Commercial aircraft today require efficient high-lift and control systems on the wings to reduce the drag in flight or decrease the take-off and landing speeds. Morphing mechanisms are one approach for improved high-lift systems. In most cases the objective function is an increased lift to drag ratio or the noise reduction. On closer examination control systems as well as morphing mechanisms are located in a certain wing segment. The transition between a moving wing part and the fixed wing is a step, which creates additional vortices. This segments the wing in span-wise direction and reduces the efficiency. A flexible skin between a moving and a fixed wing parts smooths the contour and minimize the efficiency reduction of the wing. A full scale demonstrator of a wing segment was manufactured with two flexible skin designs. The first subcomponent connects a morphing leading edge with a rib of the wing over a span of one meter. The skin is a material mix of ethylene-propylene-diene monomer (EPDM) rubber and fiberglass-reinforced plastic. The rubber is the basis of the skin and the glass-fiber is added as local skin stiffeners in the form of strips in chord-wise direction. The second subcomponent blends the aileron with a rib of the wing in a triangular design. The connection of three different hinges realizes a morphing triangle, which is loaded in an in-plane shear only state of stress in each aileron position. The core of the triangle is a 3D printed structure, which is free in shear. The covering skin is a combination of EPDM with carbon fibers oriented in +/−30° direction to obtain shear compliance and to resist the loads on the triangle. The deformation of each concept is identified at the demonstrator. Therefore, an optical measurement system scans the surface in the initial and deflected state. The required deformation precision of the concepts differs due to their design. The contour at the leading edge requires a certain shape over the span. The analysis of the skin buckling is one requirement at the transition triangle during the aileron motion. The experimental results show a smooth transition contour at the leading edge and no buckling effects at the triangle. The results can be used for the validation of simulation models. Furthermore, both skin concepts cover the gap between a moving wing segment and a fixed wing part. The elimination of steps in span-wise direction can improve the aero-acoustic behavior along the wing for future aircraft.

Honeycomb composites are common materials in applications where a high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the effective properties of these honeycomb polymer composites is limited, thus further research is needed to better characterize the behavior of these materials. In this work, a nonlinear finite element analysis was employed to perform parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A pinned rigid wall model was created as an upper bound on the deformable wall model’s performance, and an empty honeycomb model was employed to better understand the mechanisms of stiffness amplification. Mechanisms by which the stiffness amplification occurs is studied through parametric studies, and the results are compared to current analytic models. It has been observed that both the volume change within the honeycomb cell under deformation, and the mismatch in Poisson’s ratios between the honeycomb and infill influence the effective properties. Stiffness amplifications of over 4,000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. This research provides an important step toward understanding the design space and benefits of honeycomb polymer composites, and demonstrates the possibilities for variable stiffness structures when considering smart material infill materials.

Composites can be tailored to specific applications by adjusting process variables. These variables include those related to composition, such as volume fraction of the constituents and those associated with processing methods, methods that can affect composite topology. In the case of particle matrix composites, orientation of the inclusions affects the resulting composite properties, particularly so in instances where the particles can be oriented and arranged into structures. In this work, we study the effects of coupled electric and magnetic field processing with externally applied fields on those structures, and consequently on the resulting material properties that arise. The ability to vary these processing conditions with the goal of generating microstructures that yield target material properties adds an additional level of control to the design of composite material properties. Moreover, while analytical models allow for the prediction of resulting composite properties from constituents and composite topology, these models do not build upward from process variables to make these predictions. This work couples simulation of the formation of microscale architectures, which result from coupled electric and magnetic field processing of particulate filled polymer matrix composites, with finite element analysis of those structures to provide a direct and explicit linkages between process, structure, and properties. This work demonstrates the utility of these method as a tool for determining composite properties from constituent and processing parameters. Initial particle dynamics simulation incorporating electromagnetic responses between particles and between the particles and the applied fields, including dielectrophoresis, are used to stochastically generate representative volume elements for a given set of process variables. Next, these RVEs are analyzed as periodic structures using FEA yielding bulk material properties. The results are shown to converge for simulation size and discretization, validating the RVE as an appropriate representation of the composite volume. Calculated material properties are compared to traditional effective medium theory models. Simulations allow for mapping of composite properties with respect to not only composition, but also fundamentally from processing simulations that yield varying particle configurations, a step not present in traditional or more modern effective medium theories such as the Halpin Tsai or double-inclusion theories.

