جستجوی مقالات مرتبط با کلیدواژه "shape memory alloy" در نشریات گروه "مکانیک"

Shape memory alloys (SMAs) are a special kind of smart materials with an intrinsic shape memory effect. This characteristic brings up SMAs as an actuator in dynamical mechanisms. These materials can recover their initial length under special thermal operations. This paper deals with fuzzy-PID control of contrary mechanisms actuating with a pair of SMA wires. The Brinson model combining with the Elahinia’s conditions are employed to describe the phase transformation models. By combining the Newton second law, transformation models, heat transfer and strain relations, the governing equations of the contrary mechanism is derived. Due to nonlinear behavior of SMA actuators, the non-model-based controllers are preferred compared with the model-based ones. Therefore, the fuzzy-PID control method is employed to control the position of the closed-loop system. The fuzzy rules are defined such that the coefficients of the PID controller are tuned according to the system response. Both numerical and experimental results are provided to illustrate the effectiveness of the proposed approach. It will be shown that under the proposed method, the tracking error will converge to zero asymptotically.

This article aims at studying the free and forced vibrations of shape memory alloy beam ‎actuators. The constitutive equations are derived based on a three dimensional ‎phenomenological model which accounts for pseudoelastically and shape memory effect by ‎considering phase transformation strains in the formulation. In the present study, the ‎pseudoelastic deformations are studied. Assuming Timoshenko beam model for the structures ‎with moderate thickness, equations of motion are derived through Hamilton principle, and the ‎obtained partial differential equations are discretized by applying the Generalized Differential ‎Quadrature approach and then are solved incrementally using Newmark integration method. ‎The return mapping algorithm, considering Newton-Raphson iteration procedure, is employed ‎to update phase transformation strains and any related parameters during solution in each time ‎steps. Results show that energy dissipation occurs due to hysteric behavior of SMA beams ‎during vibrations for both free and forced cases. In most cases, the reduction in amplitudes ‎continues till the material behaves like the elastic solids within austenite phase where no ‎dissipation is appeared. Also, it can be observed from the results that the amplitude of ‎damped vibrations is constant for SMA structure. Therefore, it exhibits more stable behavior ‎in comparison with elastic beam with similar harmonic actuations. Consequently, it is ‎concluded that the SMA materials can be applicable to adjust response frequency in addition ‎to their various applications such as in dampers.

In this study, the forced vibrations of an annular circular plate with clamped edges under harmonic load is investigated. Analysis of circular plate is based on First-order Shear Deformation Theory (FSDT). The pseudoelastic behavior is simulated by Boyd-Lagoudas constitutive model. The Hamilton’s principle is used to obtain the equations of motion.In the state without phase change (pure austenite) the plate was examined in nonlinear conditions and compared with the existing reference.Differential Quadrature, Newmark methods, and convex cutting plane mapping algorithm are utilized to get the time and frequency responses of the plate. The phase transformation effects are studied on the time and frequency responses of the plate. Also, the harmonic load and the harmonic load, with a constant value are investigated. Then, the accuracy of these results is checked with the available literature and FEM software ABAQUS. The results indicate that the alloy phase transformation leads to reduced material strength and the nonlinear behavior of the alloy.

Thermal motors are used to generate mechanical energy using heated water produced by different equipment, without environmental pollutions. In this paper, a thermal engine is first designed and manufactured using Nitinol wires. Then, the effects of different parameters on angular velocity, output torque and engine rotation time are investigated. The results show that increasing hot-water temperature and decreasing cold-water temperature increase the angular velocity. However, as long as transformations get completed, these parameters have a neglectable effect on the torque. In addition, increasing the wires’ diameter and number and using the friction-reducer beads, increase the output torque and angular velocity. It is also observed that decreasing the transformation temperature increases the duration of rotation and angular velocity of the engine. The maximum angular velocity is related to a certain position of the fixed constraints. The maximum torque and angular velocity are calculated to be about 20.601 N.mm and 58 rpm respectively.

One of the common methods to resolve artery stenosis is the insertion of a shape memory alloy stent in the artery. The use of shape memory alloys in the manufacturing of self-expandable stent has expanded because of the superelastic behavior of this alloy. In this paper, we simulated a shape memory alloy stent insertion in an artery to explore stress and damage effects arising from the stent insertion on the artery by using ABAQUS software. To simulate the mechanical behavior of artery, we considered the effect of the inelastic arterial properties (stress softening and recoverable inelastic deformation) that activated under supraphysiological loading in the stenting process, and to simulate stent behavior, the Souza model is used. These two models were applied in ABAQUS by UMAT codes. By using the damage model, the amount of damage in the artery, which is one of the factors of restenosis, is investigated. Also, in this paper, we have used real diseased artery geometry, which was specified from high-resolution magnetic resonance images, therefore the analysis is more in line with reality and it is possible to determine the location of the maximum stress and damage in the artery.

In this paper, the effect of shape memory alloy on low-velocity impact response of rectangular sandwich plates with composite facesheets and soft auxetic cores is investigated using a new higher-order global–local hyperbolic plate theory. In order to obtain accurate results with the least error, non-uniform and time-dependent distribution for the phases of SMA and the transverse compliance of the soft core are considered. Also, a refined contact law is proposed instead of using the traditional Hertz law and different contact laws are considered for the loading and unloading phases. Stiffness effects of all layers along with the effect of plate thickness on contact stiffness are considered. The obtained nonlinear finite element governing equations are solved by making use of an iterative algorithm at each time step. The results of the present study are compared with the experimental results in other references, and it is proved that the results are valid. Finally, the effect of auxetic core, core Poisson's ratio, SMA wires, and indenter energy on impact response of composite sandwich plat are investigated. The results show that the auxetic core increases the apparent stiffness of the contact area that causes an increase in impact forces and a decrease in the lateral deflection and impact duration. Besides, the SMA can absorb a remarkable portion of the stored impact-induced strain energy due to the superelastic and hysteretic natures of the SMA material, which results in increasing impact strength of the sandwich plate and decreasing the damage caused due to the impact.

