TORSIONAL STIFFNESS OF NITINOL-REINFORCED COMPOSITE DRIVE SHAFTS

The torsional stiffness of composite drive shafts is actively controlled by activating optimal sets of shape-memory alloy (NITINOL) wires which are embedded near the outer surfaces of these shafts and parallel to their longitudinal axes. With such active control capabilities, drive shafts can be manufactured from light-weight sections and their stiffness can be actively tuned to avoid undesirable resonant responses. These features may find applications in drive shafts of critical vehicles, such as helicopters, where high torque-to-weight ratios are of utmost importance. However, more development work must proceed these applications. A finite element model is developed to describe the individual contributions of the composite matrix, the NITINOL wires and the shape-memory effect to the overall performance of the drive shafts. The theoretical predictions of the models are validated experimentally on a prototype of a NITINOL-reinforced drive shaft which is 2.9 cm in diameter and 26.6 cm long. The shaft is reinforced with two NITINOL-55 wires which are 0.54 mm in diameter. The effect of the initial pre-load of the NITINOL wires and of their activation strategy on the performance of the shaft is determined. The experimental results obtained indicate that activating the NITINOL wires results in doubling the torsional stiffness of the shaft. The theoretical and experimental techniques presented will provide useful guides for designing SMART drive shafts.