The proprietary Fly-Bag uses several different high-strength, Aramid-based fabrics, some of which have yarns coated with shear thickening fluid. The inside of the bag is coated with a high-strength elastomer that acts as a gas seal. The floor is constructed of a glass fiber sandwich. “The floor plate had to be stiff enough to accept bags and workers, but lightweight and able to decouple the blast shock,” says Warren.
The researchers tested several sandwich architectures by detonating explosives on a standard fabric pack on the sandwich and comparing the performances. “We required something that spreads the load temporally and spatially,” says Warren. “From the lessons we learned in the tests about fiber concentrations, resin types, resin process, foam infill and relative sandwich thickness, we honed in on what we wanted.”
The team designed two rigs for testing multiple layers of various materials—one small and one large. In small-scale tests, Warren’s team assessed the stiffness and burst strengths of fabrics under high-rate loading and quasi-static pressure loading. They used a small-volume pressure chamber venting into a similar chamber, closed at its free end with fabric. Based on those results, the team selected materials for a large-scale test in a 1 x 1 x 1-meter steel box open on one side. The opening was covered with the composite fabric and explosives were detonated beneath it.
A prototype of the full-size Fly-Bag has been tested using actual luggage. “It worked as planned!” says Warren. The University of Sheffield is now working to produce the Fly-Bag, either by licensing the technology or partnering with a consortium of European companies.