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.

Helicopters suffer from a number of problems raised from the high vibratory loads, noise generation, load capacity limitations, forward speed limitation etc. Especially unsteady aerodynamic conditions due to the different aerodynamic environment between advised and retreating side of the rotor cause most of these problems. Researchers study on passive and active methods to eliminate negative effects of aerodynamic loads. Nowadays, active methods such as Higher Harmonic Control (HHC), Individual Blade Control (IBC), Active Control of Structural Response (ACSR), Active Twist Blade (ATB), and Active Trailing-edge Flap (ATF) gain importance to vibration and noise reduction. In this paper, strain-induced blade twist control is studied integrated by Macro Fiber Composite (MFC) actuator. 3D model is presented to analyze the twisting of a morph and bimorph helicopter rotor blade comprising MFC actuator which is generally applied vibration suppression, shape control and health monitoring. The helicopter rotor blade is modeling with NACA23012 airfoil type and consists of D-spar made of unidirectional fiberglass, ±45° Glass Fiber Reinforced Polymer (GFRP) and foam core. Two-way fluid-structure interaction (FSI) method is used to simulate loop between fluid flow and physical structure to enable the behavior of the complex system. To develop piezoelectric effects, thermal strain analogy based on the similarities between thermal and piezo strains. The optimization results are obtained to show the influence of different design parameters such as web length, spar circular fitting, MFC chord length on active twist control. Also, skin thickness, spar thickness, web thickness are used to optimization parameters to illustrate effects on torsion angle by applying response surface methodology. Selection of correct design parameters can then be determined based on this system results.

The adaptation of a wing contour is important for most aircraft, because of the different flight states. That’s why an enormous number of mechanisms exists and reaches from conventional slats and flaps to morphing mechanisms, which are integrated in the wing. Especially integrated mechanisms reduce the number of gaps at the wing skin and produce less turbulent flow. However these concepts are located at a certain section of the wing. This leads to morphing and fixed wing sections, which are located next to each other. Commonly, the transition between these sections is not designed or a wing fence is used. If the transition is not designed, the wing has a step with an activated morphing mechanism and that produces additional vortices. A new skin design will be presented in order to smooth the contour between a fixed wing and a morphing wing. Here the transition between a droop nose and a fixed wing is considered. The skin material is a mix of ethylene propylene diene monomer rubber and glass-fiber reinforced plastic. The rubber is the baseline material, while the glass-fiber is added as stripes in chord-wise direction. In span-wise direction the glass fiber is connected with the rubber. The rubber carries the loads in span-wise direction and reduces the required actuation force. The glass fiber stiffens the skin locally in chord wise direction and keeps the basic contour of the skin. Some geometrical parameters within the skin layup can be varied to change the transition along the span or to reduce the maximum strain within the skin. The local strain maximum is a result of the material transition with different modules. One design of a leading edge was manufactured with an existing mold and it has a span of 200 mm. There are two essential aspects from a structural point of view. One is a nearly continuous deformation along the span and the second is the maximum strain in the rubber. Both aspects are investigated in an experiment and the results are compared with a simulation model. The results show a reliable concept and its numerical model, which will be assigned to a full scale demonstrator. This demonstrator will have a span of 1000 mm and will show the smooth skin transition between a droop nose and a fixed wing.

The main goal of this study is the optimization of vibration reduction on helicopter blade by using macro fiber composite (MFC) actuator under pressure loading. Due to unsteady aerodynamic conditions, vibration occurs mainly on the rotor blade during forward flight and hover. High level of vibration effects fatigue life of components, flight envelope, pleasant for passengers and crew. In this study, the vibration reduction phenomenon on helicopter blade is investigated. 3D helicopter blade model is used to perform the aeroelastic behavior of a helicopter blade. Blade design is created by Spaceclaim and finite element analysis is conducted by ANSYS 19.0. Generated model are solved via Fluent by using two-way fluid-solid coupling analysis, then the analyzed results (all aerodynamic loads) are directly transferred to the structural model. Mechanical results (displacement etc.) are also handed over to the Fluent analysis by helping fluid-structure interaction interface. Modal and harmonic analysis are performed after FSI analysis. Shark 120 unmanned helicopter blade model is used with NACA 23012 airfoil. The baseline of the blade structure consists of D spar made of unidirectional Glass Fiber Reinforced Polymer +45°/−45° GFRP skin. MFC, which was developed by NASA’s Langley Research Center for the shaping of aerospace structures, is applied on both upper and lower surfaces of the blade to reduce the amplitude in the twist mode resonant frequency. D33 effect is important for elongation and to observe twist motion. To foresee the behavior of the MFC, thermo-elasticity analogy approach is applied to the model. Therefore, piezoelectric voltage actuation is applied as a temperature change on ANSYS. The thermal analogy is validated by using static behavior of cantilever beam with distributed induced strain actuators. Results for cantilever beam are compared to experimental results and ADINA code results existing in the literature. The effects of fiber orientation of MFC actuator and applied voltage on vibration reduction on helicopter blade are represented. The study shows that torsion mode determines the optimum placement of actuators. Fiber orientation of the MFC has few and limited influences on results. Additionally, the voltage applied on MFC has strong effects on the results and they must be selected according to applied model.

