Tuesday  |  Milwaukee  |  09:00 AM–09:20 AM

#19147, Fabrication and Characterization of Thermoformed Auxetic Foams

Tailoring the Poisson’s ratio of solids has been shown to affect their mechanical and energy absorption characteristics. Auxetic (negative Poisson’s ratio) foams have emerged as cellular solids with unique mechanical and energy absorption properties required for protective gear. This research aims to identify the critical compression ratio, temperature, and thermal treatment time for thermoformed auxetic foams fabricated from non-auxetic polyurea (PU) foams. The choice of polyurea foam is justified by its excellent mechanical and energy-absorbing properties. A three-step thermoforming procedure has been designed and utilized to process auxetic polyurea foams. First, quasistatic compression tests are performed with 2D digital image correlation (DIC) analyses to identify the Poisson’s ratio-strain correlations in as-received non-auxetic foams. The global strains corresponding to the minimum Poisson’s ratios are identified. Foam samples are then compressed in a custom-made aluminum fixture that allows the application of constant axial compressions with lateral confinements. The compressed foam samples are held at different elevated temperatures and for various durations to facilitate thermoforming. Thermoformed foam samples are then removed from the fixture and characterized in terms of stress-strain and Poisson’s ratios. Additionally, the energy absorption efficiency of the foams before and after thermal treatment is characterized and compared. Results obtained in this study suggest that thermoforming can be used as a simple and effective process to adjust the Poisson’s ratio and load-bearing characteristics of foams, leading to improved impact mitigation characteristics.

Bably Das   Rowan University
Brett Boyle   Rowan University
Matthew Leoncini   Rowan University
Nicholas Pagliocca   Rowan University
George Youssef   San Diego State University
Behrad Koohbor   Rowan University