The active buckling control of laminated composite beams with embedded shape memory alloy wires

In this paper, the results of an experimental analysis on the active buckling control behaviour of a laminated composite beam with embedded shape memory alloy (SMA) wires are presented. For the purpose of enhancing the critical buckling load, active buckling control was investigated through the use of the reaction time associated with the shape recovery force of SMA wires. An increased critical buckling load and altered deflection shape due to the effects of activation of embedded SMA wires are represented qualitatively and quantitatively on the load–deflection behaviour records. The results obtained from this active buckling control test confirm that the buckling resistance in a composite beam with embedded SMA wires can be increased by the use of an activation force of the embedded SMA wires. Based on our experimental analysis, a new formula for the behaviour control of active buckling in a laminated composite beam with embedded SMA wires is also suggested.     

Coupled extensional vibrations of longitudinally polarized piezoceramic strips

A system of one-dimensional equations for coupled length-extensional, width-stretch, and symmetric width-shear vibrations of piezoceramic strips polarized in the length direction is derived from the two-dimensional, second-order plate equations by averaging the mechanical displacement and the electrostatic potential over the strip thickness. The boundary conditions correspond to the case of electrically forced vibrations. Theoretical values are compared with results of a previous analytical model and with experimental data.     

Thermal buckling and postbuckling analysis of a laminated composite beam with embedded SMA actuators

In this paper, the thermal buckling and postbuckling behaviours of a composite beam with embedded shape memory alloy (SMA) wires are investigated analytically. For the purpose of enhancing the critical buckling temperature and reducing the lateral deflection for the thermal buckling, the characteristics of thermal buckling are investigated through the use of the shape recovery force associated with SMA wire actuators. The results of both thermal buckling and postbuckling behaviours present quantitatively how the shape recovery force affects the thermal buckling behaviour. The analytical results show that the shape recovery force reduces the thermal expansion of the composite laminated beam, which results in both an increment of the critical buckling temperature and also a reduction of the lateral deflection of postbuckling behaviours. A new formula is also proposed to describe the critical buckling temperature of the laminated composite beam with embedded SMA wire actuators.     

Reducing friction-induced vibration using intelligent active force control (AFC) with piezoelectric actuators

In this paper, a novel approach to reduce the effect of mode coupling that causes friction induced vibration (FIV) is proposed by applying an intelligent active force control (AFC)-based strategy employing piezoelectric actuators with hysteresis effect to a simplified two degree-of-freedom mathematical model of a friction-induced vibration system. At first, the model is simulated and analysed using a closed loop pure Proportional-Integral-Derivative (PID) controller. Later, it is integrated with the intelligent AFC with fuzzy logic (FL) estimator and simulated under similar operating condition. After running several tests with different sets of operating and loading conditions, the results both in time and frequency domains show that the PID controller with the intelligent AFC is much more effective in reducing the vibration, compared to the pure PID controller alone.     

Reliable modeling of piezoceramic materials utilized in sensors and actuators

Piezoceramic materials are widely utilized in actuator and sensor devices. In order to model the behavior of these devices and to reduce their development time, numerical simulation tools are frequently applied. However, the simulation results strongly rely on the material behavior assumed for piezoceramics. Here, we present approaches for reliable modeling of this material behavior which have been developed at the Chair of Sensor Technology (Friedrich-Alexander-University Erlangen-Nuremberg) in recent years. Both the small signal behavior and the large signal behavior of piezoceramic materials are discussed. For the identification of material parameters required within the small signal model, we apply a mathematical Inverse Method. The large signal behavior of piezoceramics is described by means of a phenomenological approach that is based on the so-called Preisach hysteresis operator. As the presented results for different piezoceramics clearly show, the utilized modeling approaches lead to reliable simulation results and can, therefore, be applied to predict the behavior of piezoceramic materials.     

Shape control of smart composite plate with non-rectangular piezoelectric actuators

Quasi-static shape control of a smart structure may be achieved through optimizing the applied electric fields, loci, shapes and sizes of piezoelectric actuators attached to the structure. In this paper, a finite element analysis (FEA) software has been developed for analyzing static deformation of smart composite plate structures with non-rectangular shaped PZT patches as actuators. The mechanical deformation of the smart composite plate is modeled using a 3rd order plate theory, while the electric field is simulated based on a layer-wise theory. The finite element formulation is verified by comparing with experimentally measured deformation. Numerical results are obtained for the optimum values of the electric field in the PZT actuators to achieve the desired shape using the linear least square (LLS) method. The numerical results demonstrate the influence of the shapes of actuators.     

