Macro Fiber Composite Actuators Research Articles

Development and Evaluation of Vibration Canceling System Utilizing Macro-Fiber Composites (MFCs) and Long Short-Term Memory (LSTM) Vibration Prediction AI Algorithms for Road Driving Vibrations.

This study developed an innovative active vibration canceling (AVC) system designed to mitigate non-periodic vibrations during road driving to enhance passenger comfort. The macro-fiber composite (MFC) used in the system is a smart material that is flexible, soft, lightweight, and applicable in many fields as a dual-purpose sensor and actuator. The target vibrations are road vibration data that were collected while driving on standard urban (Seoul) and highway roads at 40 km/s. To predict and cancel the target vibration accurately before passing it, we modeled the vibration prediction algorithm using a long short-term memory recurrent neural network (LSTM RNN). We regenerated vibrations on Seoul and highway roads at 40 km/s using MFCs and measured the displacements of the measured, predicted, and AVC vibrations of each road condition. To evaluate the vibration, we computed the root mean squared error (RMSE) and compared standard deviation (SD) values. The accuracies of LSTM RNN vibration prediction algorithms are 97.27% and 96.36% on Seoul roads and highway roads, respectively, at 40 km/s. Although the vibration ratio compared with the AVC results are different, there was no difference between the values of the AVC vibrations. According to a previous study and the principle of the AVC system, the target vibrations decrease by canceling the inverse vibration of the MFC actuator.

Aerodynamic Modeling and Design Optimization of a Variable-Camber Piezocomposite Rotor

Multirotor vehicles typically use either complex mechanisms to vary blade pitch angle or speed control to vary thrust and torque to attain stability and maneuverability. Alternatively, thrust and torque can be varied by morphing the blades without the use of complex mechanisms and without varying the rotor speed. This method could be faster to change thrust, more efficient, and it may require fewer mechanical components. This paper presents an experimentally validated aerodynamic model with an empirical static-aeroelastic correction to predict the thrust and torque coefficient of a mechanism-free rotor with Macro-Fiber Composite actuators. A variable-camber piezocomposite rotor prototype is experimentally tested on a static-thrust setup. The experiment is used to identify the so-called unknown coefficients of the model (e.g., related to the shape of the blade induced by the piezoelectric device) and to identify a correction to account for flow-induced deformations. Using the identified model, several parametric analyses are conducted to predict thrust and torque coefficients as a function of rotor speed and the electrical excitation of the piezocomposite actuators. In addition, the model is used for design optimization, leading to several optimal designs based on a limited parameter space. Three different objective functions are used: maximizing thrust, minimizing torque, and maximizing thrust-to-torque ratio. The operational aerodynamic characteristics of these designs are also presented.

Subsonic aeroelastic behaviors of a composite plate with embedded MFC actuators under hygrothermal environment

Subsonic aeroelastic effects of train-body skin structures have been intensely attractive among researchers due to the improvement of high-speed train speed. In this article, the aeroelastic behaviors of a laminated composite plate with embedded Macro Fiber Composite (MFC) actuators in hygrothermal environment under the subsonic airflow has been investigated. The Von Karman large deflection theory and the subsonic aerodynamic model based on the Bernoulli's equation are applied in the formulation. The principle of virtual work is adopted to obtain the nonlinear aeroelastic equations of the laminated composite panel with embedded MFC actuators. Subsequently, the Newmark method and Newton-Raphson method are combined to solve the framework in order to capture the nonlinear aeroelastic response of the subsonic laminated panel in time domain. Since the presence of moisture concentrations, temperature rises and applied voltages of the embedded MFC actuators will result in additional stiffness effects on composite panels by inducing prestress, thus change the aeroelastic behaviors of the composite panel, the influences of these main parameters on aeroelastic performance are analyzed. The results show that the aeroelastic flutter velocity of the composite panel gets remarkably deteriorated due to the adverse hygrothermal environment and can be strengthened through the applied voltages and appropriate lamination angles of embedded MFC actuators. Besides, the main findings of this study are the anti-symmetric laminate buckles then changes to an periodic oscillation like the limit-cycle-oscillation while there is no such phenomenon for the symmetric ones.

