How MOBIUS Blast-Protected Seats Measure Up to The Dynamic Response Index

The rise of improvised explosive devices (IEDs) has changed the face of modern warzones. Used by insurgents as part of an asymmetric warfare campaign, these homemade bombs have caused approximately 50% of all injuries and fatalities  suffered by American troops in Iraq and Afghanistan. In the process, they have changed the way military forces get from point A to point B: making heavily armored vehicles a necessity for safeguarding the troops willing to put their lives on the line.

In an age of IEDs, the requirements for vehicles has changed considerably. The armored vehicles of yesterday are giving way to new generations of vehicles with significantly more protection than their predecessors. These protective measures aren’t just for the outside of vehicles. Our very own blast-protected seats, the leading seats in their category, have a key role to play when it comes to  mitigating the shock wave occupants encounter during blast events that occur during IED based attacks.

But don’t just take our word for it. Seats for military vehicles are professionally tested in terms of the probability that they avoid injuries to the spine of an occupant during such an incident. Dynamic Response Index (DRI) is the standardized model mandated by the North Atlantic Treaty Organization (NATO) to assess vehicles and innovations such as energy-dissipating seats when facing underbody blast attack conditions. The DRI is a measure of the likelihood that spinal damage will occur in such an incident as a result of a shockwave.

The DRI model was originally developed to study the correlation of spinal injuries to accelerations during helicopter crashes and seat ejections in fixed wing aircraft. However, since then its use has expanded to several other scenarios in which there is the possibility of damage to the spinal column during short duration accelerations. Parameters have been validated through ejection seat studies, catapult tests, and drop tests.

The Dynamic Response Index Equation

The Dynamic Response Index is worked out in an equation that views the spine as a lumped single-degree-of-freedom spring-shock absorber system. This model utilizes a linear second-order differential equation, in which spinal compression is the variable:

d2X/dt2 + 2·ζ·ω·dX/dt + ω2·X = d2z/dt2

In the above equation, X represents spinal compression, d2z/dt2 is time-dependent shock acceleration, coefficients ζ and ω are the lumped spinal damping and frequency, ζ = 0.224 and ω = 52.90 radians/second. The Dynamic Response Index is the maximum spinal compression (Xmax) derived from the differential equation of DRI = (ω2/G)·Xmax, in which G represents the acceleration of gravity (9.806 m/s2).

MOBIUS’ patented SPIRAL technology provides our seats a small but powerful and efficient energy-absorption element which can help mitigate extremely high energy levels. Incorporating our unique SPIRAL tech, our highly ergonomic seats isolate crew members from the vehicle’s body. In the event of an underbelly explosion that might result from an armored personnel carrier or other vehicle driving over an IED or landmine, the seating system is able to absorb and attenuate the force of the blast. Our seats have achieved repeated outstandingly low Dynamic Response Index measures when tested. This is the case even when it is tested under drastic deformations and multi-hit assaults.

Such energy absorbing abilities cannot be overstated in terms of their importance. Even if the armor of a military vehicle is not compromised in an attack, that alone is not sufficient to protect the crews of combat vehicles from potentially devastating shockwaves emanating from IEDs. These shockwaves are transferred through the rigid body of combat vehicles, directly into the troops inside. The results can be devastating.

Delivering on DRI

MOBIUS’ versatile solutions can be implemented in a wide variety of platforms. Not only have they proven to be outstandingly effective, with incredibly low DRI measures, but our seating solution is extremely versatile. SPIRAL technology lets us optimize our design to different seat parameters including (but not limited to) occupant weight, dynamic mass, threat level, and physical characteristics of the vehicle. MOBIUS seats can be retrofitted into a range of vehicles, making full use of available space, and offering maximum protection to everyone from the lightest 5th percentile female through to heavy 95th percentile males.

MOBIUS’ track record speaks for itself. Since 2009, our military vehicle seats have been the preferred solution by leading platform manufacturers in the United States, Israel, and Europe. During that period, upwards of 13,000 units of our seats have been deployed, on more than 45 vehicle platforms, in 25 countries. We don’t want to speculate on how many injuries have been averted and lives saved thanks, in part, to our technology. But when it comes to protecting those who would themselves protect us, we believe that any contribution is worth it.

Want to find out more? If we can be of any assistance, please get in touch with us. Whatever the test that’s thrown at us, we’re confident that our seating solutions can deliver the answer you’re hoping for. Both in the testing lab and on the field.

Photo by Think Defence on Foter.com / CC BY-NC