As materials and engineering design tools become more complex, engineers are looking to mimic structures and systems, occurring in nature, to design more efficient mechanical structures. One such structure is a morphing composite lattice structure, whose design was inspired by the tail of the bacteriophage T4 virus [1]. To date the morphing behavior of the tail structure of the virus has been simplified by neglecting the intermolecular mechanisms that actuate the bistable behavior of the tail. This behavior has been achieved using prestressed composite flanges that are mechanically joined in alternating clockwise and anti-clockwise chiralities. The composite lattice structure has previously been proposed as an actuator for aerospace structures, replacing more complex and heavier traditional actuator structures. McHale et al. [2] have shown that the composite lattice is capable of greatly improving upon the state-of-the-art in the form of a telescopic boom for CubeSat systems. This utility provides validity in studying further enhancements on the capabilities of the structure to enhance its potential applications in the aerospace industry. This work proposes a mechanism for replicating the inter-molecular behavior that occurs in the bacteriophage T4 tail. The bonds between the inner and outer tail structures are broken and reformed, thus, driving the actuation process. This method will form a variable topology morphing system. As such, a novel category of morphing structure is presented here for the first time. The morphing topology behavior is proposed by replacing mechanical fasteners in the traditional lattice structure in select locations with a series of permanent magnets. Finite element analysis is used to calculate the difference in energies between the states before and after discrete topology changes occur, allowing the associated change in energy to be converted to a required actuation force. Varying the topology of the lattice structure allows the lattice to transition from a linear morphing actuator system to a bespoke and tunable curved actuator with potential applications in satellite dish actuation, for example.

This paper proposes a highly stretchable strain sensor using viscous conductive materials as resistive element and introduces a simple and economic fabrication process by encapsulating the conductive materials between two layers of silicone rubbers Ecoflex 00-30. The fabrication process of the strain sensor is presented, and the properties of the viscous conductive materials are studied. Characterization shows that the sensor with conductive gels, toothpastes, carbon paint, and carbon grease can sustain a maximum tensile strain of 200% and retain good repeatability, with a strain gauge factor of 2.0, 1.75, 3.0, and 7.5, respectively. Furthermore, strain sensors with graphite and carbon nanotubes mixed with conductive gels are fabricated to explore how to improve the gauge factor. With a focus on the most promising material, conductive carbon grease, cyclic stretching tests are conducted and show good repeatability at 100% strain for 100 cycles. Lastly, it is demonstrated that the stretchable strain sensor made of carbon grease is capable of measuring finger bending. With its easy and low-cost fabrication process, large strain detection range and good gauge factor, the conductive materials-based strain sensors are promising for future biomedical, wearable electronics and rehabilitation applications.

In the last decade, the adoption of additive manufacturing technologies (AMT) (3D printing) has increased significantly in many fields of engineering, initially only for rapid prototyping and more recently also for the production of finished parts. With respect to the long-established material subtractive technologies (MST), AMT is capable to overcome several limitations related to the shape realization of high-performance mechanical components such as those conceived via topology optimization and generative design approaches. In the field of structures and mechanisms, a major advantage of AMT over MST is that, for the same loading and constraining conditions (including kinematic and overall encumbrance), it enables the realization of mechanical components with similar stiffness but smaller volume (thus smaller weight, density being equal). Recently, the potentialities of AMT have also been increased by the introduction of the fuse filament deposition modeling (FDM) of continuous fibre-reinforced thermoplastics (CFRT), which combines the ease of processing of plastic AMT with the strength and specific modulus of the printed components that are comparable to those attainable via metallic AMT. In this context, the present paper investigates the potentialities of FDM-CFRT for the realization of mechanisms subjected to predominant inertial loads such as those found in automated packaging machinery. As a case study a Stephenson six-bar linkage powered in direct drive by a permanent magnet synchronous motor is considered. Starting from an existing mechanism realized in aluminum alloy with traditional MST, a newer version to be realized with FDM-CFRT has been conceived by keeping the kinematics fixed and by redesigning the links via three-dimensional topology optimization. To provide a fair comparison with the more traditional design/manufacturing approach, size optimization of the original mechanism made in aluminum alloy has also been performed. Comparison of the two versions of the mechanism highlights the superior performances of the one manufactured via FDM-CFRT in terms of weight, motor torque requirements and motion precision.