Underwater dynamic modeling and experiments of flexible structure with harmonic actuation of macro fiber composites

Flexible structures driven by smart actuators are promising alternatives for aquatic bionic propulsion vehicles. However, the hydrodynamic effects induced by viscous fluids on the dynamic response of flexible structures remain an ongoing challenge. Thus, this article presents a fluid-structure interaction dynamic model of a flexible underwater structure actuated by macro fiber composite actuators, and the underwater multimodal vibration characteristics are studied. The model is based on the extended Hamilton’s principle, which considers the effects of hydrodynamic forces. The segmented mode shape functions of the flexible structure are derived using the assumed mode method. The study shows that the first two mode shapes of the beam predicted by the model agrees with the experimental results. The underwater dynamic responses of the flexible structure in a board band covering the first two resonance frequencies are also investigated at different actuation levels. The underwater results indicate that the first two resonance frequencies are 1.05 and 6.1 Hz respectively, basically consistent with the simulation ones (1.07 and 6.61 Hz). Correspondingly, the maximum transverse deflections at the end of the beam are 4.81 and 1.31 mm respectively, which are slightly lower than the predicted values of 5.75 and 1.62 mm. Therefore, the validity of the proposed coupled dynamic model is verified, which can be utilized to predict the multimodal dynamic responses of underwater flexible structures actuated by MFC or other smart actuators.

Investigations on the dynamic snap-through of MFC bonded self-resetting bistable laminates

Unsymmetric composite laminates having two stable equilibrium configurations have been studied extensively in the recent past due to their potential applications in morphing structures. Surface bonded Macro Fiber Composites (MFC) actuators have been considered as a viable solution to trigger the snap-through transition in bistable laminates. Although MFC bonded bistable laminates are widely used in morphing applications, they might require considerably high voltage inputs to achieve the required levels of actuation control during the shape transition. As a solution, other possible energy sources can be combined with active MFC patches to reduce the snap-through energy required from the single source of MFC actuation. In this work, we examine the dynamic behavior of bistable composite plates actuated using MFC actuators, where external vibration energy has been used to assist with the MFC-controlled actuation between stable states. A refined semi-analytical model based on the Rayleigh–Ritz formulation has been proposed, where the membrane energy and the bending energy are separately evaluated. Bending components are directly evaluated using the approximated transverse displacement functions, whereas the membrane components are evaluated separately by combining compatibility conditions and equilibrium equations. Results from the proposed semi-analytical framework are compared with a full geometrically nonlinear finite element framework and necessary experimental observations. The results show a significant reduction in the snap-through energy demand on MFC layers where external dynamic excitation assists the snap-through process. Additionally, a parametric study is performed using variable stiffness (VS) fiber orientation parameters, achieving bistable laminate-MFC configurations that lower snap-through requirements through the proposed morphing strategy. Thus, the study offers to aid a multi-efficient snap-through strategy for the morphing of multistable composite structures.

An improved active damping of fan blade using piezoelectric MFC actuators and PSO optimization

This study introduces piezoelectric actuators for blade vibration control and aims to establish both experimental and numerical benchmarks for active vibration control with macro fiber composite (MFC) piezoelectric actuators on engine blades. It also involves optimizing the placement of MFC actuators. Experimental and numerical assessments were conducted on a 3D-printed fan model with integrated piezoelectric MFC actuators. The results confirm the effectiveness of the proposed approach, aided by a PID controller, in significantly reducing and damping blade vibrations. This comprehensive study offers a promising solution to enhance aviation engine performance and longevity.

