, a thermoelastic analytical solution is performed for both homogenous and FGM states under internal and external loading conditions. The material properties are assumed to vary nonlinearly in the radial direction and the Poisson’s ratio is assumed constant. At first, differential equation of motion for FGM material is derived by assuming the properties functions exponentially and thermal gradients as an arbitrary function of radius. Then the equation is solved analytically using MATLAB engineering software. Stresses and displacements were calculated in clamp-clamp ends boundary conditions. Then, the governing thermal differential equation of the drum was solved and the response was replaced with an arbitrary thermal function considered at first stage of the analysis. After calculating the displacements and stresses applied to drum for FGM and homogeneous states, a study on effective parameters was carried out. changes in the values of different parameters affecting the stresses and displacements, including rotation speed, magnitude, and type of loading on internal and external surfaces in the same working conditions on homogenous and FGM with non- homogeneous coefficients have been investigated. Results clearly show the significant effects of loading conditions, drum rotating speed, and materials deployed to improve the drum behavior. To apply drum’s thermal distribution, the heat transfer function in steady-state conditions has been used. After calculating the displacement and stresses, the effect of various parameters which affect stresses and displacements, including rotating speed, types of loading carrying on internal and external surfaces, thickness, and type of material (non-homogeneous constants) have been investigated. Also, the equivalent stress was obtained using Von Mises criteria. The results show that changing the values of noted affecting parameters has significant affection on stresses and displacements reduction and changing type of radial loadings, rotating speed, thickness and choosing FGM material with appropriate FG coefficients instead of homogeneous state can lead to design a drum with lower stresses and consequently higher safety factor.

In the current paper, the piezoelectric energy harvesting of inhomogeneous beams based on modified beam models is studied. Different classical boundary conditions, which are combination of free, simply and clamped, are contemplated for the structure. The beam mechanical properties are assumed to vary based on the power law along the thickness direction in which volume fractions of the ceramic and metal part can be adjusted using FG parameter. Here, various beam theories such as Euler-Bernoulli, exponential, trigonometric, hyperbolic and fifth-order are modelled using a unified formulation. These beam theories are capable of catching rotary inertia effects and transverse shear deformations. The vibrational performance of the beam is affected by the harmonic vibrations of the base. Additionally, two different dampings including structural damping and viscous damping are modelled in the current formulation. Transverse deflection of the beam is obtained using modal expansion and then electrical power, current and voltage outputs are calculated. Ultimately, in the discussion section, the impacts of different parameters on the vibration and energy harvesting of the beam are analyzed.

Nanoparticle manipulation is a process in which particles are moved on a micro/ nanoscale scale using an atomic force microscope and has a wide range of applications from component production to the medical world. In this study, using the theories of contact mechanics of Hertz, JKR, DMT and BSP, as well as using the structure of the DNA biological cell using the Elman method using ABAQUS software to study the amount of displacement, acceleration, force, stress and velocity in time The DNA molecule is discussed on a base sheet and the factors that affect them. The results show that in the deformation between the target particles and the spherical tip of the needle, the Hertz model showed the least and the JKR model showed the highest deformation and penetration depth. By increasing the angle of the needle tip with the z-axis, the amount of penetration depth and deformation created between the particle and the base plate is reduced. Also, the graph of changes in each of the studied parameters of the effective factors per 20 μm of displacement and 20 milliseconds of time for the DNA manipulation process has been calculated.

Transmitted vibration to driver body (whole-body vibration) in heavy-duty Off-road vehicles without primary suspension leads to health problems in long term such as spine disorder, back pain, heart abnormal beating, vision disable, digestive problem, etc. Commonly, secondary seat suspension is used to isolate vibration and remove health problems, s especially in the spinal column. Passive seat suspension is widely employed for this purpose, but its efficiency is low. Active seat suspension and semi-active suspensions have better performance in blocking unwanted oscillation. Recently, semi-active magnetorheological dampers are focused on by researchers which can adjust their viscosity by electromagnetic flux. It is called smart fluid due to having controllable parameters such as damping ratio by electricity variations. Thus, suspension can dampen oscillation by low electricity current efficiently. The current paper introduces a novel active force control (AFC) equipped with an iterative learning estimator for seat suspension via MR damper. Results of simulations show that it can cancel vibration perfectly. The suspension was coupled to the human body vibration model, and the driver vibration results have been obtained. It is important to note that active force control can also be used to eliminate high-velocity disturbances. Since the vibrations that occur in the car have a high rate of change, the results indicated that active force control equipped with an iterative learning estimator system can be effective in reducing the transmission vibration to the driver so that the first and second vibration peaks was reduced by about 60%.MethodologyAt the first, a dynamic model of an off-road vehicle seat suspension which is equipped with an MR damper has been developed. After that, a PID controller has been designed for semi-active seat suspension. Next, the PID controller has been integrated into the AFC method. Lastly, utilizing the ILA in mass estimation for the AFC approach and simulation results of that has been discussed.The simulation work has been developed employing MATLAB/Simulink software whereas passive suspension and semi-active suspension via the PID and AFCAIL controllers were simulated. To evaluate the performance of the control schemes, the seat suspension model was exposed to a number of various disturbances as road roughness listed as follows:Results and DiscussionIn this section, a comparison between passive suspension and all the control methods has been performed in time and frequency domains. ConclusionA novel controller called the active force control has been employed for vibration control of seat suspension equipped by a magnetorheological (MR) damper. The AFC method was integrated into the iterative learning algorithm to calculate the estimated mass of the system named AFC-IL . The designed controllers were simulated for the vibration canceling of an off-road vehicle seat suspension system. The AFC technique achieved to be uncomplicated in terms of calculation and change it suitable for real-time working conditions. Moreover, the AFC demonstrates high performance and produce robust and accurate response still in the presence of various disturbances. The simulation results express that for known parameters and situations, the proposed AFC-IL method efficiency enhanced in comparison to the popular PID controller. The results exemplify that the AFC-based scheme as an intelligent control technique has proper potential to eliminate the disturbances superiorly for the off-road vehicle seat suspension. Although complementary efforts should be accomplished to investigate the influences of other types of disturbances, parameters and uncertainties changes in real situations such as road trials. In continuing a test rig will be developed to evaluate the AFC scheme performance in real conditions in terms of the vibration attenuating and optimized parameters.

