Structures For Space Applications Research Articles

Nonlinear vibration control effects of membrane structures with in-plane PVDF actuators: A parametric study

In recent years, with the increasing use of membrane structures in space applications, the problems of large-amplitude (compared to the thickness) vibrations arise; leading to the degradation of their working performance. It is challenging to control the large-amplitude vibrations of membranes due to the high flexibility, low damping, and strong geometrical nonlinearity. In this study, polyvinylidene fluoride (PVDF) actuators are considered to develop the active vibration control of a pre-tensioned Kapton membrane. The governing equations are established based on the geometrically nonlinear theory of plates, taking into account the modal control force induced by the actuators. To analyze the nonlinear dynamic characteristics of the membrane, the theoretical and approximate solutions of nonlinear frequencies of the membrane are obtained, and the discrepancies between the two solutions under different vibration amplitudes are discussed. Control performance for both free vibration and harmonic forced vibration of the membrane is numerically studied. A comprehensive parametric study is carried out to investigate the influences of different system parameters, including the pretension and the size of the membrane, and the position and number of the actuators, on the control performance. Analytical results indicate that the vibration of the membrane can be effectively suppressed with the appropriately laminated PVDF actuators. The results of this research can be extended to the active control of different gossamer space structures.

Створення та дослідження конструкцій перетворюваного обсягу космічного призначення

Створення та дослідження конструкцій перетворюваного обсягу космічного призначення

Active Vibration Suppression of an elastic piezoelectric sensor and actuator fitted cantilevered beam configurations as a generic smart composite structure

An efficient analytical method for vibration analysis of a Euler–Bernoulli beam with Spring Loading at the Tip has been developed as a baseline for treating flexible beam attached to central-body space structure, followed by the development of MATLAB© finite element method computational routine. Extension of this work is carried out for the generic problem of Active Vibration Suppression of a cantilevered Euler–Bernoulli beam with piezoelectric sensor and actuator attached as appropriate along the beam. Such generic example can be further extended for tackling light-weight structures in space applications, such as antennas, robot’s arms and solar panels. For comparative study, three generic configurations of the combined beam and piezoelectric elements are solved. The equation of motion of the beam is expressed using Hamilton’s principle, and the baseline problem is solved using Galerkin based finite element method. The robustness of the approach is assessed.

Fold-Resistant Characteristics of the Laminate Composites for Flexible Structure

There is considerable interest in the use of flexible laminate composite materials to improve the deployable structures for space applications. Critical to acceptance of these materials is the ability to achieve high packaging strains without damage. However, there does exist more or less damage during the process of folding and unfolding for the laminate composites. Better understanding of folding damage, therefore, is needed for the design of laminate composites and folding pattern. In this work we present a study on the fold-resistant characteristics of two different laminate composites, which were fabricated by covering the aramid fiber/epoxy and carbon fiber/epoxy prepregs respectively with polyimide film on both sides. The results of tensile tests on 3-layer structure laminate composites show that the fold-resistant properties of aramid fiber/epoxy composites could be improved with increasing of the resin content and decreasing of the fiber bundle diameter. For carbon fiber/epoxy composites, the effects of resin content and fiber bundle diameter on reduction rate of fracture strength were more complex. There existed a best range of resin content and fiber bundle diameter. The microscopic observations show that folding resulted in piling up of resin and damage of reinforcing fiber, which would decrease the mechanical properties.

Optical methods for non-contact measurements of membranes

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes. The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements). Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles.

Vibration and Damping in Three-Bar Tensegrity Structure

The most interesting examples of tensegrity structures are underconstrained and display an infinitesimal flex. In the direction of that flex the force-displacement relationship is highly nonlinear, resulting from geometric stiffening and influenced by the effect of prestress at equilibrium. A tensegrity structure would therefore display nonlinear vibrations when excited in the direction of the infinitesimal flex, the “frequency” decreasing with amplitude. Movement in the direction of the flex occurs with only infinitesimal change in member length, and therefore under conventional models of material damping in members the motion would not vanish as rapidly as it would for a conventional oscillator. We study one particular tensegrity geometry for which we present the force-displacement relationship in analytical form and then examine the nonlinear vibrations. We observe the role of damping and we discuss those implications for the design of tensegrity structures in space applications.

Damage Tolerance and Assessment of Foam-Inflated Aerospace Structures

Design and operational issues with respect to the use of inflatable-deployable foam-rigidized components in aerospace structures are investigated in this paper. The sample structures used in this study are fabricated from flexible Kapton film formed into a cylindrical shell by bonding a flat sheet along a longitudinal seam. This tubular shell is injected with a hardening urethane foam to form a composite strut coupon. As with all structures touted for aerospace use, the survivability of foam-rigidized structures when subjected to a micrometeor flux is of interest. This issue is investigated in this paper by performing two controlled experiments: (1) Foam-rigidized test coupons were evaluated in their pristine state to determine structural properties, severely damaged in a controlled fashion, and then evaluated again to compare the undamaged to damaged behavior; and (2) a single specimen was repeatedly tested and then slightly damaged to examine how structural behavior evolves as damage accumulates. The results of these experiments are then used to draw conclusions about the utility of foam-rigidized structures in space applications, including an evaluation of appropriate structural health monitoring strategies.