Dynamic response of piezoelectrically actuated bistable cross-ply laminates under oscillating impulse voltages

Multistable composite laminates are ideal candidates for morphing applications due to their ability to switch between multiple stable states with proper actuation mechanisms. Surface-bonded macro fiber composite (MFC) actuators to trigger snap-through between one stable shape to another by applying external voltages have attracted considerable attention recently. In this work, dynamic snap-through of bistable unsymmetric cross-ply laminate using MFC actuators under oscillating impulse voltages has been investigated. Both unimorph and bimorph laminate-MFC configurations are considered for the analysis. The stable equilibrium configurations of the MFC-actuated bistable laminate, considering the effects of MFC bondage, are discussed using the proposed finite element (FE) framework. Under the action of oscillating impulse voltages, the single-well and cross-well oscillations of the active bistable plate are analyzed in detail through time responses and phase portraits. The FE results show the advantage of actuating MFC layers through the oscillating impulse voltages as it leads to a reduction in the maximum snap-through voltage requirements.

Adaptive iterative learning control and inverse compensation of macro fiber composite system with hysteresis

Macro fiber composite (MFC) actuators, which exhibit excellent flexibility and strong deformability, are widely used in aerospace exploration, flexible robotics, and other applications. However, the rate-dependent hysteresis nonlinearity of the flexible beam driven by MFCs significantly affects positioning accuracy. This study utilizes a new Hammerstein model to describe the hysteresis of an MFC system and proposes a control strategy that combines adaptive iterative learning control and inverse compensation. The adaptive iterative learning control allows the learning gain parameters to be adjusted based on the tracking error. A high gain ensures the convergence speed of iterative learning, whereas a small learning gain provides high robustness and convergence accuracy. Trajectory tracking experiments are conducted to verify the effectiveness of the proposed control strategy. Compared with the case of direct inverse compensation, after the sixth iteration, the tracking maximum absolute error, relative error, and corresponding root mean square error of the proposed control strategy reduce by 73% on average. Moreover, compared with the case of P-type iterative learning control combined with inverse compensation, the metrics above reduce by 12% on average. The proposed control strategy offers higher tracking accuracy and greater practicality in the trajectory tracking of MFC systems.

Damage detection and localization based on different types of actuators using the electromechanical impedance method in 3D-printed material

Electromechanical impedance (EMI) measurement, using piezoelectric transducers (PZTs) in the high-frequency range is a potential method for assessing the health of lightweight structures. The major objective of this work is to comprehend how different actuators react to damage in additively manufactured (AM) polymer structures. A novel frequency-range selection technique was suggested based on the maxima of the standard deviation of the impedance frequency spectra gathered for the referential and damage cases. A 3D-printed acrylonitrile butadiene styrene (ABS) plate was used for the investigation, where two PZT and one macro fiber composite (MFC) actuator were glued to the surface. Small magnets were used to simulate damage and were positioned at increasing distances from each transducer as EMI measurements were made using the MFC and 1 PZT. This served both in studying the transducers’ sensitivity to damage and selecting the proper frequency range for damage detection utilizing the standard-deviation approach. The EMI-acquired data from the MFC actuator displays damage-sensitive peaks in a low-frequency band (0–58 ), while the PZT shows a good sensitivity in a higher frequency range (94–304 ). In order to evaluate the PZT and MFC actuators’ sensitivity to damage in the 3D-printed ABS plate, impact damage is also generated in the plate’s center. The impedance-based damage indices obtained from different types of PZTs (2 PZTs and 1 MFC) were projected to the same base level and then fused—for the first time—for impact-damage localization and further added magnetic mass damage localization. The obtained damage index values of impedance are encouraging for the evaluation of AM polymer structures with a 4.48 mm positional error from a real location by fusing data in the different frequency ranges for PZTs and MFC. The damage localization error increases significantly to the new location beyond the damage sensitivity range of the PZT2 and MFC for the added magnetic mass on the 3D printed structure.