Nowadays, micro/nano materials are widely used in various engineering applications such as nanoelectro- mechanical systems, opto-electronics, nuclear engineering, aerospace engineering, energy storage, civil engineering and etc. recently, different non-classical theories such as the couple stress, the nonlocal elasticity and the strain gradient elasticity theories have been developed to consider the size dependency behavior of the structures in small-scales. In this paper, out of plane vibration analysis of single-walled carbon nanotubes were studied using stress gradient theory, strain gradient theory and the classical theory of elasticity based on the assumptions of the Donnell's thin shell theory.. To determining the free vibration parameters of the carbon nanotube, the kinetic and strain (potential) energies were obtained and will be maximized then using Rayleigh's method the natural frequency was obtained. Natural frequency of the Rayleigh and Love modes of out of plane vibration of the single wall carbon nanotubes out are estimated using stress gradient theory, strain gradient theory and the classical theory of elasticity based on the assumptions of the Donnell's thin shell theory. In order to verify the accuracy and reliability of the present study, the results were obtained in this study were compared and validated with available data in the literature. Using numerical data provided, effect of different parameters including length, thickness and radius of the single-walled carbon nanotubes on the natural frequency of the Rayleigh and Love modes are examined and discussed in detail.

Today, the drilling process is one of the most fundamental machining processes among industrial processes. The drilling process is expanding to high-speed, high-precision machining due to productivity improvements. The drill bits used in this process play an important role and can increase the surface quality and improve the surface roughness. It should be noted that the costs of breaking the drill bit are high. In the micro-drilling process, increasing the rotational speed decreases the machining time, but also causes a faster tool wear rate. Also, reducing the feed rate improves the surface quality, but on the other hand, reduces the material removal rate. Therefore, an accurate selection of various parameters in micro-drilling is necessary to achieve the desired surface roughness. In this paper, firstly, by performing experimental tests, a second-order linear regression mathematical model is presented to predict the surface roughness during micro-drilling operations of brass by input parameters of rotational speed, feed rate, and tool diameter and their effective interactions. Then, using the E-Fast statistical sensitivity analysis method, the effect of the studied parameters on the surface roughness is obtained. The results obtained from the e-Fast statistical sensitivity analysis method show that among the three input parameters, the feed rate with 62% effect on surface roughness as the most important parameter, the rotational speed with 34% effect as the second parameter affecting roughness. The final surface, as well as the tool diameter with only 4% impact, is known as the least effective parameter on the surface roughness in the micro-drilling process of brass micro-drilling.Today, the drilling process is one of the most fundamental machining processes among industrial processes. The drilling process is expanding to high-speed, high-precision machining due to productivity improvements. The drill bits used in this process play an important role and can increase the surface quality and improve the surface roughness. It should be noted that the costs of breaking the drill bit are high. In the micro-drilling process, increasing the rotational speed decreases the machining time, but also causes a faster tool wear rate. Also, reducing the feed rate improves the surface quality, but on the other hand, reduces the material removal rate. Therefore, an accurate selection of various parameters in micro-drilling is necessary to achieve the desired surface roughness. In this paper, firstly, by performing experimental tests, a second-order linear regression mathematical model is presented to predict the surface roughness during micro-drilling operations of brass by input parameters of rotational speed, feed rate, and tool diameter and their effective interactions. Then, using the E-Fast statistical sensitivity analysis method, the effect of the studied parameters on the surface roughness is obtained. The results obtained from the e-Fast statistical sensitivity analysis method show that among the three input parameters, the feed rate with 62% effect on surface roughness as the most important parameter, the rotational speed with 34% effect as the second parameter affecting roughness. The final surface, as well as the tool diameter with only 4% impact, is known as the least effective parameter on the surface roughness in the micro-drilling process of brass micro-drilling.

In this paper, exact close form solution for out of plane free flexural vibration of moderately thick rectangular nano-plates are presented based on nonlocal sinusoidal shear deformation theory, with assumptions of the Levy's type boundary conditions, for the first time. The aim of this study is to evaluate the effect of small-scale parameters on the frequency parameters of the moderately thick rectangular nano-plates. To describe the effects of small-scale parameters on vibrations of rectangular nanoplates, the Eringen theory is used. the Levy's type boundary conditions is a combination of six different boundary conditions; specifically, two opposite edges are simply supported and any of the other two edges can be simply supported, clamped or free. Governing equations of motion and boundary conditions of the plate are derived by using the Hamilton’s principle. The present analytical solution can be obtained with any required accuracy and can be used as benchmark. Numerical results are presented to illustrate the effectiveness of the proposed method compared to other methods reported in the literature. Finally, the effect of boundary conditions, aspect ratios, small scale parameter and thickness ratios on nondimensional natural frequency parameters and frequency ratios are examined and discussed in detail.