Air Force Considers Applications of Jamming Model

  • Published
  • By Maria Callier
  • AFOSR
ARLINGTON, Va. --  Granular solids (e.g., salt or sand) and viscous liquids (e.g., toothpaste or wood glue) can behave like solids or liquids, depending on conditions. When these fragile-state materials stop flowing, scientists refer to the transition from fluidity as "jamming." With funding from AFRL, Dr. Pirouz Kavehpour and his team of researchers at the University of California at Los Angeles (UCLA), Henry Samueli School of Engineering and Applied Science, are investigating this phenomenon. As part of their effort, they formulated a thermodynamic model for predicting jamming behaviors in fragile materials. They also developed a Tribo-rheometer system to test the predictive capacity of their theoretical model.

Air Force (AF) officials are interested in what beneficial effects the team's model could bring to the development of new materials enhancing Department of Defense systems. Such prospective materials could range from a new family of lubricants for extreme-environment applications to a new generation of impact-resistant shields.

Fragile materials share common jamming behaviors, but until now, researchers have been unable to establish a common mechanism among the different material types. In devising a thermodynamic approach, the UCLA researchers have discovered a means of predicting the jamming behavior of numerous materials using a single model.

The team began by using an existing model to focus on the behavior of dry sand, introducing a nonthermal temperature in order to measure the fluffiness of the granular material. The temperature variable also made sense for the team's subsequent study of viscous liquids, which become resistant to flow when cooled.

The researchers plan to use their model for various applications in commercial and defense industries alike. Currently, the team is working with AFRL to examine the characteristics of a new family of strong, durable materials with potential applications of interest to the AF.