CONTROL OF THE NATURAL FREQUENCIES OF NITINOL-REINFORCED COMPOSITE BEAMS

The natural frequencies of flexible fiberglass composite beams are con trolled by activating optimal sets of shape memory alloy (NITINOL) wir es which are embedded along the neutral axes of these beams. The under lying phenomena influencing the behavior of this class of composite st ructural members are presented. The individual contributions of the fi berglass-resin matrix, the NITINOL wires and the shape memory effect t o the overall performance of the composite beam are determined at diff erent operating temperatures and initial preloads of the wires. The mo des of vibration of the fiberglass beams are measured with and without the NITINOL reinforcement at various operating conditions. With prope rly designed NITINOL reinforcement, it is shown that the beams can bec ome stiffer and less susceptible to buckling. The modes of vibrations of the activated NITINOL-reinforced composite beams can also be shifte d to higher frequency bands relative to those of the unactivated or un -reinforced beams. Finite element model is developed to described the interaction between the NITINOL wires and the fiberglass-resin matrix. Close agreement is obtained between theoretical predictions and exper imental results. With such tunable characteristics, the NITINOL-reinfo rced composite beams can be effective in attenuating the vibrations in duced by various external disturbances. (C) 1995 Academic Press Limite d