Shape Memory Alloy (SMA) wires are currently employed in robotics as actuators of prosthetic limbs and medical equipment due to advantages such as reducing the size in the application, high power-to-weight ratio and elimination of complex transmission systems. In this paper, a fuzzy control system has been designed and implemented for an artificial finger using the SMA actuators. This robotic finger has been designed and modeled with three revolute joints and three SMA wires as the tendon in order to adduction each phalange of the finger and torsional springs to restore them to their original positions. The dynamic model of the finger has been simulated in MATLAB/Simulation. Based on the simulation results, optimal choice of parameters and system features has been obtained and a prototype of finger has been built and tested. Gains of the controllers are set so that the current applied to SMA wires has minimum overshoot and the output of the system has minimal time to achieve stability. The comparison between the simulation results and the actual measured data show that the simulated model is accurate.

Shape memory alloys (SMAs) are suitable candidates in various fields of engineering. One advantage of these alloys is their capabilities in developing high strain and force. In addition to these great features, lightweight and super-elastic behavior are other traits of these materials. These specifications are of such an importance that make SMAs to be suitably used in further engineering applications. However, their intrinsic hysteresis non-linear behavior make their usage as position actuators difficult. Despite this challenge, there are various methods proposed in the literatures to model the hysteresis behavior of such materials. In this paper, a generalized Prandtl- Ishlinskii model, because of its simplicity, efficiency and inverse analytical capability, has been used for modeling the SMA behavior. In addition, the hysteresis modeling has been validated via experimental data of one of the articles. In the control section, however, two control systems consisting PID and fuzzy sliding mode controllers have been used. Fuzzy sliding mode control system is a method that can be used in systems without mathematical model and leads to increase in their robustness. It is shown in this paper that by using this method, it is possible to apply a suitable control input to the system in order to vanish the error signal. However, by using PID controllers, the error signal is not acceptable due to the constant controller coefficients. The results indicate the more efficient performance of fuzzy sliding mode controller with respect to the classical PID controller.

In this paper, at first a Shape Memory Alloy (SMA) actuator is modeled by Brinson model. Due to high efficiency of Brinson model in modeling SMA behavior, this model is studied in detail in all regions of temperature-stress plane. Then, an SMA actuator, that is composed of a SMA wire connected to a linear spring, is modeled. Since in many SMA actuators, some parameters, like spring stiffness in this case, cannot precisely determined or it is changed by the environment situations, an Extended Kalman Filter (EKF) is used to estimate these parameters. In this filter, an initial guess and its error covariance must be determined. But since this error covariance can’t be determined precisely, the effect of initial error covariance inaccuracy on the parameter estimation is analyzed. Also, since in actual cases the spring may have nonlinear behavior, a simulation is performed by using a nonlinear spring while the estimation is carried out by using linear spring model. These analyses show that EKF can estimate parameters of an SMA-actuated actuator quickly as well as accurately. Also these estimations are robust against the model and initial guess uncertainty.

The scope of the current investigation incorporates the entire process involved in design and development of a Shape Memory Alloy (SMA) actuated wing intended to fulfill morphing missions. At the design step, a two Degree-of-Freedom (DOF) mechanism is designed that is appropriate for morphing wing applications. The mechanism is developed in such a way that it can undergo different two DOF, i.e. gull and sweep, so that the wing can have maneuvers that are more efficient. Smart materials commonly are selected as the actuators due to their suitable thermo-mechanical characteristics. Shape Memory Alloy (SMA) actuators are capable of providing more efficient mechanisms in comparison to the conventional actuators due to their large force/stroke generation, smaller size with high capabilities in limited spaces, and lower weight. As SMA wires have nonlinear hysteresis behavior, their modeling should be implemented in a meticulous way. In this work, after proposing a two DOF morphing wing, an aerodynamic analysis of the whole wing for unmorphed and morphed wings is presented. The results show that the performance of the morphed wing in special flight regimes is improved.

General thermo-mechanical behavior of composites reinforced by shape memory alloy fibers is predicted using a three-dimensional analytical micromechanical method to consider the effect of fibers activation. Composite due to the micromechanical method can be exposed to general normal and shear mechanical and thermal loading which cause to activate the shape memory alloy fibers within polymeric matrix finally. Considering the capabilities of the presented micromechanical model; the fibers arrangement within the matrix is simulated as square distribution. Representative volume element of the composite system consists of two-phases including shape memory alloys fibers and polymeric matrix which is exposed to axial cyclic mechanical loading. In order to display the effect of fiber activation on the overall response of composite, the behavior of polymeric matrix is assumed elastic and shape memory alloy fibers is considered nonlinear inelastic based on 3-D Lagoudas model is simulated. The model is capable to predict the phase transformation and super elastic behavior of shape memory alloys. In order to develop thermo-mechanical equations of the shape memory alloy in the unit cell model, Newton-Raphson nonlinear numerical solution method is used. In the results, the effects of significant parameters on the thermo-mechanical response of composites are investigated and then the composite thermo-mechanical response is demonstrated in the high and low temperature interval and the effect of shape memory alloy wire activation in the composite is addressed. The presented results show that the composite residual strain in mechanical unloading decreases by enhancing temperature. Therefore, the composite residual strain approaches to zero when the temperature is higher than at which austenite transformation finishes. Comparison between the present research results with available previous researches shows good agreement.