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Presentation
Characterization
of Shape Memory Alloy Wires
Used
in Bias Spring Actuators
Afzal
Khan
Doctoral
Student
Mechanical
and Aerospace Engineering
The
George Washington University
Wednesday,
March 29, 2006, 11 am
Phillips
Hall 7th Floor Conference Room # 736
Shape memory alloys
(SMAs) are a group of metallic alloys that return to a previously
defined shape or size in response to thermal change. The stress and
strain developed during transition in SMA wires is commonly used for
mechanical actuation, but the applications of SMAs are widely spread in
the fields of civil, mechanical, biomedical and aerospace engineering.
Devices can be manufactured from commercially available forms of SMA
wires, tubes, thin sheets, ribbons and springs.
The response of shape
memory alloys is dependant upon the thermo-mechanical conditions such
as initial load and temperature. In addition to these state variables
the transformation phenomenon is a function of the ratio and
composition of the alloy's constituents and the heat treatment or cold
working that goes into the material during manufacturing. The behavior
of SMA from different manufacturers and even different batches produced
by the same manufacturer varies significantly. A precision instrument
that characterizes shape memory alloy wires, used in bias spring
actuators, is presented here with experimental determination of the
properties of the alloy. Parameters such as, Young’s modulus,
transition temperatures, and the effect of change in the initial
conditions on the transformation path is presented with the
determination of simulation parameters that are used in SMA
constitutive models.