Tunis’ background in composites manufacturing also influenced the project objective to lighten and strengthen the Humvee. “From day one of working in a composites manufacturing company, you set off to make things lighter. In an effort to increase survivability, that key concept became less of a priority as add-on armor increased the overall weight of vehicles in combat,” says Tunis. “Vehicles have to get lighter and this is where high-tech composites like Dyneema can work to provide both high performance and light weight, which pays off in transport and in logistics costs such as fuel.”

Composite Humvee chimney structure connects floor to roof, venting ballistic energy and dispersing the force around the vehicle.

Composite Humvee chimney structure connects floor to roof, venting ballistic energy and dispersing the force around the vehicle.

Integrating composites into the Humvee

The team chose Dyneema, the ultra-high weight polyethylene fiber known for dispersing the speed of sound faster than any fiber in the world, as part of the blast mitigation system to help spread the energy in a blast event. Dyneema is used in other Hardwire armor applications and is also used extensively in manufacturing kite sail lines. As an avid kite boarder, this is how Tunis discovered the material.

Hardwire’s Humvee cab design is an integrated suite of proprietary blast mitigation technologies that includes the structural blast chimney (SBC), a unique hull design, an energy-absorbing floor system, and blast-resistant seats. Composites play a key role in the survivability of the Humvee by incorporating light weight, high performance protection in the cab design. According to John Hammond, vice president of business development at Hardwire, “The key to developing protection for the Humvee was to strike the proper balance between performance, weight, and cost.”

The structural blast chimney is only as wide as a laptop computer and extends from the floor structure to the roof of the Humvee, where the vent is placed to release the extra energy. The flooring system, isolated from the hull structure, uses composites in combination with energy absorbing materials to protect soldier’s feet, legs and lower torso from the blast energy. The proprietary hull design is structurally designed to disperse the incoming blast energy to keep the structure from collapsing on impact. The BLASTtech blast-resistant seats, manufactured by Jankel Tactical Systems in Duncan, S.C., have been used in all of the blast tests to date. They are currently being used in British military vehicle designs and provide extra blast mitigation inside the vehicle.

The entire system is designed to be modular, meaning that it can be upgraded if necessary or removed when not required for the mission. It acts in conjunction with the hull design beneath the floor of the Humvee, increasing its structural capacity to withstand blast energy. Overall, this new Humvee demonstrates occupant survivability to the M-ATV underbody threshold threat level.