Journal of Intelligent Material Systems and Structures

A compact actuator to oscillate blade trailing-edge flap on a full-scale helicopter has been investigated for vibration suppression. The actuator consists of piezoelectric stacks and a dual-stage mechanical stroke amplifier. It is recommended that commercially available piezostack be used for timely manufacturing and maintenance rather than a custom-designed piezostack. An analytical approach to estimate the maximum actuator force requirement for the rotor in hover condition is discussed first. A piezostack down-selection through the experimental evaluation is presented, which is to select a piezostack with high stiffness as well as good strain/block force output among twelve commercial piezostacks. The design requirements of on-blade piezoelectric actuator are discussed, and one-dimensional stiffness modeling and finite element beam modeling are presented to evaluate the analytical/numerical actuator performance. The prototype actuator with a double-lever stroke amplifier was fabricated and tested on bench-top as well as in vacuum chamber. An amplification factor of 19.4 and the consistent actuator output up to 600 g of centrifugal loading were obtained. An improved actuator has been designed with a design refinement to reduce structural losses.

A new type of actuation device has been conceptualized that meets the needs of both large displacement force and bandwidth within a package more compact than the currently available magnetostrictive and stack-type piezoelectric actuators of similar rating. This concept relies on micro-scale electrohydrodynamic (EHD) pumping of a dielectric liquid within small channels. Configured as an actuator, the EHD pump(s) would be used to move fluid between two reservoirs—each having a compliant membrane that interfaces to the world to provide the means to achieve vibration cancellation or micro actuation.

Ordinarily limited to generating flow in macroscale applications, the EHD pump, when operating in a thermal induction mode, is shown to exhibit an exciting scaling law as its size is reduced. As the pump volume to surface area decreases, the energy going toward increasing pressure in the pump has an increasingly larger effect. Since the volume/surface area is proportional to 1/a, where a is the characteristic width or diameter of the channels comprising the pump, the pressure head generated scales similarly. Analytical and numerical studies have shown the EHD-pumped actuator to be capable of delivering equal force and bandwidth to magnetostrictive and stack-type piezo actuators, but with considerably greater displacement and a smaller size. Further, this type of actuator offers the possibility for deployment in active vibration control or micro actuation applications at significantly greater temperatures than for piezoelectric and magnetostrictive devices.

A novel approach has been developed for real-time characterization of a parachute during inflation. Two techniques were applied to measure static and dynamic stresses in a parachute canopy fabric material and suspension lines: the modal power distribution (MPD) technique and the fiber Bragg grating (FBG) technique. Several tests were conducted under various loading conditions, using a bi-axial tensile tester. The MPD technique was used to measure the transverse stresses in the parachute canopy fabric material and was applied using two experimental set-ups: one using a CCD camera and the other using a photo-detector. The FBG technique was used to measure the axial stresses in the parachute canopy fabric material. The tests were performed using the spectrum analyzer set-up with the bi-axial machine. Finally, a drop test was performed on the parachute canopy fabric material using the MPD technique with the photo-detector set-up.

An optimization method has been developed for design of compliant mechanical amplifiers for piezoceramic stack actuators. A topology optimization approach is used where the objective is to maximize the stroke amplification, and results show good algorithm convergence and good mechanism performance. The focus of this paper is on using the optimal topology solution to generate a solid model, and on improving the actuator performance through detail design and analysis of the resulting monolithic compliant mechanical amplifiers. A study of the effect of various flexure hinge configurations and other design parameters on the amplification and mechanical advantage of an actuator is performed. Another actuator with a large stroke amplification is designed using a batch of random starting points to the optimization algorithm. Prototype actuators have been fabricated, and the results of experimental validations are presented.

The thermally-induced deformations of multilayer disk-style benders that are consolidated at elevated temperature to cure the adhesives bonding the layers together and then cooled to room temperature are studied. Only axisymmetric deformations are considered, and hence the disks cool to a dome-like shape due to the different thermal expansion properties of the layers. The paper derives the equations governing the deformation and, since the out-of-plane deformations are often many times the disk thickness, geometrically nonlinear effects are considered in the derivation. As a comparison case, the equations are linearized and solved in closed form. The geometrically nonlinear case is solved by using the shooting method and the Rayleigh-Ritz method. A number of simple bender designs are studied to examine the influence of geometric nonlinearities, disk geometry, and layer material properties on the deformations. It is concluded that geometric nonlinearities lead to flattening of the dome relative to the geometrically linear case, and the thermally-induced deformations are sensitive to layer material properties, layer thickness, and disk radius.

A constitutive model and a finite element formulation are developed for predicting the thermomechanical response of SMA hybrid composite structures subjected to combined thermal and mechanical loads. The constitutive model is valid for constrained, restrained, or free recovery behavior with appropriate measurements of basic SMA material properties. The model captures the material nonlinearity of the SMA with temperature and more accurately captures the mechanics of composites with embedded SMA actuators as compared to other recently developed approaches. The constitutive and finite element models are amenable to commercial code implementation. The fundamental thermoelastic behavior of such structures is described in physical terms and related to the governing equations. It is shown that alloy selection is imperative for achieving the desired performance with respect to the application environment. It is also shown that fundamental efforts to strategically place actuators can produce dramatic performance improvements. Numerical results are shown for glass-epoxy beam specimens with embedded Nitinol actuators. Control of critical buckling temperature, thermal post-buckling deflection, and random response are demonstrated.

This paper presents the study of a field-controllable, semi-active magneto-rheological fluid (MRF) shock absorber for high-payload, off-highway vehicles. A MRF damper is developed that is tailored for ground vehicles which undergo a wide range of dynamic loading. The MRF damper also has the capability for different rebound and compression characteristics. The new MRF shock absorber emulates the original equipment manufacture shock absorber behavior in its passive-off mode. Theoretical and experimental studies are performed to examine this MRF damper. The Bingham Plastic theory is employed to model the nonlinear behavior of the MRF. A fluid-mechanics-based theoretical model along with a three-dimensional finite element electromagnetic analysis is utilized to predict the MRF damper performance. The theoretical and experimental results are demonstrated to be in good agreement.

This paper presents novel work on developing fiber optic micro-sensors and integrating them into soldiers’ uniforms. These fiber optic sensors can be used to sense various battlefield hazards in real-time, such as chemical and biological warfare threats, above-normal field temperatures, and other hazards. The developed fiber optic sensors use multifunctional materials as modified cladding materials, which can sense various environmental conditions. Appropriate materials can be chromogenic materials, chemical or biological agent, conducting polymer and others. The sensing function is based on their ability to change the light propagation characteristics of optical fibers.

Two types of materials, (1) thermochromic material, segmented polyurethane-diacetylene copolymer (SPU) [synthesized at the University of Akron (UA)], and (2) conducting polymer, polyaniline [synthesized at the University of Pennsylvania (U of P)], have been successfully used in this feasibility study to prove the concept of the design and development of the optical fiber sensors. Segmented polyurethane-diacetylene copolymer was selected as the thermochromic material for temperature sensor application. Polyaniline was chosen as the photo-chemical polymer for chemical sensor application. The developed methodology for building these sensors includes modifying the regular optical fibers, by replacing the fiber passive cladding with those sensitive materials. The integration of the sensory system into textile structures, done in collaboration with the North Carolina State University (NCSU), also showed good progress. An overview on the developed methodology and technical achievement is presented.