Adaptive Composite Structures Research Articles

Active and passive multicycle actuation characteristics of shape memory alloy-based adaptive composite structures

Shape memory alloys (SMAs) offer an attractive way to build adaptive structures as their shape changes and remembered their shape under the applied external stimuli. The adaptive composite structures embedded with SMA wires have been developed using the hand layup process. In this work, the experimental investigation of the actuation behaviour of the SMA-based adaptive composite structures was carried out. This is achieved by imposing external active and passive heating. To investigate the actuation behaviour of the SMA-based adaptive composite structure different diameters of SMA wires and their configurations were considered. Based on the trial experiments, a voltage of 6 V, a heating time of 5 s, and a cooling time of 18 s have been optimized for electrical heating. These heating conditions were used for all the thermomechanical analysis of SMA-based adaptive composite structures and all the samples were tested for multiple cycles of heating and cooling. The maximum deflection of 14 mm was observed for the composite structure embedded with four SMA wires of 0.5 mm diameter. Our fundamental study highlights the possibility of using SMA-based adaptive structures in electromechanical systems such as actuators and sensors.

4D Printing Self-Morphing Structures.

The main objective of this paper is to introduce complex structures with self-bending/morphing/rolling features fabricated by 4D printing technology, and replicate their thermo-mechanical behaviors using a simple computational tool. Fused deposition modeling (FDM) is implemented to fabricate adaptive composite structures with performance-driven functionality built directly into materials. Structural primitives with self-bending 1D-to-2D features are first developed by functionally graded 4D printing. They are then employed as actuation elements to design complex structures that show 2D-to-3D shape-shifting by self-bending/morphing. The effects of printing speed on the self-bending/morphing characteristics are investigated in detail. Thermo-mechanical behaviors of the 4D-printed structures are simulated by introducing a straightforward method into the commercial finite element (FE) software package of Abaqus that is much simpler than writing a user-defined material subroutine or an in-house FE code. The high accuracy of the proposed method is verified by a comparison study with experiments and numerical results obtained from an in-house FE solution. Finally, the developed digital tool is implemented to engineer several practical self-morphing/rolling structures.

Uncertainty assessment of coupled Digital Image Correlation and Particle Image Velocimetry for fluid-structure interaction wind tunnel experiments

The development of advanced composite structures for maritime and aerospace applications requires the ability to quantify their actual performance under known fluid loads. One example is the need to investigate the differences in fluid–structure response of passive adaptive composite structures. A wind tunnel based method is used to quantify the structural behaviour, and fluid response, of a flexible aerofoil under fluid loading. The technique measures the deflection of the structure, with high speed stereoscopic Digital Image Correlation (DIC). The tip vortex position is measured using high resolution stereoscopic Particle Image Velocimetry (PIV). The accuracy of the two full-field optical measurement systems is quantified and the effect of optical interactions is assessed. A flexible NACA0015 rectangular plan-form aerofoil of 0.9m span and aspect ratio of two is subjected to aerodynamic loading within a closed circuit wind tunnel. The wind speed was varied from 10 to 25m/s within a 3.5m x 2.4m working section. The structural response is measured simultaneously with the fluid flow field around the tip vortex. The tip vortex core, which moved by ≈62mm at the highest wind speed, is directly compared to the deformation of the structure, which deflected by ≈58mm. A maximum foil twist of ≈0.6° was observed. The DIC accuracy is evaluated in static and transient conditions for translational and rotational movement. The DIC maximum error for translations, greater than or equal to 0.5mm, is less than 3% and less than 0.6% in dynamic motions. The DIC total error for rotations is less than 5% in static motions and 1% in dynamic rotations. The PIV uncertainty is quantified a posteriori providing the errors due to the correlation algorithm and the experimental setup. The mean in-plane velocity component uncertainties in the vortex region varied between 1.2% and 3.5% depending on flow speed (≈0.1px). The mean out-of-plane velocity uncertainty around the vortex varies between 2% and 3.3% depending on flow speed.