Glass Fiber Reinforced Polymer (GFRP) beams have shown over a 20% decrease in weight compared to more traditional materials without affecting system performance or fatigue life. These beams are being studied for use in automobile leaf-spring suspension systems to reduce the overall weight of the car therefore increasing fuel efficiency. These systems are subject to large amplitude mechanical vibrations at relatively constant frequencies, making them an ideal location for potential energy scavenging applications. This study analyses the effect on performance of GFRP beams by substituting various composite layers with piezoelectric fiber layers and the results on deflection and stiffness. Maximum deflection and stress in the beam is calculated for varying the piezoelectric fiber layer within the beam. Initial simulations of a simply supported multimorph beam were run in ABAQUS/CAE. The beam was designed with symmetric piezoelectric layers sandwiching a layer of S2-glass fiber reinforced polymer and modeled after traditional mono leaf-spring suspension designs with total dimensions 1480 × 72 × 37 mm 3 , with 27 mm camber. Both piezoelectric and GFRP layers had the same dimensions and initially were assumed to have non-directional bulk behavior. The loading of the beam was chosen to resemble loading of a leaf spring, corresponding to the stresses required to cycle the leaf at a stress ratio between R = 0.2 and 0.4, common values in heavy-duty suspension fatigue analysis. The maximum stresses accounted for are based on the monotonic load required to set the bottom leaf surface under tension. These results were then used in a fiber orientation optimization algorithm in Matlab. Analysis was conducted on a general stacking sequence [0°/45°] s , and stress distributions for cross ply [0°/90°] s , and angle ply [+45°/−45°] s were examined. Fiber orientation was optimized for both the glass fiber reinforced polymer layer to maximize stiffness, and the piezoelectric fiber layers to simultaneously minimize the effect on stiffness while minimizing deflection. Likewise, these fibers could be activated through the application of electric field to increase or decrease the stiffness of the beam. The optimal fiber orientation was then imported back into the ABAQUS/CAE model for a refined simulation taking into account the effects of fiber orientation on each layer.

The dynamic behavior of sandwich composite structures needs to be predicted as accurately as possible for ensuring safety and serviceability. A properly converged finite element model can accurately predict such behavior, if the current material properties are determined within very close ranges to their actual values. The initial nominal values of material properties are guessed from established standards or from manufacturer’s data, followed by verification through quasi-static characterization tests of extracted samples. Such structures can be modal tested to determine the dynamic responses very accurately, as and when required. A mathematically well posed inverse problem can thus be formulated to inversely update the material parameters accurately from initial guesses through finite element model updating procedures. Such exercise can be conveniently used for condition assessment and health monitoring of sandwich composite structures. The method is capable of determining the degradation of material properties, hence suitable for damage detection. The in-plane as well as out-of-plane elastic moduli can be determined to predict the actual responses which can be verified by physical measurement. In the present investigation, the in-plane and out-of-plane elastic parameters of the face sheets made of glass fiber reinforced plastics, i.e. E 1 , E 2 , G 12 , G 13 , G 23 of the face sheet and the Young’s modulus (E) of the core of a sandwich composite plate has been determined inversely from available modal responses. The method is based on the correlation between the dynamic responses as predicted using finite element model and those measured from modal testing to form the objective function, sensitive enough to the in-plane and out-of-plane material constants. A gradient based Inverse Eigensensivity Method (IEM) has been implemented to identify these material parameters of a rectangular sandwich composite plate from natural frequencies. It may be noted that the initial characterization test data may not be useful in predicting accurate dynamic responses of existing degraded sandwich structures, if the material constants have changed substantially. Destructive characterization test on existing structure is mostly not permitted as samples need to be extracted which may damage the otherwise intact structure.

Morphing is a technology with high potential to reduce emissions in aviation by adapting the shape of the wings to varying external operating conditions. This paper is presenting results from the EU FP7 funded CHANGE project, where different concepts to adapt a UAV wing airfoil to different demands were investigated. The paper is concentrating on the design and experimental testing of a droop nose, which transforms the leading edge part of the 60 cm chord airfoil from a NACA 6510 shape for loiter and low speed to a NACA 2510 shape for a high speed mission. This paper is presenting the use of an especially soft skin, which reduces the needed force for morphing. That way the requirements for the servos driving the droop nose could be reduced significantly. This paper is showing the implications of such a soft design on the accuracy of the shape generated. For such a skin design, the driving mechanism of the system is designed as a compliant mechanism, which was generated by topology optimization, taking into account aerodynamic loads. For easy manufacturing reasons, thermoplastic polylactic acid (PLA) with zero warp property was used for the manufacturing of this compliant mechanism. Finally deformation measurements of the morphing skin were carried out in a series of lab tests. The match between measured and numerically derived section is quite good, especially in the root region of the wing. Finally an example of an alternative concept to the soft approach is presented. It is the metal based compliant mechanism with a rather stiff GFRP skin. A discussion on the use of different materials and the way forward towards 3D skin optimization is wrapping up the paper.