Experimental investigation of vibration amplitude control in additive manufactured PLA and PLA composite structures with MFC actuator

In this study, Macro Fiber Composite (MFC) as actuator has been used for open-loop active vibration control (AVC) in additive manufactured structures made of polylactic acid (PLA) and PLA composites, such as PLA with short carbon fibers (PLA-SCF composite) and PLA with continuous carbon fibers (PLA-CCF composite), when subjected to forced vibrations. The laser vibrometer has been used to find the natural frequencies and bending mode shapes of each beam structure. The MFC patch (M8507-P2), used here as an actuator, is very sensitive to supplied voltages. Thus, it is very crucial to find out the optimum phase and amplitude of the input voltage. The optimal phase angle and voltage for each structure (PLA, PLA-SCF, PLA-CCF) are estimated by a domain search in an incremental manner. Once tuned with the optimal input voltage values, the proposed technique shows exceptional performance in vibration suppression. The results confirmed that this technique can be used in a wide range of composite materials.

Fatigue Crack Growth Mitigation by In Situ Healing in Thermoset CFRP Composite

Delamination due to fatigue loading in laminated composites is difficult to detect and, therefore, could lead to catastrophic failure if left undetected. Hence, it is important to be able to detect and quantify the delamination crack growth behavior due to fatigue loading and explore methods to heal the delamination in situ, without the need for mechanical fasteners. To this end, double cantilever beam specimens of carbon-fiber-reinforced polymer composite containing thermoplastic healants were manufactured, and mode I fatigue delamination experiments were carried out for the virgin and healed cases for oven healing, and in situ macro fiber composite healing cases. The primary purpose of using thermoplastic healants (polycaprolactone and shape memory polymer) was to heal the cracks formed during fatigue loading and regain the load-carrying capacity of the composite structure. The in situ healing was carried out by activating the macro fiber composite actuators attached to the double cantilever beam specimen after 5000 cycles of loading to generate heat. After in situ healing, significant reduction in crack growth compared to the virgin cycle was observed, and healing was repetitive. We envision that these findings will be immensely helpful in extending the service life of composites and may also result in significant repair cost savings.

Modeling and active control of geometrically nonlinear vibration of composite laminates with macro fiber composite

To study the active control of the geometrically nonlinear vibration of flexible composite laminates, it is necessary to create its dynamic model and predict the effect of vibration reduction. In this paper, geometrically nonlinear and active control are introduced through von Kármán large deformation theory and velocity feedback controller, respectively. On this basis, the active control model of geometrically nonlinear vibration of composite laminates with macro fiber composite (MFC) is established. For solving the nonlinear model, an improved Newmark-β method is proposed for solving differential equations with nonlinear terms, which has better consistency and higher solution efficiency than the classical fourth-order Runge-Kutta solution. The suppression effect of active control on the nonlinear vibration response of the structure and the accuracy of the geometrically nonlinear model are confirmed using the composite cantilever laminates with MFC sensor/actuator as an example. Based on the nonlinear model, the influence of the control gain and the different positions of the MFC actuators on the active control effect are analyzed, and then the appropriate control gain and the better position of the MFC are determined.

Lead-free piezoceramic macro-fiber composite actuators toward active vibration control systems

Macro-fiber composite actuators (MFCAs) suffer from strict restrictions on the utilization of lead-containing precursors due to growing environmental concerns. To address this issue, a novel lead-free MFCA based on potassium sodium niobate piezoceramics has been developed using the dice & fill method. The MFCA demonstrates large electric field-induced displacement (31.4 μm over -500‒1 500 V at 0.5 Hz), excellent frequency stability, and a strong linear relationship between the induced displacement and the external voltage amplitude. Meanwhile, unlike lead-based MFCA that requires superposition of a negative dc bias voltage to pursue higher output performance but risks depolarization, lead-free MFCA can achieve larger displacement by superimposing only a positive bias voltage. This device exhibits excellent reliability, maintaining a stable output over 105 electrical cycles. Additionally, a “back-to-back” coupled MFCA has been developed to regulate bidirectional displacement, making it suitable for various practical applications, including active vibration control. This approach has resulted in a 90% vibration reduction and provides new insights into the design of MFCAs, further facilitating their application in active vibration control systems.