In this work, we present a novel concept of adaptive friction damper based on electrostatic adhesion and we characterize its performance under quasi-static conditions. The concept is based on a stack of circular electrodes structurally coupled to different ends of the damper, separated by a thin dielectric film and hinged around a common axle. When an electric potential is applied, the electrodes experience an attractive force, which is used to control the transfer of shear stress between electrodes and thus the resistive torque of the assembly and the amount of energy dissipated. However, imperfections on the contact surfaces and air gaps have a strong detrimental effect on the resistive torque. A prototype of the damper was manufactured and the resistive torque was measured as a function of applied voltage. Theoretical and experimental results were compared to estimate the average thickness of the air gap. The surface roughness of the electrodes and of the dielectric was measured before and after the mechanical test. Moreover, the surface of an entire electrode was scanned to measure its planarity. Then, the results were compared with the value of the air gap previously estimated. The maximum resistive torque measured was constant over five actuation cycles for constant values of the voltage applied and, as expected, increased quadratically with the voltage. The estimated value of the air gap amounted to 38 μm. Both the electrodes and the dielectric showed an increase in average surface roughness after the mechanical test; however, the surface roughness was lower than 1 μm in both cases and could not justify the estimated air gap. On the other hand, we observed a large inhomogeneity in the planarity of the electrode, which was comparable with the thickness of the air gap previously estimated. The results obtained demonstrated the possibility to adapt the resistive torque of the damper using an electrical input and proved the feasibility of the concept. Further work has to focus on the design of the electrodes and on the operating life of the damper. We envisage that the concept could replace traditional, semi-active dampers in automotive or in aerospace applications.

Structural instability, in particular postbuckling resulted in predefined constraints, has been performing advantages in many applications given their promising mechanical characteristics. However, inadequate studies have been conducted to effectively control and tune the postbuckling behavior of bilaterally constrained nonuniform beams. This study develops postbuckling systems comprised of multiple nonuniform beams subjected to bilateral confinements. Theoretical model is developed using Euler-Bernoulli theory and small deformation assumptions to predict postbuckling response of the beam systems under quasi-static axial loading. To locate the minimum energy path of the deformed beam system, the minimization problem of total potential energies of the bi-walled beam systems is solved by Nelder-Mead algorithm. Snap-through transitions of buckled systems are shown by drops in the response curves. To validate the developed model with existing models in literature, the model was simplified to account for single uniform beam under displacement control. The proposed model is experimentally and numerically validated, and satisfactory agreements are obtained. Parametric studies are carried out to investigate the influence of varying the geometric parameters (i.e., length, thickness) of the nonuniform beams on the tunable systems. Using the presented theoretical model, the postbuckling events can be accurately controlled by the geometry properties of the nonuniform beams.

The SALUTE project aims at evaluating performance of metacomposites for acoustic smart lining in grazing turbulent flow. Theoretical and numerical investigations are carried out for designing innovative specimen. A specific focus is placed in the realization of prototypes for evaluating the metacomposite liner performances in 2D and 3D liners, its process complexity and robustness. The insight gain in this project is new tools for obtaining innovative samples; the acoustical experimental tests demonstrate efficiency and robustness of such technology for controlling UHBR noise emission. This paper is focused on parametric study based on the maximization of the absorption coefficient in a duct by optimizing the impedance of a treated area.

