Browsing by Author "Schultz, Marc Robert"

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    Energy Absorption Capacity of Graphite-Epoxy Composite Tubes
    Schultz, Marc Robert (Virginia Tech, 1998-11-11)
    The energy absorption capacity of a series of axially crushed composite tubes fabricated from high tow count graphite fiber is compared with those of similar tubes fabricated from aerospace-grade fiber to determine the viability of considering the use of such fibers in automotive applications. To that end, graphite-epoxy tubular specimens with circular and square cross-sectional geometries; stacking sequences with ±45° fibers and with both ±45° and 0° fibers; and two different fiber types were fabricated and crushed both statically and dynamically to examine the energy absorption characteristics. The fiber types, in the form of preimpregnated tow (towpreg) from Thiokol, were Akzo Fortafil 50k fiber and aerospace-grade T300 12k fiber. Using the towpreg, sixteen tubes were filament wound on aluminum mandrels. Three specimens were cut from each of these tubes for a total of forty-eight specimens. Twenty-four of these specimens were crushed statically in a load frame and twenty-four were crushed dynamically in a drop fixture. In order to characterize the tubes and specimens, a number of measurements were taken. These measurements included length, wall thickness, cross-sectional dimensions, volume, and mass. Two important energy absorption measures were examined: the specific energy absorption (SEA) and the ratio of the peak load to the average load. The geometry had a significant effect on the energy absorption but the stacking sequence did not. It was also found that the 50k material was less effective at absorbing energy than the 12k material, but the 50k still may be acceptable.
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    Use of Piezoelectric Actuators to Effect Snap-Through Behavior of Unsymmetric Composite Laminates
    Schultz, Marc Robert (Virginia Tech, 2003-04-17)
    As a new concept for morphing structures, the use of piezoelectric actuators to effect snap-through behavior of simple unsymmetric cross-ply composite laminates is examined. Many unsymmetric laminates have more than one stable room-temperature shape and can be snapped through from one stable shape to another. In this new concept for morphing structures, one or more piezoelectric actuators are bonded to unsymmetric laminates, and are then used to snap the laminate from one shape to another. The actuator would be used to change shape, but would not be required to maintain the shape. Using the Rayleigh-Ritz technique, several models are developed to predict the interaction between the base laminate and the actuator. In particular, the voltage (applied to the actuator) needed to snap the laminate is predicted. The NASA-LaRC Macro-Fiber Composite&174; (MFC&174;) actuator is chosen as the actuator of choice for this work. A laminate is manufactured, an actuator is bonded to the laminate, and experiments are performed. Since the agreement between the initial models and experimental results was not good, the models were revised. Good agreement between the predictions of the revised model and experiment is reached. Suggestions for future research directions are presented.