Electro-mechanical analysis of functionally graded graphene reinforced composite laminated plate with macro fiber composite actuator

Graphene is considered to be a desirable reinforcement material for composite materials due to its exceptional mechanical properties. However, there is a lack of research on the interlaminar stress analysis of graphene reinforced composite plates bonded with a macro fiber composite (MFC) actuator subjected to electro- mechanical loads. Inaccurate descriptions of interlaminar shear deformations can significantly affect the mechanical performance of the MFC piezoelectric graphene reinforced composite plate due to the electro-mechanical coupling feature and abrupt change in material properties at the interfaces of neighboring layers. To address this issue, this study proposes an attractive plate model for the analysis of MFC piezoelectric laminated plate. The three-dimensional (3D) elasticity equations and the Reissner mixed variational theorem (RMVT) are employed to improve the precision of interlaminar shear stresses. The 3D elasticity solutions and results obtained from other models are used to evaluate the proposed model. Furthermore, this study thoroughly investigates the effect of several significant parameters on the deformations and stresses of the MFC piezoelectric plates with reinforcements.

Underwater dynamic hysteresis modeling and feedforward control of flexible caudal fin actuated by macro fiber composites

Underwater bionic robotics and vehicles that use flexible structures as power sources have attracted considerable attention. Thus, the underwater dynamic behaviors of the flexible structure of a variable cross-section actuated by smart actuators must be further investigated. In this study, underwater dynamic hysteresis modeling and feedforward compensation of a flexible caudal fin driven by macro fiber composites (MFC) at different frequencies were investigated. The MFC-actuated flexible caudal fin is considered a Euler–Bernoulli beam. A revised hydrodynamic function governed by the thickness of the viscous layer and the gap-to-width ratio of the cross-section was developed. Then, a characteristic-frequency-dependent extended transform function model is proposed for the hydrodynamic response of a non-uniform beam. An asymmetric hysteresis model is presented to characterize the rate-independent hysteresis behavior of the MFC actuators. Further, the underwater dynamic equation of the MFC-actuated caudal fin with hysteresis is obtained by connecting the two established models in series. Experiments demonstrate the dynamic behavior between the underwater responses of the caudal fin and the input voltages have an ellipse-like shape and vary in shape and size with oscillating frequency. The ellipse-like dynamic hysteresis loop first grows, reaching its maximum at the resonant frequency, and then decreases, because of the frequency-dependent dynamic behavior. Meanwhile, a phase shift of approximately 90°between the input voltage and underwater dynamic response was observed at the resonant state. Furthermore, the experimental results demonstrate that the proposed model can describe the nonlinear underwater dynamic hysteresis behavior of the proposed caudal fin at different frequencies. The trajectory tracking performances are remarkably improved over a broad frequency range with the proposed compensator. Consequently, the effectiveness of the proposed dynamic model and compensation method was demonstrated. These results are helpful for robotic fish or autonomous underwater vehicles propelled by oscillating foils actuated by smart actuators, including MFC.

Macro Fiber Composite-Actuated Soft Robotic Fish: A Gray Box Model-Predictive Motion Planning Strategy Under Limited Actuation.

This work experimentally investigates a model-predictive motion planning strategy to impose oscillatory and undulation movements in a macro fiber composite (MFC)-actuated robotic fish. Most of the results in this field exploit sinusoidal input signals at the resonance frequency, which reduces the device's maneuverability. Differently, this work uses body/caudal fin locomotion patterns as references in a motion planning strategy formulated as a model-based predictive control (MPC) scheme. This open-loop scheme requires the modeling of the device, which is accomplished by deriving a gray box state-space model using experimental modal data. This state-space model considers the electromechanical coupling of the actuators. Based on the references and the model, the MPC scheme derives the input signals for the MFC actuators. An experimental campaign is carried out to verify two references for mimicking the locomotion patterns of a fish under limited actuation. The experimental results confirm the motion planning scheme's capability to impose oscillatory and undulation movements.

