Shape memory alloy actuation for active tuning of composite beams

This paper presents an experimental - analytical study on the active tuning of composite beams using shape memory alloy (SMA) wires. Two graphite - epoxy composite beams with embedded fused silica tubes (also called sleeves) with `dummy' steel wires inserted in the sleeves were manufactured using an autoclave molding technique. After curing, the `dummy' wires were replaced by pre-strained SMA wires. During testing of such a beam, the beam and SMA wire are independently clamped at both ends and the SMA wires are activated using electrical resistive heating. A large tensile recovery force develops in the wires due to a phase transformation and the mechanical constraints provided by the clamps. The influence of this recovery force on the vibration behavior of the composite beams was determined by vibration testing. Analytically, these beams with SMA wires inserted in embedded sleeves were examined as beams on an elastic foundation; the spring constant of the elastic foundation depended on the axial recovery force of the SMA wire. Good correlation between analysis and experiment was achieved. A numerical parametric study of natural frequencies of composite beams with activated SMA wires was conducted. The parameters considered were the diameter and the number of SMA wires. The numerical study suggests that inserting 25 SMA wires of 20 mils diameter into a graphite - epoxy beam of 30 in length, 1 in width and 62 mils thickness increases its first frequency by 276%.