Stilt WErks
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3 Loading and Measuring Equipment

            Testing and analysis was performed in the Structures and Mechanics Laboratories of Duke University. Test articles were loaded at tip using a Tinius-Olsen model 10000 load frame. This load Frame has a ten-thousand pound force capacity. It is Ball-screw-actuated and applies displacements at the screw-location points by a stiff reaction frame, which, in turn, was bolted to the load frame. The applied displacements and the resulting forces, due to bending and deformation of the test article, were digitized using a 16-bit analog-to-digital converter. The calibration of the sensors was confirmed and the digitized data were scaled to units of inches and pounds

4 Test Results

            All four test articles were bent to a tip deflection of
D = 1.5 inches without causing any noticeable damage.
            All four test articles wxhibited linear elastic deformation up to attest displacement of D = 1.5 inches and a tip force of P = 1600 pounds.

            Force versus displacement plots of the four test articles are shown in Figure 2.

            The test articles were significantly stiffer and stronger than anticipated. We believe that the extraordinary strength and stiffness of the retrofitted test articles is due to excellent bonding between the Urethane and the Aluminum tube, lateral confinement of the Urethane by the Aluminum, and very high Poisson ration (greater than 0.45) for the Urethane.

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