Mechanical design of negative stiffness honeycomb materials
- 5.9k Downloads
A mechanical system exhibits negative stiffness when it requires a decrease in applied force to generate an increase in displacement. Negative stiffness behavior has been of interest for use in vibro-acoustic damping materials, vibration isolation mechanisms, and mechanical switches. This non-intuitive mechanical response can be elicited by transversely loading a curved beam structure of appropriate geometry, which can be designed to exhibit either one or two stable positions. The current work investigates honeycomb structures whose unit cells are created from curved beam structures that are designed to provide negative stiffness behavior and a single stable position. These characteristics allow the honeycomb to absorb large amounts of mechanical energy at a stable plateau stress, much like traditional honeycombs. Unlike traditional honeycombs, however, the mechanism underlying energy-absorbing behavior is elastic buckling rather than plastic deformation, which allows the negative stiffness honeycombs to recover from large deformations. Accordingly, they are compelling candidates for applications that require dissipation of multiple impacts. A detailed exploration of the unit cell design shows that negative stiffness honeycombs can be designed to dissipate mechanical energy in quantities that are comparable to traditional honeycomb structures at low relative densities. Furthermore, their unique cell geometry allows the designer to perform trade-offs between density, stress thresholds, and energy absorption capabilities. This paper describes these trade-offs and the underlying analysis.
KeywordsHoneycombs Negative stiffness Bistability Energy absorption Elastic stiffness Stress threshold
Normalized displacement threshold
Out-of-plane depth for a negative stiffness beam
Specific initial stiffness
Modulus of elasticity
Apex height for a negative stiffness beam
Area moment of inertia
Length of a negative stiffness beam
Ratio of apex height to thickness for a negative stiffness beam
In-plane thickness for a negative stiffness beam
Beam-shape coordinate along the vertical axis
Beam-shape coordinate along the horizontal axis
Critical stress level
We gratefully acknowledge Professor Desiderio Kovar and Mr. Sergio Cortes for their help in generating the experimental data in Fig. 5. Tim Klatt was instrumental in generating the negative stiffness honeycomb configuration illustrated in Fig. 2 and conducting preliminary proof-of-concept studies to refine the design. We gratefully acknowledge the funding from the Department of Defense Small Business Innovation Research (SBIR) Program under SBIR Topic N142-085 in collaboration with the Maritime Applied Physics Corporation (MAPC).
- 1.Gibson L, Ashby M (1999) Cellular solids: structure and properties. Cambridge University Press, Cambridge, UKGoogle Scholar
- 4.Correa D, Klatt T, Cortes S, Haberman M, Kovar D, Seepersad C (2014) Negative stiffness honeycombs for recoverable shock isolation. In: Proceedings of the solid freeform fabrication symposium. The University of Texas at Austin, Austin, TXGoogle Scholar
- 6.Klatt T, Haberman M, Seepersad C (2013) Selective laser sintering of negative stiffness mesostructures for recoverable, nearly-ideal shock isolation. In: Proceedings of the solid freeform fabrication symposium. The University of Texas at Austin, Austin, TXGoogle Scholar
- 11.Matbase. Available: www.matbase.com. Accessed 17 Dec 2014
- 12.Leigh D (2012) A comparison of polyamide 11 mechanical properties between laser sintering and traditional molding. In: Proceedings of the solid freeform fabrication symposium. The University of Texas at Austin, Austin, TXGoogle Scholar
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.