DAMPING ENHANCEMENT IN HYBRID COMPOSITE BY EMBEDDING NICKEL-TITANIUM WIRES SUBJECTED TO MICROSTRUCTURE TREATMENTS
Open Access
- Author:
- Nagrale, Shashank
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 10, 2019
- Committee Members:
- Reginald Hamilton, Thesis Advisor/Co-Advisor
Charles Bakis, Committee Member - Keywords:
- H-doping
Aging
Damping
Carbon fiber composite
NiTi
Shape memory alloy
DMA
DSC
Tensile test
Saravanos-Chamis model - Abstract:
- Carbon fiber reinforced polymer (CFRP) composites are increasingly being used in structures where minimal weight coupled with high stiffness is required, such as helicopter rotor blades. New high-performance helicopters require composite blades with increased damping to avoid dangerously large-amplitude vibrations. Shape memory alloy (SMA) composites have been fabricated with commercially available nickel-titanium (NiTi) SMAs, typically wires, embedded in the interlayers of CFRP laminates in order to augment damping in the composite structure. Marked damping has been reported due to dissipation associated with deformation in the martensitic phase. Measured loss factors of NiTi SMAs have reached as high as 0.013. However, such an increase in damping is insufficient for the helicopter blade application. In this work, commercially available NiTi SMA wires are subjected to aging and hydrogen (H) doping to improve damping capacity of the wires and CFRP composites made with them. A micromechanical model for damping by Saravanos and Chamis is used to predict the damping of SMA composite with different SMA wire volume fractions and two CFRP laminate configurations, [90]6 and [0/±45]s. The current research is the first to explore the low frequency damping improvement in CFRP composites by embedding aged and H-doped NiTi wires. Increased loss factor has been reported for NiTi SMAs after doping with hydrogen. Postulations have been put forth to rationalize that the loss factor was enhanced by interactions of the underlying martensitic deformation mechanism with the H-doped microstructure. NiTi wires were doped with hydrogen, for this work, using gas-solid surface reaction. For hydrogen doping microstructure treatments, temperature and pressure were varied to vary the amount of hydrogen diffused into the NiTi wire. The amount of H diffused into NiTi was predicted using Schmidt’s relation based on Sievert’s law. The H content ranged from 0.001 to 0.0577 H atomic ratio, with hydrogen being found to facilitate embrittlement of NiTi wires. The loss factor in the SMA wire was increased by 500%, due to H doping treatments. For helicopter rotor blades, 1 – 10 Hz loading frequency regime is of interest; relative to the much higher kHz range typically reported. In the low frequency range, this work demonstrates the potential for post processing including H doping as a novel material treatment for significantly enhancing the damping in NiTi based SMA composites. The Saravanos and Chamis model predicts the loss factor of SMA composite to increase as much as 363% for the [90]6 laminate and 185% for the [0/±45]s laminate with the SMA volume fraction of 0.1. With the appropriate heat treatment and shape setting of the wire, the SMA composite with [0/±45]s laminate corresponded to the prediction.