Morphing is a technology with high potential to reduce emissions in aviation, since it enables wings to adapt their shape to operate at a higher efficiency over the full range of flight conditions. This paper is presenting a concept to adapt camber by drooping the nose. The scope is the setup and bench top testing of a full scale wing tip leading edge wind tunnel model with a morphing droop nose. The complete model features a span of 1.3 m and a strong taper from the root to the tip. For completeness, the design approach is covered as well. The design comprises a GFRP skin to be drooped by two compliant mechanisms, which are driven by linear motors. The compliant morphing devices are “designed-through-optimization”, with the optimization algorithms including Simplex optimization for composite compliant skin design, continuum-based and load path representation topology optimization methods for compliant internal substructure design. The compliant mechanism is manufactured by nickel-titanium alloy to allow high strains in the order of several percent, which is shown to be critical in the design of such compliant mechanisms. In order to validate the models, strains within the mechanisms are measured while drooping the nose in the bench top test. This is done after installing the mechanisms into the leading edge skin. It can be shown, that the simulation for the inboard mechanism is close to the experimental results. The comparison of strain levels in the skin and in the mechanism during droop reveals that the stiffness distribution between these two components is quite different. As a result this ratio can be taken into account in future design processes in order to distribute strains more evenly. Moreover the 3D shapes of the morphed and clean skin are measured and their comparison with the target shapes is presented as well. Finally, the bench top tests are a proof of concept for the overall concept and design which resultes in a “go” for the following low speed subsonic wind tunnel tests.

Utilizing conductivity changes to locate matrix damage in glass fiber reinforced polymers (GFRPs) manufactured with nanocomposite matrices is a promising avenue of composite structural health monitoring (SHM) with the potential to ensure unprecedented levels of safety. Nanocomposites depend on the formation of well-connected nanofiller networks for electrical conductivity. Therefore, matrix damage that severs the connection between nanofillers will manifest as a local change in conductivity. This research advances state of the art conductivity-based SHM by employing electrical impedance tomography (EIT) to locate damage-induced conductivity changes in a glass fiber/epoxy laminate manufactured with carbon black (CB) filler. EIT for damage detection is characterized by identifying the lower threshold of through-hole detection and demonstrating the capability of EIT to accurately resolve multiple through holes. It is found that through holes as small as 3.18 mm in diameter can be detected, and EIT can detect multiple through holes. However, sensitivity to new through holes is diminished in the presence of existing through holes unless a damaged baseline is used. These research findings demonstrate the considerable potential of conductivity-based health monitoring for GFRP laminates with conductive networks of nanoparticles in the matrix.

A concept for a novel folding wing is presented, which, using the Brazier effect, can snap from a stable, extended position to a folded configuration. A wing typical of size used in an unmanned aircraft vehicle (UAV) is examined, including manufacturing aspects as well as an analytical and a finite element model (FEM) of the structure. The wing is simply made of a glass fiber reinforced plastic (GFRP) skin stiffened by ribs at regular intervals. At the mid-span location, a cut-out is made in the leading and trailing edge in order to allow the pressure and suction sides of the wing to collapse inward when folding occurs (due to Brazier effect). The analytical model draws upon work from Brazier to predict the maximum bending moment the folding section can withstand before buckling. A FEM, using a quasi-static analysis and requiring a contact definition to allow the wing surfaces to meet, reproduces with accuracy the folding pattern seen on the prototype. A bending test of the demonstrator confirmed the validity of the models in terms of bending stiffness, bending snap through and folding radius of curvature.

In this paper we describe extensions and improvements upon prior work on “active cells” — small contractile electromechanical elements used in large numbers to create actuated composite structures. Each element (cell) consists of square fiberglass end-pieces encapsulating a bias spring within two telescoping tubes, actuated using two contractile shape memory coils, and occupying approx. 1cm 3 when fully contracted. The end-pieces contain conductive interfaces to nearby cells, thus allowing channeling of power through a connected network of cells to provide actuation far from the source of electrical current. Prior work developed the conceptual structure of such a cell as well as preliminary prototypes. This paper describes the attachment of cells to each other and to rapid-prototyped cell interconnects — as well as improved fabrication techniques for the shape-memory coils — resulting in robust actuation for each cell, and the creation of considerably more complex chained and networked composite structures. A detailed exploration of appropriate interconnect mechanisms, powering schemes to provide network-level structural deformations, and examples of multi-cell structures are presented.