Multifunctional Structures for Attitude Control (MSAC) is a new spacecraft attitude control system that utilizes deployable panels as multifunctional intelligent structures to provide both fine pointing and large slew attitude control. Previous studies introduced MSAC design and operation concepts, simulation-based design studies, and Hardware-in-the-Loop (HIL) validation of a simplified prototype. In this article, we expand the scope of design studies to include individual compliant piezo-electric actuators and associated power electronics. This advance is a step toward high-fidelity MSAC system operation, and reveals new design insights for further performance enhancement. Actuators are designed using pseudo rigid body dynamic models (PRBDMs), and are validated for steady-state and step responses against Finite Element Analysis. The drive electronics model consists of a few distinct topologies that will be used to evaluate system performance for given mechanical and control system designs. Subsequently, a high-fidelity multiphysics multibody MSAC system model, based on the validated compliant actuators and drive electronics, is developed to support implementation of MSAC Control Co-design optimization studies. This model will be used to demonstrate the impact of including the power electronics design in the Optimal Control Co-Design domain. The different control trajectories are compared for slew rates and the vibrational jitter introduced to the satellite. The results from this work will be used to realize closed-loop control trajectories that have minimal jitter introduction while providing high slew rates.

3D printing technologies have advanced significantly in recent years allowing for additive manufacturing of new structured materials, expanding the range, function, and capabilities of manufactured components. In this work, flexible capacitors were produced using additive manufacturing and compared to commercially available capacitance sensors in strain testing. The sensors utilize thermoplastic polyurethane (TPU) printed using fused filament fabrication methods as a dielectric substrate and a combination of flexible inks for production of the conductive surface. Flexible inks were printed using syringe based deposition methods on a custom designed printer using the TPU substrate. Results demonstrated successful capacitor production with capacitance values ranging from 2–70 pF depending on geometry, material, and printing conditions. The 3D printed flexible capacitors were characterized over a frequency range of 100 Hz to 10 kHz and compared to commercial roll-to-roll produced capacitors. Strain testing was conducted from 0–50% strain using a mechanical testing machine for the range of sensors and final capacitance post strain was measured to calculate deviation from original capacitance values. The sensors exhibited a relatively linear increase in capacitance when strained and returned to a resting position upon release of strain with minimal hysteresis effects, demonstrating their utility as 3D printed sensors.

This paper presents a novel shape memory alloy (SMA) valve actuator concept for active venting in injection molding applications. The developed system can be used to expel air which is trapped during the injection molding process. If such air bubbles are not properly removed from the cavity, they would result into an uncomplete cast and, in turn, in an unsuccessful molding. To address this issue, we propose a new valve system based on an agonist-antagonist SMA-spring actuator concept. By means of the developed SMA valve, the same dynamic performance of conventional actuators can be achieved with a more compact and lightweight actuator design. Design process, assembly, and validation of the novel SMA actuator are first described. In addition, development of an electronics concept and a test rig is discussed. First validation results are finally presented, showing the prototype electro-mechanical response when operating at different ambient temperatures.

This paper reports on the design and optimization of different types of piezoelectric actuators for aeroacoustic control applications. This study was carried out within the context of the European project CleanSky 2/InnoSTAT. The aim of our work is to reduce the aeroacoustic noises that appear in an airplane turbofan by adding an area of piezoelectric actuators on the Outlet Guide Vanes (OGV). These piezoelectric structures will subsequently be controlled with an active approach and tested in the open-jet anechoic wind tunnel at LMFE. The noise source which has to be reduce/control comes from vortices located in the turbulent flow (which can for example be created by the fan module) interacting with the stator blades. The predominant frequencies and the pressure fluctuations levels related to these vortices rely on the airflow speed and are fixed between 1000Hz and 2000Hz in our case. To reach the target, we plan to manufacture an area of piezoelectric actuators on the intrados and the extrados of the stator blades in order to control the response of the blade to the turbulence of the airflow responsible for the aeroacoustic noise. Several adjacent blades will be equipped with this type of transducers. This study outline the design and the optimization of each piezoelectric cell in order to achieve good results in the frequency range previously defined as well as an acceptable mechanical strength of the blade. A most detailed study on the active shunt will be investigate later on.