Repeatable self-healing of composite’s fatigue delamination

This paper investigates repeatable self-healing of composite laminates to mitigate fatigue delamination where a two-step healing mechanism is employed to heal the delamination cracks in a CFRP composite: (i) close the cracked surfaces by thermally activating dispersed shape memory polymer (SMP) filaments, and (ii) heal the closed crack by melting the thermoplastic healant (PCL) dispersed in the thermoset polymer matrix and allowing it to flow into the cracked region and solidify. Repetitive self-healing is carried out on double cantilever beam (DCB) specimens using macro fiber composite (MFC) actuators bonded to the test specimens, which generate the heat required to activate the thermoplastic healants to heal the delamination in the composite. Fatigue delamination growth rates were obtained for replicate specimens to extract statistically meaningful data on fatigue life under mode-I loading after seven healing cycles, indicating substantial retardation in delamination growth rate resulting in a significant increase in fatigue life.

Performance enhancement of a bioinspired micro air vehicle by integrating a smart composite in its morphing wing

The purpose of this paper is to show the advantages of using a smart composite in a micro air vehicle (MAV) equipped with morphing wing technology. A Macro Fiber Composite (MFC) actuator is attached to the wing’s bottom surface to modify the wing camber during the mission. This material allows the MAV to be optimized according to each flight, thus making it more versatile and attractive to the market. The elongation of the lower surface when a positive voltage is applied to the actuator is translated to an increment in camber, which results in an increment in the maximum lift coefficient, thus enabling the vehicle to fly slower to adapt to any payload. Besides, a reduction in camber results in an increase in aerodynamic efficiency, which improves range and endurance. Several tests of the MAV at prototype level have been carried out at INTA, so as to demonstrate the feasibility of implementing MFC actuators to control and manoeuvre these vehicles. The use of this material in aerospace industry opens up various fields of research in aerospace engineering, such as new features in flight mechanics and aerodynamic performance and new strategies in the design of flight stability and control laws.

Aero-structural optimization and actuation analysis of a morphing wing section with embedded selectively stiff bistable elements

Morphing wings provide a potential avenue to improve aerodynamic performance of aircraft operating at multiple design conditions. Nevertheless, morphing wing design is constrained by the mutually exclusive goals of high load-carrying capacity, low weight, and sufficient aerodynamic control authority via conformal shape adaptation. This trade-off can be addressed by exploiting the stiffness selectivity and shape “lock-in” properties enabled by using bistable beam-like elements within compliant structures. In this paper, we present an aero-structural optimization method to realize morphing structures with selective stiffness and shape “lock-in” capability from embedded bistable elements. We leverage an embeddable beam element with an invertible curved arch that provides stiffness selectivity and camber variation to the proposed rib geometry. Optimization objectives and constraints are designed to maximize the structure’s stiffness change and camber morphing “lock-in” effect when operating at two distinct flight conditions. Using the optimization results, we manufacture a wing section demonstrator with selective stiffness and “lock-in” morphing featuring two optimized ribs, a load-carrying skin made of a carbon reinforced laminate, Macro-Fiber Composite (MFC) actuators, and a servo-controlled mechanism for switching the bistable elements’ states. The power and energy requirements of actuating and holding a target deflection are experimentally measured and compared. The results show that the bistable elements can assist in holding a target deflection at a reduced energy cost. Finally, we test the experimental demonstrator in a low-speed wind tunnel demonstrating the load carrying capability and lift variation achieved from switching states.

Research on Asymmetric Hysteresis Modeling and Feedforward Compensation of Macro Fiber Composite Actuator

Research on Asymmetric Hysteresis Modeling and Feedforward Compensation of Macro Fiber Composite Actuator