This study presents and examines the concept of flexible skins for morphing aircraft applications comprising a cellular honeycomb core covered by compliant face-sheet. The overall properties are then largely governed characteristics core, which in turn dependent on cell parameters. results this showed that cores could easily undergo global strains over 10 times greater than virgin material they were built. in-plane stiffness is generally several orders magnitude lower material. Using thicker...

Cellular honeycomb cores with overlying flexible face sheets have been proposed for use as flex skins morphing aircraft. The cellular cores, which provide underlying support to the carrying aerodynamic loads, must low in-plane stiffness and high strain capability. For one-dimensional applications such span-, chord-, or camber-change, restraining Poisson’s contraction (or bulging) that a conventional core would otherwise experience in non-morphing direction results substantial increase...

This paper identifies the desirable attributes of a flexible skin morphing wing. The study is conducted using airfoil camber as an example. ideal flex-skin would be highly anisotropic, having low in-plane axial stiffness but high out-of-plane flexural stiffness. Reduced allows at actuation cost. However, for some substructure and designs, lower limit on skin's may required to prevent unacceptable global deformation under aerodynamic loads. High prevents local sections between supports due...

Data from comprehensive thermomechanical tests of shape memory polymers are reported, with specimens tested up to 75% strain and between 30—120°C temperatures. The data is analyzed key observations drawn. stress/strain behavior during loading at temperatures above glass transition for the Veriflex TM polymer was linear did not show much variation actual temperature. When cooled end constraints, thermally-induced tensile stresses developed, but only after temperature reduced below material...

This paper describes a method to vary the flexural bending stiffness of multi-layered beam. The beam comprises base layer with polymer layers on upper and lower surfaces, stiff cover layers. Flexural variation is based concept that when stiff, are strongly coupled entire bends as an integral unit. In effect, we have 'thick' contributions from all stiffness. On other hand, if shear modulus reduced, undergoes bending, largely decoupled base, overall correspondingly reduces. reduced by...

Morphing aircraft wings require flexible skins that undergo large strains, have low in-plane stiffness, and high out-of-plane stiffness to carry aerodynamic loads. For some morphing applications deformation in the flexskin is required one direction. In these cases, a matrix composite (FMC) skin proposed as possible solution. A FMC comprises of stiff fibers embedded soft, high-strain capable material. The matrix-dominated direction aligned with This allows strain at energy cost. However,...

Chord extension morphing of helicopter rotors has recently been shown to be highly beneficial for stall alleviation, with the ability reduce power near envelope boundaries and increase maximum gross weight, altitude, speed capability aircraft. This article presents a mechanism extend chord section rotor blade. The region aft leading-edge spar contains cellular structure. In compact state, edge structure aligns trailing rest When is in extended that blade increased by 30%. transitioning from...

The pseudoelastic stress/strain hysteresis behavior observed in nickel-titanium (Ni-Ti) shape memory alloys (SMAs) above the austenite finish temperature can be exploited to provide passive structural damping a variety of applications. present study characterizes Ni-Ti SMAs using complex modulus approach, commonly used dynamics for characterization materials. Results indicate that as excitation frequency increases, loss (a measure damping) undergoes rapid initial decrease. value (and...

This article focuses on flexskins comprising of a cellular substructure and pretensioned facesheet for shear morphing applications. The unit cell the is strand with some strain-relief feature, it supports segment facesheet. function feature to reduce peak strains in consequently actuation work during morphing. Central hexagonal cells, elliptical half cells provided sought strain relief at edges strand, but sharp corners proximity these central features those from adjacent strands led...

Morphing aircraft wings require flexible skins that can undergo large strains, have low in-plane stiffness and very high out-of-plane flexural bending stiffness. The strain capability is especially important for gross morphing applications such as span change where the may be required to axial strains of order 50% or greater. Low allows accomplished at a reasonable energy cost while ensures skin sections between supports do not suffer from significant deformation under aerodynamic pressure...

