Experimental measurements of the strain and pressure of rotor blades are important for understanding the aerodynamics
and dynamics of a rotorcraft. This understanding can help in solving on-blade problems as well as in designing and
optimizing the blade profiles for improved aerodynamics and noise attenuation in the next generation rotorcraft. The
overall goal of our research is to develop a miniature wireless optical sensor system for helicopter on-blade pressure and
strain measurements. In this paper, leveraging past and current experiences with fiber optic sensor development, a proof-of-
concept of fiber optic pressure/strain sensor system with wireless data acquisition and transfer capability is
demonstrated. The recently developed high-speed, real-time fiber optic sensor demodulation techniques based on low
coherence interferometry and phase-shifting interferometry is used. This scheme enables a Spatial Division Multiplexing
configuration that consists of multiple Fabry-Perot strain and pressure sensors. Calibration of the strain and pressure
sensors is carried out by using commercially available sensors as references. Spin chamber testing of the sensor system
for simultaneous on-blade pressure and strain field measurements is also performed. It is expected that such a sensor
system will result in enhanced robustness and performance for on-blade pressure and strain field measurements.
A comparison of stack load-line (including blocked force and free displacement) as well as dynamic response of two
single crystal PMN-32%PT stacks is provided in this study. The first stack is a 7mm diameter by 0.5mm thickness 60
layer single crystal stack while the second stack is a 6mm diameter by 0.3mm thickness 100 layer single crystal stack.
Blocked force and free displacement measurements were both performed under DC driving conditions. Free
displacement measurements showed that under 500V driving conditions displacements approaching 87&mgr;m (~2500ppm)
and 48&mgr;m (~1450ppm) were obtained for the 6mm and 7mm diameter stacks, respectively. Experimental blocked force
measurements correlated well with theoretical predictions with experimental values approaching 709N and 685N for the
6mm and 7mm diameter stacks, respectively. The error between the theoretical predictions and experimental values was
attributed to the linear load line assumption in the theoretical model whereas the stack stiffness is dependent upon the
applied force. Dynamic measurements performed under a pre-stress of 4MPa indicated an increase in the strain at
frequencies above 500Hz for driving frequencies up to 1000Hz. This was unexpected as the PMN stack resonance was
calculated to be on the order of several kHz.
An automotive suspension strut is proposed that utilizes compressible magnetorheological (CMR) fluid. A CMR strut consists of a double ended rod in a hydraulic cylinder and a bypass comprising tubing and an MR valve. The diameter on each side of the piston rods are set to be different in order to develop spring force by compromising the MR fluid hydrostatically. The MR bypass valve is adopted to develop controllable damping force. A hydro-mechanical model of the CMR strut is derived, and the spring force due to fluid compressibility and the pressure drop in the MR bypass valve are analytically investigated on the basis of the model. Finally, a CMR strut, filled with silicone oil based MR fluid, is fabricated and tested. The spring force and variable damping force of the CMR strut are clearly observed in the measured data, and compares favorably with the analytical model.
Experimental and analytical validations of a Galerkin analysis of sandwich plates is presented in this paper. The 3-layered sandwich plate specimen consists of isotropic face-plates with surface bonded piezo-electric patch actuators, and a viscoelastic core. The experimental validation is conducted by testing sandwiched plates that are 67.31 cm (26.5') long, 52.07 cm (20.5') wide and nominally 0.16 cm (1/16') thick. The analysis includes the membrane and transverse energies in the face plates, and shear energies in the core. The shear modulus of the dissipative core is assumed to be complex and variant with frequency and temperature. The Golla-Hughes-McTavish (GHM) method is used to account for the frequency dependent properties of the viscoelastic core. Experiments have been conducted on sandwich plates with aluminum face-plates under clamped boundary conditions to validate the model for isotropic face-plates. Symmetric and asymmetric sandwiches have been tested. The maximum error in damped natural frequency predictions obtained via the assumed modes solutions is less than 11%. Analytical studies on the influence of the number of assumed modes in the Galerkin approximation, and the temperature variation, have been conducted. Error in the first plate bending mode is 112% when only a single in-plane mode is used; error reduces to 3.95% as the number of in-plane modes is increased to 25 in each of the in-plane directions. The study on the temperature influence shows that every plate mode has a corresponding temperature, wherein the loss factor is maximized.
We present and review methods of frequency response analysis for cantilevered sandwich beams consisting of aluminum face plates and passively constrained damping layers at the mid- plane. These analysis methods include: (1) progressive wave method, (2) assumed modes method, and (3) finite element method. The progressive wave method accounts for the frequency dependent complex modulus in analyzing the frequency response function. In the assumed mode and FEM analyses, the frequency dependent complex modulus is assumed to be a constant over the frequency range of interest (i.e. the first three modes). By selecting the value of complex modulus to nominally correspond to the second modal frequency, the error in predicted natural frequency can be minimized. However, this comes at the cost of increased error in the damping ratio predictions which are minimized by selecting the value of complex modulus corresponding to the first mode.