The trend towards higher reliance on fiber-reinforced composites for structural components has led to the need to rethink current nondestructive evaluation (NDE) strategies. In principle, embeddable sensor schemes are desired for green-light/red-light structural health monitoring systems that do not negatively affect the properties and performance of the host structure. However, there are still numerous challenges that need to be overcome before these embedded sensing technologies can be realized for real-world structural systems. For example, some of these issues and challenges include the damage detection sensitivity/threshold, reliability of the system, transportability of the system to multiple configurations and different types of structural components, and signal processing/interpretation. The objective of this study is to develop a novel, embedded sensing system that can accurately quantify damage to composites without interfering with structural performance and functionality. In particular, this study will utilize multi-walled carbon nanotube (MWNT)-polyelectrolyte (PE) thin films deposited on a glass fiber substrate for in situ composite structural monitoring. A layer-by-layer (LbL) film fabrication methodology is employed for depositing piezoresistive nanocomposites directly onto glass fiber fabrics, and the resulting film exhibits excellent strain sensing performance, homogeneity, and exhibits no phase segregation. Specifically, the LbL fabrication process will employ polycationic poly(vinyl alcohol) (PVA) and polyanionic poly(sodium 4-styrene sulfonate) (PSS) doped with MWNTs for fabricating the electrically-conductive and piezoresistive thin films. Upon film deposition, the glass fiber substrates are infused with an epoxy matrix via wet-layup to fabricate self-sensing glass fiber-reinforced polymer (GFRP) composite specimens for testing. A frequency-domain approach, based on electrical impedance spectroscopy, is used to characterize the electromechanical response of the GFRP-MWNT-based thin film samples when subjected to complex uni-axial tensile load patterns. A resistor connected to a parallel resistor-capacitor circuit model is proposed for fitting experimental impedance spectroscopic measurements. It has been found that the series resistor models the bulk thin film piezoresistive performance accurately. In addition, these impedance measurements shed light on the glass fiber-thin film interaction electromechanical behavior. Bi-functional strain sensitivity is observed for all GFRP specimens, and the transition point of bilinear strain sensitivity is utilized as a possible metric for GFRP damage detection.

Artificial or “bionic” limbs have been the subject of considerable research, TV shows, and dreams by children. The “Six Million Dollar Man” show was about a man who received artificial limbs after his own were lost in an accident. To get students interested in practical engineering, the current work showcases a simple artificial arm that produces greater force than a typical man, demonstrates the capability of Rubber Muscle Actuators (RMA), and provides a portable “arm wrestling platform” for student recruitment efforts. The actuators for “Kingsville Arm One & Two” are McKibben-like actuators made from fiber-reinforced elastomeric composites. These actuators offer excellent strength-to-weight ratios and contract similar to a human muscle. RMAs produce greater force and have less “blow-outs” than typical McKibben actuators because of optimized braid angles and ends that transfer loads through the braid fibers. Kingsville Arm One (KA1) was developed in just two weeks. It consisted of carbon/fiberglass/epoxy composite tubular bones, a metal clevis “elbow” and four RMAs. With considerable effort, a very large student was able to overcome the force generated in an “arm wrestling” contest. KA1’s actuators had end attachments that transferred loads well and enabled flexibility, but easily tore and had air leaks. Kingsville Arm Two (KA2) had new “bones” and RMAs. Although slightly smaller diameters, the KA2 RMAs produced comparable forces to the KA1 RMAs and had molded end attachments. The rigid ends did not allow as much rotation as expected and necessitated using just 2 RMAs. With only two RMAs, KA2 produced approximately the same “arm strength” as KA1. Future work will focus on flexible but durable RMA molded ends, life-like skins and a realistic “hand.”

Laminates that exhibit high and negative Poisson’s ratios can be used as solid-state actuators, passive and active vibration dampers, and for morphing aircraft structures. Recently, fiber-reinforced elastomer (FRE) laminates have been fabricated that exhibit extreme (high and negative) Poisson’s ratios [1]. The current research explores twisted fiber bundle elastomeric laminates (both single and double helix) which are being investigated using experimentation, linear and non-linear finite element analysis (FEA). Twisted fiber bundles can be made from carbon fibers, fiberglass, etc, but for simplicity the current work uses twisted cotton string. It is observed that uniaxial fiber-reinforced elastomer laminates, where the fibers are twisted as shown in Figure 1, exhibit stress stiffening. Negative Poisson’s ratios may be produced if the fiber bundles have a double helical path as simulated by a series of laminated tubes. Future auxetic FRE laminates may be developed that do experience extreme shear.