Research Papers

Analysis of a Compressed Bistable Buckled Beam on a Flexible Support

[+] Author and Article Information
J. Beharic, T. M. Lucas

Electrical and Computer Engineering Department,
University of Louisville,
Louisville, KY 40208

C. K. Harnett

Electrical and Computer Engineering Department,
University of Louisville,
248 Shumaker Research Building,
2210 S. Brook Street,
Louisville, KY 40208
e-mail: c0harn01@louisville.edu

1Corresponding author.

Manuscript received November 21, 2013; final manuscript received April 17, 2014; accepted manuscript posted April 22, 2014; published online May 5, 2014. Assoc. Editor: Taher Saif.

J. Appl. Mech 81(8), 081011 (Jun 05, 2014) (5 pages) Paper No: JAM-13-1481; doi: 10.1115/1.4027463 History: Received November 21, 2013; Revised April 17, 2014; Accepted April 22, 2014

The bistable snap-through behavior of a compressed beam is modeled and measured experimentally as its supporting surface is bent through positive and negative curvatures. When the supporting angle of the beam exceeds a critical angle, bistability is lost and only one stable state is supported. The critical angle is controlled only by the initial compressive stress in the beam, and we report a nondimensionalized calculation method for this angle. This large-deflection nonlinear model provides design rules for low-power sensors and actuators that can measure and control surface curvature from the micro- to macroscale.

Copyright © 2014 by ASME
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Fig. 1

Clamped, compressed inclined slender beam and coordinate system for calculations. Half of the symmetric beam is shown. The initial angle θ at (x = 0, y = 0) is α and the final angle θ at x = w is 0. The final y-value, or height of the middle of the beam, is determined by integrating dy/ds from s = 0 to s = L. The two stable solutions are here illustrated for α = 40 deg and β = L/w = 1.15.

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Fig. 2

Relationship between α, substrate curvature radius r, and beam support half-width w. sin(α) = w/r.

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Fig. 3

Stable (zero-applied-force) beam shapes are shown by thick lines. Moving shapes (requiring a vertical force to stay in position) are illustrated by thin lines, for a beam having an arclength-to-gap width ratio L/w of 1.15, and having an inclination angle α of 30 deg.

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Fig. 4

(a) Energy landscape of bistable compressed beam with compression ratio 1.14 for varying center heights and inclination angles. The displacement and inclination axes are nondimensionalized for any thin beam, but the curvature energy on the vertical axis is given in mJ for a three-mil thick, 1 cm wide spring steel beam (E ∼ 200 GPa) spanning a gap width w of 5 cm. (The arclength L for this beam is therefore 1.14 × w = 5.7 cm.) (b) Energy versus displacement trace for this beam with an intermediate inclination angle (30 deg). (c) The vertical force Fv versus displacement for this beam is the negative gradient of plot (b) (“downward force” means to push the center of the beam toward more negative y-values).

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Fig. 5

(a) Setup for experiments with beams having a support width (2w) of 5 cm and symmetric end angles α. (b) Experimental results and prediction for thin plastic and metal strips. Snap-through angle is a function of the compression ratio β, and does not depend on absolute scale or material properties as long as assumptions are met.




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