Negative-Poisson’s-Ratio (NPR) Microstructural Material by Soft-Joint Mechanism
Y-W Lu, C-J Chang, P-T Lin and H-C Gea
Rutgers University, US
PDMS, microstructural material, compliant mechanism
We present an example of making a negative-coefficient material - Negative Poisson’s Ratio (NPR) material, which expands in the cross section when stretching. The NPR materials can provide unique characteristics in energy absorption. The NPR material developed here is low-cost and can sustain larger strains. The design methodology starts with a design problem and is transformed into a topology optimization problem with volume constraints. The solution is identified as a compliant mechanism with a re-entrant honeycomb structure for the maximum transverse expansion. The gray levels of the elements represent their compliance levels. The darker regions signify higher stiffness while the brighter regions signify higher compliance.
A process utilizing a soft material for the brighter elements and a rigid material for the darker elements is proposed. The rigid element made of resin-elastomer composite by using stereolithography, and the compliant element made of elastomer by using micromolding. The composite has the resin as the ‘bone’, providing the necessary rigidity, while the elastomer serves as the soft joints, bearing the deformation in the structure.
Three different material designs, including soft, rigid and bone-and-soft-joint materials, are fabricated and tested. The results verifies the fabrication of microstructural materials and the consequential design with a better NPR property in a larger strain.
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Nanotech 2006 Conference Program Abstract