Studies on the polarisation behaviour of novel piezoelectric sensor modules

A novel approach to the manufacture of adaptive composite structures with integrated piezoelectric modules focusses on combining the previously separate production steps – production of the piezoceramic transducer, composite fabrication and integration of the transducers – into an efficient single-stage process. Based on the long fibre injection (LFI) technology, a novel multi fibre injection (MFI) method is developed. By integrating piezoceramic components like short fibres or pearls and suitable electrode structures into the composite, novel piezoelectric functional elements are created and embedded during the structure's manufacturing process. For the functionalisation of these elements, mainly to provide sensory properties, poling of the piezoceramic components during or after the production process is required. Based on initial simulations of electric field strength, poling process and resulting small signal properties, conclusions for an adapted poling strategy of these novel sensor modules are elaborated.

Process Chain Modelling and Analysis for the High-Volume Production of Thermoplastic Composites with Embedded Piezoceramic Modules

Active composite structures based on thermoplastic matrix systems are highly suited to applications in lightweight structures ready for series production. The integration of additional functional components such as material-embedded piezoceramic actuators and sensors and an electronic network facilitates the targeted control and manipulation of structural behaviour. The current delay in the widespread application of such adaptive structures is primarily attributable to a lack of appropriate manufacturing technologies. It is against this backdrop that this paper contributes to the development of a novel manufacturing process chain characterized by robustness and efficiency and based on hot-pressing techniques tailored to specific materials and actuators. Special consideration is given to detailed process chain modelling and analysis focusing on interactions between technical and technological aspects. The development of a continuous process chain by means of the analysis of parameter influences is described. In conclusion, the use of parameter manipulation to successfully realize a unique manufacturing line designed for the high-volume production of adaptive thermoplastic composite structures is demonstrated.

Influence of uncertainties on the response and reliability of self-adaptive composite rotors

Advanced composite structures are becoming increasingly popular because of their high specific strength and stiffness, as well as ability to provide improved performance through passive morphing via intrinsic bend–twist deformation coupling. Self-adaptive composite structures tend to be more susceptible to geometric, material, and loading uncertainties because of their complex configuration, manufacturing process, and dependence on fluid–structure interaction (FSI) response. The objective of this work is to quantify the effects of material, geometric, and loading uncertainties on the response of self-adaptive composite propellers and overall system reliability. A fully-coupled, 3-D boundary element method–finite element method is used to compute the dynamic FSI response. Variability in propeller performance is estimated by considering variations in operating conditions, as well as blade geometry and stiffness. Modeling uncertainties are considered by employing various mechanistic-based failure initiation models. Random variations in material strengths are implemented and an estimate of the structural reliability is determined. The results indicate that adaptive composite structures that depend on FSI are more sensitive to natural, random variations than equivalent rigid, isotropic structures. Therefore, it is necessary to quantify the effects of material, geometric, and loading uncertainties on the responses, safe operating envelopes, and reliability of self-adaptive composite structures.

Development of novel piezoceramic modules for adaptive thermoplastic composite structures capable for series production

The use of adaptive composite structures in series applications requires novel actuators and related manufacture processes capable for serial production. The paper shows latest research results with regard to the continuous development of novel thermoplastic-compatible piezoceramic modules (TPM). These modules are predestined for the material homogeneous actuator integration in fibre-reinforced thermoplastic composites by means of a welding process. The research focuses on numerical and experimental studies in order to design efficient modules capable for a continuous production process. Especially studies with regard to geometrical parameters and their influences on the actuator performance as well as studies with respect to the manufacture process are accomplished.

