Jeng-Jong Ro

Thermal post-buckling and aeroelastic behaviour of shape memory alloy reinforced plates

A novel concept is proposed: the use of shape memory alloy (SMA) to reduce panel thermal deflection and flutter responses. SMA has a unique ability to recover large pre-strains completely when the alloy is heated above the austenite finish temperature Af. The transformation austenite start temperature As for nitinol can be anywhere between -60 °F (-50 °C) and +340 °F (+170 °C) by varying the nickel content. During the recovery process, a large tensile recovery stress occurs if the SMA is restrained. The shape memory effect phenomenon is attributed to a change in crystal structure known as a reversible austenite to martensite phase transformation. This solid-solid phase transformation also gives a large increase in Youngs modulus and yield stress. In this paper, a panel subject to the combined aerodynamic and thermal loading is investigated. A nonlinear finite element model based on the von Karman strain-displacement relation is utilized to study the effectiveness of an SMA-embedded panel on the flutter boundary, critical buckling temperature, post-buckling deflection and free vibration. The study is performed on an isotropic panel with embedded SMA. The aerodynamic model is based on the first-order quasi-steady piston theory. The dynamic pressure effect on the buckling and post-buckling behaviour of the panel is investigated by introducing the aerodynamic stiffness term, which changes the critical buckling temperature. Panels with SMA embedded in either the longer or shorter direction and either fully or partially embedded are investigated for post-buckling behaviour. Similarly, the influence of temperature elevation on the flutter boundary and vibration frequencies is investigated.

Control of sound radiation from a plate into an acoustic cavity using active piezoelectric-damping composites

Sound radiation from a plate into an acoustic cavity is controlled using patches of active piezoelectric-damping composites (APDC). The APDC under consideration consists of piezoelectric fibers embedded across the thickness of a visco-elastic matrix in order to control the compressional damping characteristics of the composite. The effectiveness of the APDC treatments in attenuating the sound radiation from thin plates into cavities is demonstrated theoretically and experimentally. A finite element model (FEM) is developed in order to describe the dynamic interaction between the plate, the APDC patches and the acoustic cavity. The FEM is used to predict the dynamics of the plate/acoustic cavity and the sound pressure distribution for different control strategies. The predictions of the FEM are validated experimentally using a square aluminum plate whose sides are 29.8 cm long and have a thickness of 0.04 cm. The plate is mounted on a cavity. The test plate is treated with a single APDC patch placed at the plate center. The patch is and is made of 15-25% lead zirconate titanate (PZT) fibers embedded in soft and hard polymeric resin matrices and provided with silver-epoxy electrodes. Vibration and sound pressure level attenuations of about 70% are obtained, at the plate/cavity first mode of vibration, with a maximum control voltage of 330 V using a derivative feedback controller. Such attenuations are attributed to the effectiveness of the APDC treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping (PCLD) treatments. Comparisons between the theoretical predictions of the FEM and the experimental results indicate close agreement between theory and experiments. The obtained results suggest the potential of the APDC treatments in controlling the sound radiation from plates into acoustic cavities. Such potential can be exploited in many critical applications such as cabins of aircrafts and automobiles to ensure a quiet environment for the occupants.

Control of sound radiation from a plate into an acoustic cavity using active constrained layer damping

The sound radiation from a vibrating flat plate coupled with an acoustic cavity is controlled using a single patch of active constrained layer damping (ACLD), active control (AC) and passive constrained layer damping (PCLD) treatments. Dynamic and acoustic finite element models are developed to study the fundamental phenomena governing the coupling between the dynamics of the ACLD and AC/PCLD treated plates and the acoustic cavities. The models are used to compute the frequencies, mode shapes and sound radiation for different damping configurations and control gains. The damping characteristics of the ACLD/plate system are compared with those of plates with AC/PCLD treatments. Such comparisons are essential in quantifying the individual contribution of the active and passive components to the overall damping characteristics, when each operates separately and when both are combined to interact in unison as in the ACLD treatments. The predictions of the models are validated experimentally using a square aluminum plate, whose sides are 29.8 cm and thickness is 0.04 cm, mounted on a 29.8 cm × 29.8 cm × 75 cm cavity. The plate is treated with an ACLD treatment bonded to one side and an AC treatment placed on the other side. The ACLD treatment consists of a visco-elastic damping layer which is sandwiched between the base plate and piezo-electric constraining layer. The piezo-electric constraining layer acts as an actuator that actively controls the shear deformation of the visco-elastic core according to the plate response. The ACLD patch acts as a conventional PCLD treatment when the control gain is set to zero. The effect of using a derivative control action, to control the ACLD and AC treatments, on the performance of the plate/cavity system is presented. The results obtained demonstrate the potential of the ACLD treatments in developing high damping ratios with low control voltages as compared to the AC/PCLD treatments. The developed models provide invaluable means for predicting the control of sound radiation from plates coupled to acoustic cavities, using ACLD and AC/PCLD treatments.

Analysis and control of large thermal deflection of composite plates using shape memory alloy

A finite element method for predicting critical temperature and postbuckling deflection is presented for composite plates embedded with prestrained shape memory alloy (SMA) wires and subjected to high temperatures. The temperature- dependent material properties of SMA and matrix, and the geometrical non linearities of large deflection are considered in the formulation. An incremental method consisting of small temperature increments and including the effect of initial deflection and initial stresses for materials non linearities is presented. Within each temperature increment, the Newton-Raphson iteration method is used for calculating large thermal deflection. Results show that the critical buckling temperature can be raised high enough and the postbuckling deflection can be reduced and controlled for a given operating temperature range by the proper selection of SMA volume fraction, prestrain and alloy composition.

