Modeling and Testing of Fluidic Flexible Matrix Composite Lead–Lag Dampers

A new lead–lag damper concept using a fluidic flexible matrix composite (F2MC) tube is presented in this paper. A model is developed for an articulated rotor blade integrated with an F2MC damper consisting of an F2MC tube, an inertia track, an orifice, and a hydraulic accumulator. Benchtop tests using a 4.5-ft rotor blade demonstrate the performance of a smallscale F2MC damper. The blade–damper system model predictions are verified by comparing experimentally measured and model-predicted frequency response data. In benchtop tests, the model predicts blade damping ratios of up to 0.34 with the F2MC damper. A simplified articulated blade based on the UH-60 rotor is simulated to assess the feasibility of a full-scale F2MC damper. Simulation results predict that the damper can generate blade damping ratios of over 0.30 at low blade lag angles.

Coupled and Multimode Tailboom Vibration Control Using Fluidic Flexible Matrix Composite Tubes

This paper covers the modeling and testing of a helicopter tailboom integrated with a fluidic flexible matrix composite (F2MC) damped vibration absorber. In an advance over previous work, the F2MC absorber presented in this paper treats a combination of tailboom lateral, torsional, and vertical vibrations. A finite element structural model of a laboratory-scale tailboom is combined with a model of attached F2MC tubes and a tuned fluidic circuit. Vibration reductions of over 75% in a coupled 26.8-Hz lateral bending/torsion tailboom mode are predicted by the model and measured experimentally. These results demonstrate that F2MC vibration control is viable at higher frequencies and for more complex vibration modes than previous research had explored. A new absorber with a fluidic circuit that targets two tailboom vibration modes is designed and experimentally tested. On the lab-scale tailboom testbed, the absorber with this circuit is shown to provide vibration reductions of over 60% in both a 12.2-Hz vertical mode and a 26.8-Hz lateral bending/torsion mode. Using this new absorber, vertical and lateral/torsion mode damping are achieved with almost no added weight relative to a purely vertical absorber.

Experimental Demonstration of a Vibration Absorber Using Braid-Sheathed Fluidic Flexible Matrix Composite Tubes

Fluidic flexible matrix composite (F2MC) tubes are a novel type of lightweight, low-profile passive fluidic vibration treatments for structures. Two pairs of F2MC tubes are installed onto a laboratory-scale helicopter tailboom structure and interconnected through a fluidic circuit, resulting in a tuned vibration absorber. The experimental frequency response of the absorber-treated tailboom shows a response amplitude reduction of over 70% for the first vertical bending mode. By partially restricting flow through an orifice in the fluidic circuit, a damped absorber is achieved that adds nearly 8% damping to the first vertical bending mode. The effect of fluid prepressure and tailboom forcing amplitude are also studied. The experimental results show excellent agreement with model predictions.

Dynamic response and validation of a flexible matrix composite

Testing and predicting the dynamic response of flexible matrix composites in impact loading condition face two primary challenges: (i) experimentally, existing techniques using existing instruments do not always provide high fidelity material data under simultaneous high strain and high strain rate loading conditions; and (ii) finite element simulations of a highly flexible material require many material parameters and complex mathematical formulations. To address these limitations, this research investigation presents a technique originally developed in-house for modeling and validating hyper-viscoelastic materials and applies it toward the flexible matrix composite. Results from a simple low-velocity impact (2 m/s) test on a 75 × 75 mm2 flexible matrix composite indicate that the critical material properties for the low strength, highly deformable matrix in conjunction with an updated constitutive model can accurately predict the dynamic behavior within 10% with respect to the force time history response using MATLAB and ABAQUS/Explicit. Finite element interrogation also shows full field stress response within the composite specimen not easily measured via sensors and deformation matching the behavior observed via high-speed camera. Finally, on-going research in this arena indicates that the technique can be applied to higher rate loading mechanisms, such as a gas gun and Hopkinson bar apparatus, in order to obtain material parameters for even more devastating impact loading strain rates.

A Flexible-Matrix-Composite Hydraulic Engine Mount

An effective hydraulic engine mount (HEM) should acquire a high dynamic stiffness (storage and loss) at low frequency, and low dynamic stiffness at high frequency. A passive hydraulic engine mount which can achieve this hard/soft dynamic stiffness requirement is proposed. Three new approaches are adopted in the proposed HEM: elimination of the decoupler, application of a hyperbolic flexible-matrix-composite pumping chamber, and employment of two oppositely connected identical HEM. The working principle of the proposed HEM is explained, the mathematical model is introduced, and the effect of the various physical parameters of the physical model on the dynamic stiffness are presented. It is shown that the proposed HEM can achieve the hard/soft requirement over a specific frequency range.