A comparison of buckling and postbuckling behavior of FGM plates with piezoelectric fiber reinforced composite actuators

Compressive postbuckling under thermal environments and thermal postbuckling due to a uniform temperature rise are presented for a simply supported, shear deformable functionally graded plate with piezoelectric fiber reinforced composite (PFRC) actuators. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM and PFRC layers are assumed to be temperature-dependent. The governing equations are based on a higher order shear deformation plate theory that includes thermo-piezoelectric effects. The initial geometric imperfection of the plate is taken into account. A two step perturbation technique is employed to determine buckling loads (temperature) and postbuckling equilibrium paths. The numerical illustrations concern the compressive and thermal postbuckling behaviors of perfect and imperfect, geometrically mid-plane symmetric FGM plates with fully covered or embedded PFRC actuators under different sets of thermal and electric loading conditions. The results for monolithic piezoelectric actuator, which is a special case in the present study, are compared with those of PFRC actuators. The results reveal that, in the compressive buckling case, the applied voltage usually has a small effect on the postbuckling load–deflection curves of the plate with PFRC actuators, whereas in the thermal buckling case, the effect of applied voltage is more pronounced for the plate with PFRC actuators, compared to the results of the same plate with monolithic piezoelectric actuators.     

Closed form solutions for buckling and postbuckling analysis of imperfect laminated composite plates with piezoelectric actuators

Buckling and postbuckling behavior of symmetric laminated composite plates with surface mounted and embedded piezoelectric actuators subjected to mechanical, thermal, electrical, and combined loads is studied. Formulation is based on the classical laminated plate theory with von-Karman non-linear kinematic relations. Initial geometrical imperfections are also accounted, and finally applying Galerkin procedure, the resulting equations are solved to obtain closed form expressions for non-linear equilibrium paths. Temperature dependency of thermo-mechanical properties is considered. Three cases of simply supported boundary conditions are investigated. Effects of in-plane compressive loading, temperature dependency and independency of properties, electrical loading, lay-up configuration, and geometric imperfection are discussed. Results for various states are verified with the known data in the literature.     

Piezoelectric actuators and sensors location for active control offlexible structures

A method for optimal positioning of piezoelectric actuators and sensors on a flexible structure is presented. First, a two-dimensional (2-D) model of a piezoelectric actuator bonded to a plate is obtained. Then, a Ritz formulation is used to find a state model of the system in view of its control. To define an optimal positioning strategy, an energy based approach is developed. This leads quite naturally to the study of controllability and observability properties of the overall dynamical model. A new criterion based on energy assessment is proposed to locate actuators and sensors     

Genetic algorithm based optimal design for vibration control of composite shell structures using piezoelectric sensors and actuators

The present article deals with the design of optimal vibration control of smart fiber reinforced polymer (FRP) composite shell structures using genetic algorithm (GA) based linear quadratic regulator (LQR) and layered shell coupled electro-mechanical finite element analysis. Open loop procedure has been used for optimal placement of actuators considering the control spillover of the higher modes to prevent closed loop instability. An improved real coded GA based LQR control scheme has been developed for designing an optimal controller in order to maximize the closed loop damping ratio while keeping actuators voltages within limit. Results show that increased closed loop-damping has been achieved with a large reduction of control effort considering control spillover.     

Transient analysis and control of delaminated composite plates in hygrothermal environment using active fiber composite actuator

Abstract

In the present article, the transient analysis and control of delaminated composite plates under hazardous environmental conditions using active fiber composite (AFC) is discussed. Top and bottom layers of the laminated composite plate are embedded AFC layers. The present investigation utilizes AFC as an actuator and sensor. A finite element model for centrally located delamination is developed and coded in Matlab. The proportional controller is used to control the undesirable response in real time. The transient response of the smart delaminated plate is studied for different temperatures and moisture conditions. The feedback control of the dynamic response is performed with the help of velocity and displacement feedback gain to the AFC actuator. The key observations from the numerical studies are; the dynamic response and the frequency response of composite plate increase due to delamination and also with the increase of the temperature and moisture concentrations. The response reduces when the feedback control loop is activated. So, the overall performance of the delaminated plate structure in hygrothermal environment may be enhanced.     

