DESIGN OF INTELLIGENT MATERIAL SYSTEM BY COMBINING THE CONTROL WITH EVALUATION OF SHAPE MEMORY ALLOY

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The shape memory effects of TiNi fiber reinforced metal (Al) or polymer (epoxy) matrix composites were developed for enhancing their mechanical properties as well as for clarifying the strengthening mechanisms, especially, of tensile strength and fatigue resistance. The yield stress and fatigue resistance were observed to increase with prestrain at temperatures above austenitic finish temperature of shape memory TiNi fiber (A_f) as a reinforcement. The increasing mechanism of fracture toughness K value was also discussed experimentally by the changes of photoelastic fringe pattern at a crack-tip of TiNi/epoxy composite model. These sttengthening effects were found to be atrributed to the compressive stress field in the matrix which is induced when the prestrained TiNi fibers shrink to its initial length upon heating above A_f. The predictions based on the analytical model agree reasonably well with the experiments.Next, as an expanded application of this study for active fracture control, a smart composite material system with SMA actuator as well as acoustic emission (AE) sensor was developed in which a typical AE outbreaks was utilized as a trigger to start to control the strengthening the bulk composite by shape memory shrinkages of TiNi fibers under the commands of heating from amicrocomputer linked with AE sensor.