نشریه مهندسی مکانیک ایران
سال بیست و سوم شماره 3 (پیاپی 64، پاییز 1400)

In this study, the effect of nanoparticles addition on the behavior of 12-layer glass/epoxy composite plates, under quasi-static shear loading, was investigated experimentally. In this research, the effect of parameters such as the addition of hydroxide modified carbon nanotubes to the composite structure, three loading speeds of 5, 250 and 500 mm/min and three forms of permeable geometry on quasi-static test results were investigated. The results showed that adding nanoparticles to the composite structure increased the strength, fracture strain and flexibility of the composite, which would allow the penetrant to exit the composite later. Also, as the loading rate increases, the strength of the composite against the permeant increases and as the permeate geometry changes, the fracture mechanism changes.

Making passengers feel comfortable during their commuting and travels can be identified as one of the main goals of the suspension systems in vehicles. This goal can be achieved by reducing the negative impacts of bumps of roads and streets on vehicles and its passengers.The purpose of this paper is to reduce the negative impacts of streets on occupants of cars who pass in speed limited zones in urban routes and consequently enhance their comfort by proposing a new mechanism in field of suspension system of vehicles. To this end, this paper investigates the suspension system control considering the effects of weight of passengers, their sitting position (sitting on rear or front seats of car), speed of vehicle and profile of speed bumps.It will be observed by applying control over the suspension system, comfort of passengers, compared to the uncontrolled state, will be enhanced by 8 to 28 percent.

Nano-indentation test is one of the most common method to study the material post-yielding behavior providing a suitable material model. Nowadays, this test is also used to investigate the pressure-dependent behavior and other mechanical behaviors of bone. Different material models such as Johnson-Cook, von-Mises, Drucker-Prager, and Hill models have been presented to consider the anisotropy, pressure dependency, strain rate, and temperature dependency of cortical bovine bones similar to human bone in tension and compression.In the present study, using the Arbitrary Eulerian-Lagrangian (ALE) finite element method in Abaqus software with appropriate contact conditions, the material flow and the results of bone pile-up was well predicted with an error of less than 1%. Also, suitable parameters of the extended Drucker-Prager model for predicting post-yielding bovine cortical bone behavior were presented such that the force-displacement curve of test, showed less than 5% deviation from the experimental results. The friction angle 46°, and zero-degree dilation angle along with the frictional contact conditions between the tool and the bone with a coefficient of 0.3 provided the best parameters to predict post-yielding behavior. It was also shown that changing the angle of dilation from zero to 10 degrees can increase the maximum force applied to the bone up to 40%.

In the present article, the effects of high-power high-frequency acoustic noise on the dynamical response and fidelity of the sensing signal of the MEMS vibratory gyroscopes are investigated. At first, differential equations of motion the system with four degrees of freedom by considering the frame of the gyroscope are derived and rewritten in state-space form. In these equations, the interaction of the acoustic noise with the gyroscope is modeled as a mechanical force. Then, a Simulink model of the MEMS vibratory gyroscope dynamics is established and the effects of harmonic and random high-power high-frequency acoustic noises on the performance of gyroscope are studied. Influences of different parameters such as harmonic noise frequency, sound pressure level and quality factor of the gyroscope are explored. Numerical simulation results show the proximity of the noise frequency to the resonance of the gyroscope as well as pressure level deteriorate the sensing signal while the quality factor of the system rejects noise effects.

Combination of metal and composites are frequently used in manufacturing structures.Therefore it is a great importance to join these mat ends composite and metals strongly. Thisjoint between metals and composites plays a key role in hybrid designs. Hybrid design is anewly appearing process for joining metals and composites, which have special and demandingproperties, such as higher strength, higher resistance to radiation and compatible design, etc. Inthe present study, which is an experimental investigation of joining metals and composites usingfriction lab joining (FLJ) method the composite is made up glass fibers, polymer PA6 asThermoplastic and 20% weighs glass fiber. Aluminum alloy (AL 5052) is used as metal.The goal of this study is to explore the strength of joint between composite and metal, which ismade using FLJ in two different ways (static and dynamic). During the study, progress rate,spinning speed and depth of penetration are parameters to be considered as effective on the jointstrength. The results showed that the joint properties and strength was affected by all 3mentioned Parameters, in which, when the penetration depth decreases and normal spinningspeed and progress rate increases, the most efficient joint properties (strength) has beenobtained. As pressure and temperature increases in the joining area, GFRTP gets thinner andthe joint becomes weaker. Due to porosity and voids in the joining area the joint can be failed.The strength of joints in specimen showed a good result in fatigue test. In 72% of the fatiguetest the failure occurred in composite itself not in joint between AL5052/GFRTP.