Piezoelectric Fiber Composites as Sensor Elements for Structural Health Monitoring and Adaptive Material Systems

Piezoelectric Active Fiber Composites (AFC) and Macro Fiber Composites (MFC) have the potential to provide various sensor functions for nondestructive test methods. AFC have been integrated into fiber-reinforced laminates as a first step towards structures with sensing capability. These developments constitute initial stages for developing adaptive composite structures or structures with integrated health monitoring system. So far, the use of AFC and MFC has been explored in selected nondestructive tests for defect detection in model composite systems on laboratory scale with e.g., Acoustic Emission, Acousto-Ultrasonics, and Electromechanical Impedance testing. The present article will focus on limitations and current prospects for structural health monitoring with AFC or MFC and discuss selected concepts and approaches.

Fabrication of metal–matrix composites and adaptive composites using ultrasonic consolidation process

Ultrasonic consolidation (UC) has been used to embed thermally sensitive and damage intolerant fibres within aluminium matrix structures using high frequency, low amplitude, mechanical vibrations. The UC process can induce plastic flow in the metal foils being bonded, to allow the embedding of fibres at typically 25% of the melting temperature of the base metal and at a fraction of the clamping force when compared to fusion processes. To date, the UC process has successfully embedded Sigma silicon carbide (SiC) fibres, shape memory alloy wires and optical fibres, which are presented in this paper. The eventual aim of this research is targeted at the fabrication of adaptive composite structures having the ability to measure external stimuli and respond by adapting their structure accordingly, through the action of embedded active and passive functional fibres within a freeform fabricated metal–matrix structure. This paper presents the fundamental studies of this research to identify embedding methods and working range for the fabrication of adaptive composite structures. The methods considered have produced embedded fibre specimens in which large amounts of plastic flow have been observed, within the matrix, as it is deformed around the fibres, resulting in fully consolidated specimens without damage to the fibres. The microscopic observation techniques and macroscopic functionality tests confirms that the UC process could be applied to the fabrication of metal–matrix composites and adaptive composites, where fusion techniques are not feasible and where a ‘cold’ process is necessary.

Modeling and Optimization of Passively Damped Adaptive Composite Structures

A smart structural model is used to optimally determine both the placement of piezoelectric actuators and parameters describing associated electrical components in a passively damped structure. The technique utilizes a recently developed coupled piezoelectric-mechanical theory to analytically determine the response of arbitrary structures with piezoelectric materials and attached electrical circuitry. The theory simultaneously models both the structural and the electrical components, and the complex state of strain that may exist in the piezoelectric patches, thereby providing accurate mechanical and electrical response. A robust multiobjective optimization procedure is developed to design the passive system for simultaneous damping of several critical modes of interest. The influence of stacking sequence in augmenting passive damping can also be examined by including ply orientations as design variables. Since the optimization problem now involves both continuous and discrete design variables, a hybrid optimization technique is used that allows the inclusion of both types of design variables. Also, since multiple design objectives are introduced, the Kreisselmeier-Steinhauser function approach is used allowing the multiple and conflicting design objectives and constraints to be combined into a single unconstrained function. Results demonstrate the ability of this technique to determine the optimal tuning parameters for damping of multiple modes of vibration using a limited number of piezoelectric actuators.

FEM modeling of adaptive composite structures using a reduced higher-order plate theory via penalty functions

Abstract This paper presents a finite element model for analyzing the composite laminates containing the piezoelectrics statistically or dynamically. First, to model the moderately thick laminated plates, a simple higher-order plate theory, which can satisfy the free conditions of transverse shear strains on the top and bottom surfaces of plates, have been adopted. To set up a C 0 -type FEM scheme, two artificial variables in the displacement field have been introduced to avoid the higher-order derivatives from the higher-order plate theory. The corresponding constraint conditions from two artificial variables have been enforced effectively through the penalty function method using the reduced integral scheme within the element area. Second, a generalized coupling FEM model for the mechanical and electric fields from the variational framework have been proposed. Finally, various examples studied in many previous researches have been employed to verify the justification, accuracy and efficiency of the present model.