Locally resonant metamaterials have attracted lots of research interests for the application of vibration suppression which is a fundamental problem but remains a big challenge in the engineering field. The transverse wave propagation in a beam is through the transmission of the shear force and bending moment. Most designs of metamaterials in the existing literature exploit translational local resonators to induce reaction force to prevent the transmission of the shear force, hence the wave propagation. This paper studies a metamaterial beam attached with torsional local resonators. The reaction moments generated by the torsional resonators are expected to neutralize the bending moment in the beam, thus preventing the wave propagation. The existence of torsional resonators leads to the moment discontinuity conditions which cannot be directly taken into account using the Euler beam theory. Based on the Timoshenko beam theory, the band structure analysis is developed through a modal analysis based on the infinite periodic local resonator structure. The numerical results reveal that the locally resonant frequency corresponds to the upper bound of the band gap. Both infinitely long and finitely long beams are also modeled using finite element method. The transmittance is calculated to verify the band structure analysis.

3D printed flexible sensors have demonstrated great potential for utilization in a variety of different applications including healthcare, environmental sensing, and industrial applications. In recent years, research on this topic has increased to meet low-cost sensing needs due to the development of innovative materials and printing techniques that reduce cost, production time, and enhance the electrical and mechanical properties of the sensors. This paper presents computational simulations of 3D printed flexible sensors, capable of producing an output signal based on the deformation caused by external forces. Two different sensors were designed and tested, working based on a capacitance and resistance change produced by structural deformation. The capacitance sensor was designed maximizing the area of the electrodes and distributing the electrodes over a flexible membrane taking advantage of the produced deformation to reduce the distance between the electrodes. The reduction in the distance between the electrodes increases the capacitance value of the structure. The capacitance sensor was able to almost triple its baseline capacitance when 30 kPa of pressure was applied. The resistance sensor was designed with one continuous flexible conductive element attached to a flexible membrane, taking advantage of the distortion induced in the conductive element. The deformation in the conductive element increases the length of the resistor and causes the resistance value of the structure to increase. The resistance sensor was able to increase its resistance by 1200 ω with 30 kPa of applied pressure. Finally, preliminary results of 3D printed sensors were demonstrated.

Shape memory alloys (SMAs) are a well-known class of smart materials which allow the design of compact and silent actuation mechanisms. A remarkable feature of SMAs is self-sensing, namely the possibility to reconstruct the actuator position information from electrical resistance measurements. In case of simple SMA actuators, such as spring-loaded wires, the relation between resistance and displacement is usually linear and thus simple to exploit for self-sensing. For more advanced actuator types, such as protagonist-antagonist SMA configurations, the resistance-displacement characteristic is often hysteretic and thus more difficult to invert in real-time. To deal with this issue, this work proposes a novel self-sensing method for protagonist-antagonist SMA actuators having a highly hysteretic resistance-displacement behavior. An online hysteresis compensation scheme, based on the modified Prandtl-Ishlinskii model, is implemented and used to linearize the resistance-displacement characteristic. A lab setup which allows characterization of antagonistic SMA system as well as implementation of self-sensing control architectures is also developed. Experimental results show how, when combined with a PI controller, the developed scheme permits to noticeably reduce the error in comparison to compensator-free self-sensing architectures.

