INSTRUMENTATION DESIGN FOR DYNAMIC AXIAL-COMPRESSION OF CYLINDRICAL TISSUE SAMPLES

A rigid pendulum was constructed with a 2.15 kg head so as to load hor izontally mounted cylindrical fruit or vegetable tissue samples at a c onstant strain rate to a preset maximum strain. Crosshead (hammer) spe eds sufficient to cause impulse loaning (typically > 1 m s(-1)) requir ed force measurement at both the anvil and the hammer to account for d ynamic effects. Hammer position was measured with a highly sensitive a ngle displacement transducer (ADT), Sample preparation equipment consi sted of a cork borer rotating in a drill press and a pneumatic saw wit h parallel blades spaced 15 mm apart to trim the samples to a uniform length. Stress-strain results for several materials including potato, apple, starch foam , PVC foam cushioning, and a spring are shown for a range of loading velocities to give examples and demonstrate strain r ate effects. Impulse loading was the dominant dynamic phenomenon obser ved. Force measurement on both ends of the sample allows analysis of t he wave caused by impulse loading and measurement of shock wave speed.