Suppression of postbuckling deflection and panel flutter using shape memory alloy

A novel concept proposed is the use of SMA to reduce the panel thermal deflection and linear flutter responses. SMA has the unique ability of recovering large prestrain completely when the alloy is heated. During the recovery process, a large tensile recovery stress occurs if the SMA is restrained. In this paper, a panel subject to the combined aerodynamic and thermal loading is investigated. A nonlinear finite element model based on von Karman strain displacement relation is utilized to study the effectiveness of an SMA embedded panel on the flutter boundary, critical buckling temperature and post-buckling deflection. The study is performed on an isotropic panel, with embedded SMA. The aerodynamic model is based on the first order quasi-steady piston theory. The aerodynamic pressure effect on the buckling and post-buckling behavior of the panel is investigated by introducing the aerodynamic stiffness term, which changes both the critical buckling temperature and the post-buckling shape. Panels with SMA embedded in either x or y-direction and either partially or fully embedded are investigated for post-buckling behavior. Similarly, the influence of the temperature elevation on the flutter boundary is investigated by including the thermal terms.

Vibration of laminated composite plates embedded with shape memory alloy at elevated temperatures

A finite element formulation and solution procedure for the free vibration behavior of composite plates with embedded shape memory alloy (SMA) at elevated temperatures is presented. The temperature-dependent material properties of MA and composite matrix, and the geometrical nonlinearity due to large thermal deflection are considered in the formulation. The solution procedure consists of two steps: large thermal deflection is determined first, then followed by the free vibration analysis about the thermally buckled equilibrium position. Examples of hybrid composite plates are given to show the variation of lowest few frequencies versus temperature and the influence of SMA on the natural frequencies at elevated temperatures. Potential applications to frequency turning and sonic fatigue using SMA are discussed.

Flexural Vibration Control of the Circular Handlebars of a Bicycle by Using MFC Actuators

The newly developed Macro Fiber Composite (MFC) actuators are more flexible and conformable than traditional monolithic isotropic piezoceramic actuators, and capable of being surface-bonded in curved structures. In this study, both analytical prediction and experimental investigation are implemented to evaluate the effectiveness of active control of flexural vibration of the handlebars of a bicycle by using MFC actuators. The handlebars are simulated as a cantilevered hollow cylindrical rod surface-bonded with three flexible MFC actuators, two placed at the clamped end and the third at the bent location subjected to flexural vibration transmitted from a head tube. A finite element model and a Euler Bernoulli beam model are utilized to obtain the analytical predictions of natural frequencies and mode shapes of the MFC/handlebars. In the experimental verification, a primary disturbance is assumed to be transmitted from the clamped end, and a secondary force from the MFC actuators. Velocity feedback and a Linear Quadratic Regular (LQR) controller are utilized to determine appropriate voltage input into the MFC actuators. Close agreement is found between the theoretical assumptions and the experiments. The results obtained suggest that using the MFC actuators to control the flexural vibration of the MFC/handlebars of the bicycle is effective.

Control of Sound Radiation of an Active Constrained Layer Damping Plate/Cavity System Using the Structural Intensity Approach

Considerable attention has been devoted to actively and passively controlling the sound radiation from vibrating plates into closed cavities. With the advent of smart materials, extensive effort has been exerted to control the vibration and sound radiation from flexible plates using smart sensors/actuators. The Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. The treatment provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. This study investigates a numerically simulated example consisting of an ACLD treated plate/acoustic cavity system excited by a point harmonic force. In this study, an ACLD treated plate/acoustic cavity coupled finite element model is utilized to calculate the structural intensity and sound pressure radiated by the vibrating plates. In the passive control, the optimum placement of ACLD patches is determined by the structural intensity of ACLD treated plates and compared to the results obtained by using the strain energy approach. The influence on the structural intensity of the plate due to the damping treatment is investigated.

Vibration control of plates using self-sensing active constrained layer damping

Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. The treatment provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. In this study, a self-sensing configuration of the ACLD treatment is utilized to simultaneously suppress the bending and torsional vibrations of plates. The treatment considered ensures collocation of the sensors/actuators pairs in order to guarantee stable operation. A three-layer network of the Self-sensing Active Constrained Layer Damping (SACLD) treatment is used to control multi-modes of vibration of a flexible aluminum plate (0.264 m X 0.127 m X 4.826E-4 m) which is mounted in a cantilevered arrangement. Two ACLD patches (0.264 m X 0.0635 m) with self-sensing polyvinylidine fluoride (PVDF) actuators oriented by (14 degrees/-14 degrees) configuration are treated on one side of plate. The theoretical characteristics of the multi-layer treatment are presented in this paper and compared with the experimental performance.

Optimum placement and control of active constrained layer damping using the modal strain energy approach

Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. It provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. In this paper, optimal placement strategies of ACLD patches are devised using the modal strain energy (MSE) method. These strategies aim at minimizing the total weight of the damping treatments while satisfying constraints imposed on the modal damping ratios. A finite element model is developed to determine the modal strain energies of plates treated with ACLD treatment. The treatment is then applied to the elements that have highest MSE in order to target specific modes of vibrations. Numerical examples are presented to demonstrate the utility of the devised optimization technique as an effective tool for selecting the optimal locations of the ACLD treatment to achieve desired damping characteristics over a broad frequency band.