In order to increase precision and productivity in production systems, active components are increasingly being used which operate on the basis of conventional principles such as electrodynamics, hydraulics or pneumatics. An increasing performance range leads to larger demands in terms of function and energy density, which conventional actuators can only fulfil to a limited extent. Thermal shape memory alloys are the basis of an actuator technology that can overcome these challenges, but have recently been researched and used mainly as wire actuators. The associated drawbacks regarding realizable forces and large installation space may be the reasons why shape memory alloys have not yet been established in the field of production technology. This paper presents an alternative form of using shape memory alloys, which makes it possible to realize significantly higher energy densities. Starting from specific use cases, the basic design is discussed and a developed design methodology for such actuators is presented. This methodology is validated by measurements. Finally, an exemplary actuator concept is presented.

The piezoresistive effect in conductive nanofiller-modified polymer, cementitious, and ceramic composites has immense potential to enable multifunctional properties such as intrinsic self-sensing. To date, much work has been done to study the piezoresistive effect under quasi-static loading. Some work has also been done to study the piezoresistive effect under cyclic loading such as when a piezoresistive patch is adhered directly to an oscillating substrate. However, little-to-no work has been done with regard to general dynamic loading conditions such as strain waves originating from a remote source. This is an important gap in the state of the art for two reasons: One, coupling the self-sensing nature of nanocomposites with general elastodynamics is a possible pathway to enabling the study of full-field dynamics (i.e. using the piezoresistive effect to study internal dynamics as opposed to just surface measurements available via tools such as accelerometers and laser vibrometry). And two, coupling piezoresistive self-sensing with damage detection via vibratory methods could lead to transformative gains in the areas of structural health monitoring (SHM) and nondestructive evaluation (NDE). Therefore, we herein work towards addressing this gap in the state of the art by developing basic knowledge on the relation between elastic strain waves and piezoresistive response. Specifically, an electromagnetic-piezoelectric shaker is used to inject highly-controlled strain waves into a long and slender carbon nanofiber (CNF)-modified epoxy rod. Resistance changes along the length of the rod are then measured as strain waves travel along the length of the rod. It is shown that the measured resistance response closely matches the applied mechanical loading. Results from this preliminary study suggest the establishment of an exciting new field — piezoresistive elastodynamics.

Bistable composites have created much attention in engineering applications because of its ability to sustain two stable shapes. A systematic layup of carbon fiber reinforced polymer (CFRP) causes bistability in a lamina. The transition from one stable shape to another is occurred by snap-through and snap-back process. Due to their adaptive nature a lot of study has been conducted on a 2D laminate for over the past 30 years. However, fabrication of a 3D model that exhibits bistability is yet to be explored. In this research we fabricated a 3D bistable composite structure having two parallel cross-ply square laminates connected by a rigid tab at one edge. The entire structure exhibits bistability when the two laminates are actuated simultaneously. The parallel laminates are also independent when actuated individually, making the model achieve four independent stable shapes. Our goal is to understand the bistable behavior and predict the degree of curvature and the snap through response of the solid structure. This paper discusses the fabrication of a solid composite structure that can be further analyzed numerically by creating an FEA model using ABAQUS. The simulation results could be validated experimentally. In this research we also aim to put together an analytical model of this 3D laminate structure. Successful fabrication and mathematical analysis of our 3D laminate using carbon fiber reinforced polymer will hopefully inspire additive manufacturing of bistable composite structure that will lead to more complicated design of bistable materials with more morphing characteristics.

Alternating voltage is available in many environments for actuators. Due to the fact that a lot of actuators cannot directly handle this type of supply voltage, such as shape memory alloy (SMA) actuators, the voltage is usually converted to direct current. In the case of SMA actuators, the supply voltage often even has to be adjusted to the electrical resistance of each particular actuator. Due to high energy potential in AC supplies, conventional activation for SMA actuators over several seconds is not possible. In this study a control procedure for SMA wire actuators with high AC voltage supply is presented, which allows very flexible and versatile control of SMA wires. In addition two different types of activation are distinguished in an experimental study: one-time activation and activation over a longer period of time. The objective of the one-time activation is to reach a given actuator displacement. The activation over time is intended to hold a given position. The results of this series of experiments are presented and the resulting energy saving potential in high voltage SMA activation is observed.