Sensing and control of flow separation using plasma actuators

Single dielectric barrier discharge plasma actuators have been used to control flow separation in a large number of applications. An often used configuration involves spanwise-oriented asymmetric electrodes that are arranged to induce a tangential wall jet in the mean flow direction. For the best effect, the plasma actuator is placed just upstream of where the flow separation will occur. This approach is generally more effective when the plasma actuator is periodically pulsed at a frequency that scales with the streamwise length of the separation zone and the free-stream velocity. The optimum frequency produces two coherent spanwise vortices within the separation zone. It has been recently shown that this periodic pulsing of the plasma actuator could be sensed by a surface pressure sensor only when the boundary layer was about to separate, and therefore could provide a flow separation indicator that could be used for feedback control. The paper demonstrates this approach on an aerofoil that is slowly increasing its angle of attack, and on a sinusoidally pitching aerofoil undergoing dynamic stall. Short-time spectral analysis of time series from a static pressure sensor on the aerofoil is used to determine the separation state that ranges from attached, to imminent separation, to fully separated. A feedback control approach is then proposed, and demonstrated on the aerofoil with the slow angle of attack motion.     

Dynamic buckling of an elastoplastic column

Dynamic buckling of columns under axial step loading which produces plastic behaviour is investigated. An experimental study is described and an elastoplastic model is developed in order to analyse the buckling process. Good agreement is obtained between the theoretical predictions and experimental results which justifies the main assumptions underlying the model.     

Edge-wave buckling of rolled elastic strips: asymptotic results

The problem considered in this paper concerns the edge-wave buckling phenomenon commonly encountered in forming processes such as rolling and levelling. Due to the combined action of global tensile forces and residual stresses, the elastic strips involved in these scenarios experience a symmetric short-wave deformation pattern that tends to be confined near their long edges. We use boundary-layer techniques to provide simple estimates for the critical load and the wavelength of the buckling waves. A number of complementary asymptotic features of the marginal stability curves are also reported.     

柔性板压电作动器的优化位置与主动控制实验研究

对柔性悬臂板主动控制中作动器的优化位置进行研究,其中作动器采用压电形式,优化算法采用粒子群方法,指标函数采用基于能量的可控Gramian优化配置准则。仿真和实验结果显示,粒子群优化算法能够有效地对作动器的优化位置进行计算,尤其适用于多个作动器的位置优化问题,基于作动器最优位置的控制设计能够取得良好的控制效果。     

Optimum buckling design of composite stiffened panels using ant colony algorithm

Optimal design of laminated composite stiffened panels of symmetric and balanced layup with different number of T-shape stiffeners is investigated and presented. The stiffened panels are simply supported and subjected to uniform biaxial compressive load. In the optimization for the maximum buckling load without weight penalty, the panel skin and the stiffened laminate stacking sequence, thickness and the height of the stiffeners are chosen as design variables. The optimization is carried out by applying an ant colony algorithm (ACA) with the ply contiguous constraint taken into account. The finite strip method is employed in the buckling analysis of the stiffened panels. The results shows that the buckling load increases dramatically with the number of stiffeners at first, and then has only a small improvement after the number of stiffeners reaches a certain value. An optimal layup of the skin and stiffener laminate has also been obtained by using the ACA. The methods presented in this paper should be applicable to the design of stiffened composite panels in similar loading conditions.     

Post‐buckling optimization of composite structures using Koiter's method

Thin‐walled structures, when compressed, are prone to buckling. To fully utilize the capabilities of such structures, the post‐buckling response should be considered and optimized in the design process. This work presents a novel method for gradient‐based design optimization of the post‐buckling performance of structures. The post‐buckling analysis is based on Koiter's asymptotic method. To perform gradient‐based optimization, the design sensitivities of the Koiter factors are derived, and new design optimization formulations based on the Koiter factors are presented. The proposed optimization formulations are demonstrated on a composite square plate and a curved panel where the post‐buckling stability is optimized. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamic bifurcation buckling of an impacted column

In this paper, the dynamic counterpart of the celebrated Euler buckling problem is formulated and solved by considering the case of a slender column that is impacted by a falling mass. We introduce a new notion, that of the time to buckle, “t^∗”, which is the corresponding critical quantity analogous to the critical load in static Euler buckling. A set of experimental results previously presented by Gladden et al. [J.R. Gladden, N.Z. Handzy, A. Belmonte, E. Villermaux, Dynamic buckling and fragmentation in brittle rods, Physical Review Letters 94 (3) (2005) 035503], are used to illustrate the notions we introduce and as a means for comparison against the predictions of our work.