Modelling and design of adaptive composite structures

Recent developments in adaptive composite structures with distributed piezoelectric actuators and sensors have attracted significant attention in the research community due to their potential commercial benefits in a wide range of applications such as vibration suppression, shape control, noise attenuation and precision positioning. The complexity in the design and fabrication of the adaptive laminated composites has resulted in a need to develop reliable and refined models to study their material properties and mechanical behaviour. Here, higher order finite element formulations and an analytical closed form solution have been developed to study the mechanics of adaptive composite structures with embedded and/or bonded piezoelectric actuators and sensors. Optimization of adaptive composite structures is also an important design aspect in order to maximize actuator performance. Two optimization schemes are considered in this study where the design variables are the layer thickness, actuator size and location. To demonstrate the validity, usefulness and efficiency of the proposed models several illustrative examples are presented and discussed.

Adaptive composites modelling and application in panel flutter and noise suppression

Recent developments in adaptive composite structures with distributed multifunctional actuators and sensors have attracted significant attention in the research community due to their potential commercial benefits in a wide range of applications such as vibration suppression, shape control and noise attenuation.In the field of finite element modeling, very few composite shell elements with electromechanical properties have been reported in the literature. Also, the reported finite elements used to model aircraft components have not properly accounted for the effects of curvature, thus requiring refined meshes in order to capture accurately the physics of the problem. The model proposed in this investigation consists of a shell type adaptive composite finite element with electromechanical properties and with double curvature. Its application in aircraft flutter and internal noise suppression are investigated.

Smart Materials Based on Shape Memory Alloys: Examples from Europe

Shape Memory Alloys (SMAs) have become increasingly attractive as embedded actuators in polymers yielding adaptive composite structures. In particular, SMA-elements have been used to actively or passively control shape, elastic modules, internal stress level and damping capacity of such smart composites. In the passive approach, copper-base SMA-plates can be used as temperature-sensitive damping elements, an interesting solution to improve the vibrational behaviour of alpine skis for example. Active materials are obtained by the integration of pre-strained Ni-Ti-base thin wires in polymer matrix composites enabling control of the vibrational behaviour through the recovery-stress tuning technique. In this paper, some results of national research programmes in Belgium and Switzerland, mainly concerning the damping capacity, are shown and a new European project entitled Adaptive Composites with Embedded Shape Memory Alloy Wires is presented in which partners from Belgium, Germany, Greece, Great Britain and Switzerland are collaborating.

Structural integrity issues during piezoelectric vibration suppression of composite structures

Abstract Piezoelectric materials are one of a group of materials used to construct smart or adaptive structures. The control of structural vibrations is a promising real-world application of this technology for aerospace structures. The modeling and application of piezoelectric vibration suppression technology is reviewed—concentrating on the notable work of the past decade. Several real-world aerospace applications are also discussed demonstrating the near-term promise of this technology. Next the structural issues are reviewed establishing that a very limited knowledge of fatigue and fracture behavior for the adaptive composite structures exist. Therefore, increased attention to structural integrity of the vibration suppression systems is required before their real-world application can commence.

Multi-Objective Optimization of an Adaptive Composite Beam Using the Physical Programming Approach

The objective of this paper is to present the optimization of an adaptive composite structure using the physical programming approach. To this end, a multi-objective optimization problem of an adaptive composite beam with piezoelectric actuators bonded to its surface is performed. The goal is to optimize the size and placement of the actuator pairs, in order to maximize the performance of their actuation power, to minimize the mass of the piezoelectric material and to maintain the required actuation voltages below maximum operating values. A generalized tri-dimensional version of the Heaviside function has been used to represent the distribution of the piezoelectric actuators. A closed form solution for the equations of equilibrium is presented. Physical programming presents the following advantages over the more conventional optimization methodologies: reduced computational effort and time, elimination of both iterative selection of weights and prioritization of objective functions.