Twisting Smartly in the
M. Garfinkle; Aerospace
America; July 1994, p18
A Continuous-Fiber Composite Wing Box-Beam Exhibiting Twist-Bend Coupling E.S. Greenhalgh, C.M. Pastore, M. Garfinkle; Composite Engineering; 3 (1993) 691
ABSTRACT - Aerospace organizations devote much effort to developing "smart" structures, load-bearing wing spars whose elastic response to loading can be adapted to varying conditions. Described herein is a continuous wound twist-bend coupled wing spar that does away with manual patch-layup to achieve the desired response.
Smarter Rotor-Blade Composite 'Smart' Spar M. Garfinkle; Materials and Design; 15 (1994) 27
ABSTRACT - Wing box-beams exhibiting beneficial twist-bend coupling can be fabricated by continuous-fiber manufacture using an appropriate application of conventional winding or textile placement techniques. By utilizing a novel "quasi-unbalanced" symmetric stacking sequence the box-beam is balanced, but in terms of bending response it behaves in an unbalanced manner. The twist-bend reponse of box-beams manufactured with this technique has been measured.
Aerospace Airfoil Smart Spar E.S. Greenhalgh, C.M. Pastore, M. Garfinkle; Composite Manufacturing; 4 (1994) 195
ABSTRACT - One of the most exiting developments in fibre-resin composites for aerospace applications are smart structures. In the active embodiment of such structures computer-controlled piezoelectric microactuators are embedded between fibre plies. Suitably controlled by a central processing unit fed data such a pressure, air speed and structural strain, these microprocessors alter the shape of the structure under specific flight conditions. For example, twist-bend coupling could artificially induced in a rotor blade in a rotor-blade spar to minimize vibration or ameliorate excessive blade loading. However, such microactuators are incapable of imposing the loads required for the desired structural deformation and, moreover, behave as sharp discontinuities which can cause local delamination and possible structural failure. In response to these deficiencies a passive structure was developed which intrinsically exhibits the required twist-bend coupling as a result of the fibre architecture selected in the fabrication of the spar. Because the fibre architecture permits the use of continuous fibres, the spar would be highly practical for D-spars that could be incorporated into essentially conventional rotor-blade construction.
ABSTRACT - Aircraft wings and rotor blades are subject to undesirable bending and twisting excursions that arise from unsteady aerodynamic forces during high speed flight, abrupt manoeuvres or hard landings. These bending excursions can range in amplitude from wing-tip flutter to failure. A continuous-filament construction 'smart' laminated composite box-beam spar is described which corrects itself when subject to undesirable bending excursions of flutter. The load-bearing spar is is constructed so hat any tendency for the wing or rotor blade to bend from its normal position is met by an opposite twisting of the spar to restore the wing to its normal position. Experimental and theoretical characterization of thee spars were made to evaluate the torsion-flexure coupling associated with symmetric layup. Predictions of the twist and bend versus load were made for different fibre orientations in laminated spars using a spline function structural analysis. The analytical results were compared with experimental results for validation. Excellent correlation between experimental and analytical value wee found.
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