In this paper, stability of a group of networked cascade control systems based on a new continuous-time model is investigated and H∞ state feedback controllers considering H∞ norm bounded constraint are designed in order to attenuate external disturbances. The main objective of this research is to simplify stability analysis and provide the possibility of considering different configurations based on a continuous-time state-space model for these systems.To this aim, here it is assumed that data transformation between the secondary controller and the actuator is performed through a communication network. Using communication networks would result in some imperfections such as communication delay and data packet loss which are considered in the modelling of the system. Then, the state-space equations of the systems are converted to an equivalent augmented state-space equation. Stability of the system is analyzed based on the Lyapunov-Krasovskii theorem and using free weighting matrix method and controller gains as well as maximum allowable delay bound are computed. Simulation results confirm the validity of the proposed method.

The most common types of mechanical arms are robots that are used as palletizing robots to transport light and heavy loads. In robots that are used to move heavy loads, increasing the carrying capacity of the robot while maintaining dexterously, accuracy, repeatability and lightness has always been one of the issues studied by researchers. With this approach, in the present paper, the kinematic design and dimensional optimization of the geometry of a four-degree robotic robotic arm have been performed. The primary geometry is designed using parallel parallelograms to allow horizontal load carrying. After the initial design of the geometry dimensions of the robot, using the finite element method, the geometric optimization of the structure has been done in such a way that changes in the geometric dimensions of the arms as design parameters result in receiving the best results for the objective function. Deformation of the arms and proper distribution of load force among all arms. Using the optimization results of this paper and achieving a set of parametric relationships for the geometry of the robot structure, a shorter path can be taken to design these robots and With optimal geometry, parameters such as not increasing the dimensions of the arm sections to overcome stress and deformation, not increasing the overall weight of the structure, followed by increasing accuracy, repeatability, more load carrying capacity, robot dexterously and not enlarging the overall dimensions of the robot Improve.

The free vibration features of rotating functionally graded microbeams in thermal environmentare presented in this paper. The governing equations are extracted on the basis of the Euler-Bernoulli beam assumptions beside the modified couple stress theory. The finite elementmethod is applied on the weak form of the strain and the kinetic energies to extract the naturalfrequencies and the associated modeshapes. The nonlinear static equations of motion due to therotation and the thermal environment are treated employing the Newton-Raphson technique.Moreover, the natural frequencies are estimated from the linearized equations of motion aboutthe static configuration. After the validation of the present results, the rotation speed, thematerial length scale parameter, the temperature change, the power law exponent and theslenderness ratio impacts on the fundamental natural frequency and the first and the secondmodeshapes are examined. The outcomes indicate the increment of the natural frequency aftera threshold value of the power law exponent depends on a given rotation speed for the rotatingmicrobeams in comparison with the stationary microbeams. Furthermore, the modeshapes ofrotating functionally graded microbeams vary by the power law exponent while for stationaryfunctionally graded microbeams the modeshapes are invariant with respect to the power lawexponent even in the presence of the thermal environment.

In recent years, researches on energy harvesting by piezoelectric ceramics have increased. Generally, linear electromechanical constitutive equations have been utilized to model the behavior of piezoelectric based harvester. But, the linear modeling shows erroneous output for high amplitude and frequency inputs. In these cases, due to nonlinear material behavior, the nonlinear modeling should be carried out. In this paper, the nonlinear behavior and optimum response of a symmetric bimorph cantilever under the base excitation is studied. Electromechanical formulation is based on the Euler-Bernoulli beam theory. A proposed nonlinear enthalpy is used to model the nonlinear dynamic using Lagrange equations. Applying the multiple scale perturbation method, the nonlinear coefficients are identified experimentally (μ ̅_1=3.0090×〖10〗^16 and _1=-4.5804×〖10〗^20 ). Then, nonlinear behavior of harvester has been analyzed considering generated voltage, current and beam deflection. Finally, using the results of Power FRF, the optimum load resistance is achieved to maximize the generated power (R_l=177.828 kΩ).

In this paper, the chaotic dynamic analysis along with chaos controller of an active suspension in vehicle has been studied. The unstable periodic orbits of the system are stabilized using the developed delay feedback control algorithm based on the fuzzy sliding mode system. Firstly, the equations of model are derived via Newton-Euler rules and then, power spectrum density and bifurcation diagrams have been used to confirm chaos in the system. Variations of the control parameters in the bifurcation diagrams demonstrate the changes of system behavior from the periodic to the irregular chaotic responses.Finally, to eliminate the chaos in the vertical dynamics of vehicle, a novel fuzzy sliding delay feedback control algorithm is developed on the active suspension. Using fuzzy logic, the controller gain of the sliding delay feedback control is online estimated that is caused to reject the chattering phenomenon in the sliding mode algorithm beside the improvement of the responses. Simulation results of the control system depict a reduction of settling time and energy consumption along with eliminating the overshoots and chaotic vibrations.