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Research Papers

Modeling, Prototyping, and Testing of Helical Shape Memory Compression Springs With Hollow Cross Section

[+] Author and Article Information
Igor Spinella

Department of Engineering Sciences and Methods, University of Modena and Reggio Emilia, Reggio Emilia 42100, Italyigor.spinella@unimore.it

Eugenio Dragoni

Department of Engineering Sciences and Methods, University of Modena and Reggio Emilia, Reggio Emilia 42100, Italyeugenio.dragoni@unimore.it

Francesco Stortiero

 Technosprings Italia s.r.l., Besnate (VA) 21010, Italyf.stortiero@technosprings.com

J. Mech. Des 132(6), 061008 (May 25, 2010) (9 pages) doi:10.1115/1.4001601 History: Received December 19, 2009; Revised March 20, 2010; Published May 25, 2010; Online May 25, 2010

Shape memory alloys (SMAs) are used in many applications as actuators. The main drawbacks that limit the use of the SMAs in the field of mechanical actuation are the low mechanical bandwidth (up to a few Hertzs) and the unsatisfactory stroke (several millimeters). This paper contributes to enhancing the performances of SMA actuators by proposing a new SMA helical spring with a hollow section. The hollow spring is modeled, then it is constructed, and finally it is tested in compression to compare its performances with those of a spring with a solid cross section of equal stiffness and strength. Emptied of the inefficient material from its center, the hollow spring features a lower mass (37% less) and an extremely lower cooling time (four times less) than its solid counterpart. These results demonstrate that helical springs with a hollow construction can be successfully exploited to build SMA actuators for higher operating frequencies and improved strokes.

FIGURES IN THIS ARTICLE
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Copyright © 2010 by American Society of Mechanical Engineers
Topics: Springs
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References

Figures

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Figure 1

Longitudinal section of (a) hollow and (b) solid helical springs

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Figure 2

Simplified stress-strain curves of a shape memory alloy in martensitic and austenitic states

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Figure 3

Schematic of the experimental setup for the electro-thermomechanical characterization of the springs

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Figure 4

Theoretical dimensionless properties of the hollow spring as a function of the void ratio (data from Ref. 16)

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Figure 5

Free shapes of the (a) hollow and (b) solid springs after manufacturing

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Figure 6

Load-deflection curves of the hollow spring at different temperatures

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Figure 7

Load-deflection curves of the solid spring at different temperatures

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Figure 8

Transients of the force on constrained hollow and solid springs (applied deflection=10 mm) upon electric heating and convective cooling

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