This article examines the bistable behavior of an arch for morphing applications. The has a cosine profile, is clamped at both ends, and restrained axially by spring one end. Fabrication testing several Delrin NiTiNOL specimens (with varying height, thickness, stiffness) were followed ANSYS finite element modeling, simulation results showed good overall agreement with test results. A parametric study was conducted using model to assess influence stiffness on behavior. indicated that lower...

An experimental investigation was conducted to determine the pseudoelastic hysteresis damping characteristics of Ni-Ti Shape Memory Alloy (SMA) wires. The comprehensive study examines effects cycling, oscillation frequency, strain amplitude, temperature, and static offset on stress-strain SMA wires under axial loading. Experimental data are obtained for complete austenite-martensite transformation as well partial hysteresis. results indicate that frequency excitation increases, reverse phase...

A conformable airfoil is proposed as an alternative to trailing-edge flaps used for active helicopter vibration reduction through high-frequency changes in camber. The design consists of several compliant mechanisms predetermined topology that are placed serially within the along chord, aft leading-edge spar. shape optimization approach mechanisms, which objective maximize deflection while minimizing deflections due aerodynamic loads. Solutions were obtained using a sequential linear...

This paper examines rotor power reductions achievable through a combination of radius and RPM variation. The study is based on utility helicopter similar to the UH-60A considers +17% –16% variation in ±11% about baseline, over range airspeed, gross weight, altitude. Results show that decreasing alone effectively reduced at cruise velocities low-and-light conditions, but diminished increasing altitude and/or low-speed flight. Increasing alone, other hand, had greatest effectiveness reduction...

This paper explores the feasibility of using Magnetorheological (MR) fluid-based dampers for lag damping augmentation in helicopters. An MR damper model is integrated with a rotor aeromechanical model. Two different control schemes are presented-namely On-Off scheme and Feedback Linearization scheme. In scheme, two criteria used to obtain equivalent linear nonlinear as function size perturbation applied field. The uses feedback controller linearize force output damper. compared transient...

A viscoelastic solid model, comprising of a combination linear and non-linear springs dashpots, is developed to represent an elastomeric damper. constitutive differential equation derived characterize the damper behaviour in time domain. system identification method presented determine spring - dashpot parameters (coefficients equation) from experimental data. The model able predict amplitude-dependent dampers under single as well dual-frequency excitations. `two-level implicit implicit'...

Structural grade materials with Young’s Modulus in the gigapascal range generally have very low damping, leading to requirement for auxiliary damping treatments many applications. This article examines whether a high and level can simultaneously be realized by introducing lossy polymeric infills into auxetic aluminum honeycombs. Using finite element analysis, honeycombs varying cell geometry infill stiffness, loaded x- y-directions, are examined. From results, it is observed that best...

In this study, lossy polymeric infills are introduced into metallic honeycombs with the goal that resulting filled simultaneously have high stiffness and appreciable loss factor. A finite element analysis is conducted honeycomb walls modeled beam elements infill shell elements. Soft (10 MPa) stiffer (100 fillers used, oriented to deform along x- y-directions. The article presents a discussion on cell geometries yield highest factor, for loading in two principle directions. When loaded,...

This paper focuses on the ability to introduce change in flexural bending stiffness of a niultilayered beam. The multilayered beam comprises base layer with polymer layers upper and lower surfaces stiff cover layers. can be reduced by effecting reduction shear modulus heating through glass transition. Stiffer strongly couple entire bends more as an integral unit On heating, results its undergoing deformation undergoes decoupling from reduces overall stiffness. A finite element analysis is...

Morphing aerospace structures could benefit from the ability of structural elements to transition a stiff load-bearing state relatively compliant that can undergo large deformation at low actuation cost. The present paper focuses on multi-layered beams with controllable flexural stiffness—comprising polymer layers affixed surfaces base beam and cover layers, in turn, layers. Heating through glass reduces its shear modulus, decouples overall stiffness. Although stiffness force required bend...