Team 7

Reusable and Instantly Stiffening Orthopedic Cast

Objective

The primary objective of this project is to create a cast using self-hardening, form-fitting technology by combining granular jamming and layer jamming. The final product must work as well as conventional casts when tested according to ASTM F1536-95 standards--a specialized compression test. Success with the stiffening mechanisms may reshape other protective industries such as body armor and sports equipment.

Small Grain+Layer Prototype: Top Small Grain+Layer Prototype: Bottom Small Grain+Layer Prototype: Wrapped

Background

The strengthening mechanism of this cast is from both granular jamming and layer jamming. Granular jamming is the process of evacuating air from a porous pouch of small grains, such as coffee or flour. As the air leaves the pouch, the grains are pulled tightly together, restricting grain movement and increasing resistance to bending. Layer jamming is the similar process of evacuating air from a pouch, but instead, layers of paper are pressed together tightly. An increase in friction between the papers proportionally increases resistance to bending as well.

Grain Jamming Gripper Example (Credit: Olympus Controls) Layer Jamming Example

Bending creates both compression above the neutral axis and tension below the neutral axis as seen in the figure below. For a beam of grains, the mass in tension is free to move and does not contribute to strength. Because granular jamming strength depends on restricting grain movement , layer jamming was introduced below the neutral axis to compensate for granular jamming's weakness. The neutral axis is defined as an axis where no compression or extension occurs during bending. Ensuring that the coffee grains is below the neutral axis is critical to the success of a combined layer and grain jammer.

Layer jamming also adds the option for composite sensing layers, such as accelerometers and strain gauges. Neither granular jamming nor layer jamming alone provides penetration resistance like a fiberglass and polyurethane cast can, so CB3M hopes to incorporate armor, similar to that of an alligator or gar, to aid in impact resistance. Shear thickening fluids may also be researched for impact resistance.

The final design for our cast is featured below, and can withstand a force of 97.5 N at 10 mm. of compression. The enclosure is made of two rectangular laminate strips that are heat sealed together. A plastic nozzle is fitted and ensured to be airtight with RTV silicone. Neutral Axis Diagram

Final Design