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Research Papers

Stress Relief in Contact-Aided Compliant Cellular Mechanisms

[+] Author and Article Information
Vipul Mehta

Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802vvm104@psu.edu

Mary Frecker

Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802mxf36@psu.edu

George A. Lesieutre

Department of Aerospace Engineering, Pennsylvania State University, University Park, PA 16802g-lesieutre@psu.edu

J. Mech. Des 131(9), 091009 (Aug 18, 2009) (11 pages) doi:10.1115/1.3165778 History: Received December 04, 2008; Revised April 23, 2009; Published August 18, 2009

Compliant cellular structures with an internal contact mechanism are described in this paper. Contact during deformation reduces failure-causing bending stresses through stress relief, thereby enabling such cellular structures to be stretched more than the corresponding structures without contact. Finite element analysis (FEA) is carried out to simulate the structure. An analytical model is developed to get results quicker than FEA and to develop insight into the mechanics of the deformation process. The error in prediction of the maximum stretching capacity using the analytical model is less than 7% when compared with finite element simulations. Several materials are investigated for such structures. Although the allowable strain of all these materials is small, the overall strain of the contact-aided cellular structures is at least an order of magnitude greater than that of the constitutive material. The contact mechanism and the induced stress relief increase the stretching capacity of the contact-aided cellular structures by as much as 100%. Experiments are conducted to validate the models, and good agreement is found. A high-strain morphing aircraft skin is examined as an application of these mechanisms. The results indicate that the proposed skin structure not only increases the morphing capacity but also decreases the structural mass by 13% as compared with a cellular skin without contact.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Free body diagrams of the cell walls

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Figure 6

Variation in global strain per unit material strain with cell angle for Delrin (solid line—contact-aided structure, dashlike—noncontact structure)

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Figure 7

Variation in global strain per unit material strain with cell angle for zirconia (solid line—contact-aided structure, dashed like—noncontact structure)

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Figure 8

Experimental setup and the aluminum models, without (left) and with (right) the contact mechanism

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Figure 9

Variation in residual strain with global strain. The kink in the contact-aided plot occurs when contact takes place.

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Figure 10

Variation in nondimensional reaction load versus nondimensional extension.

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Figure 11

A variable-span morphing wing (23), side view (top) and cross-sectional view (bottom)

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Figure 12

Comparison of maximum global strain for contact-aided cellular skin and noncontact cellular skin with respect to the cell density

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Figure 13

Comparison of structural mass for noncontact and contact-aided cellular skin with respect to the cell density

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Figure 14

Equivalent skin stiffness in span direction

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Figure 1

Geometry and nomenclature of a contact-aided compliant unit cell

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Figure 2

Cellular structure and boundary conditions applied for FE simulation

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Figure 3

Stress history for noncontact and contact-aided cellular structure

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Figure 4

Delrin prototype of the contact-aided compliant structure: left photo shows initial configuration and right photo shows deformed configuration and contact

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