Power Armoring the Marines against blasts

Question

The scenario: Near future robotics technology has an energy storage breakthrough, and one of the many implications is battery operated powered suits of armor become a viable technology for soldiers for short duration mission.

These particular armoring devices are built AS suits of armor that are powered, not mecha or vehicles that soldiers ride around in. The reasoning for this is the need for these soldiers to reach where unarmored people can go. This means an imposed size limitation, which further means armor limitation.

With the on-following requirements and descriptions, At what point are explosive blasts a reasonable threat to the occupant? What kind of blasts are survivable with this armor? With/without shrapnel effects?

• Assuming real-world materials for all construction. The only hand-waving is the power source (and perhaps a little with the mechanical construction).
• Assume the thickness and design of the armor is such to offer maximum protection WITHOUT impeding the user’s ability to function, ex use weapons, open doors, flick switches, turn around in a hallway, go up or down stairs.
• Assume a general armor thickness of around ½ inch of rolled homogenous steel equivalent.
• Internal padding should be sufficiently thick to attempt to cushion operators against threats, without causing the armor to become so bulky it cannot be used effectively in tight spaces. The padding should be available within current technology and manufacturing capability.
• The weight of the suit with man inside and in full kit can be assumed to be around 1000 lbs.(A few back of the scratchpad numbers. A cubic foot of steel weighs about 590 lbs. An average human male has a surface area of 1.9 m2 / 20.45 ft2. Spreading that material evenly over that surface gives something like a little more then 1/2 inch of protective material all over. less ~200 lbs for the man, leaves ~100 lbs for a power source and ~100 lbs for equipment.)
• To “survive a blast” Limbs need not remain included; just a reasonable chance of survival if a medic is on hand.

Note, I’m looking for blast/explosion type survivalbility; its easy enough to look up how any given round would do against a ½ inch of steel, Im more interested in the ability of this kind of armor to deal with explosives.

To help direct answers towards what I'm looking for: Can a user survive a grenade thrown at its feet? How far away from a 1-ton open air explosion would they need to be to survive it? How much would armor like with a padded interior actually protect against explosion over-pressure and shock effects? Are the joints weak-points? If so, How much so?

Answer 1

Firsthand Expierience

I fought in Afghanistan and Iraq, I've actually survived 3 different blasts, two in armored vehicles and one on foot. Here is what you need to know about blast trauma:

1: Blast trauma is not a uniform thing. Different explosives have different burn velocities, which is to say that something crudeley made out of anhydrous ammonia and aluminum powder is going to be slower burning and more of a "slow push" in comparison to a faster more energetically burning explosive like C4 or LX14. A pound of LX14 directly against or underneath the suit will throw your power armored armored Marine head over heels about 100 meters and probably liquefy his brain and organs regardless of armor thickness. A pound of anhydrous ammonia and aluminum mix is probably just going to trip him and maybe cause a lot of bruising and light tendon damage to his legs. I've actually seen unarmored personnel stand directly on top of a pound of home made anfo/aluminum explosive and only lose a foot. Distance from blast is also a big deal. Only a short distance from a blast can drastically change what kind of pressures are being exerted. Once 300 pounds of god knows what detonated 40 feet away and we all had concussions but were fine. Another time I saw a Humvee get flipped by only 40 pounds of very low yield home made explosive. Sometimes only a few feet can be the difference between a serious concussion or immediate death.

2: Shaped explosives change everything. As a rule of thumb a shaped charge made from C4 or equivalent will penetrate twice as much armor as it is wide in diameter. So a 4" diameter shaped charge of C4 will penetrate 8 inches of homogeneous rolled steel under ideal conditions. I think video games and movies have made the term spalling pretty universal (when penetrated armor will throw shrapnel on the opposite side). But most folks don't know the effects of over pressure in confined spaces. When a shaped charge penetrates a vehicle the pressure outside the hole is much much higher than that inside. The blast kinda funnels inside the vehicle, then, as the blast pressure dissipates outside it moves back outside again, this is all ocurring at several times the speed of sound. This means temperatures of thousands of degrees with crazy high pressures incinerating anything inside the vehicle before blowing it back out of the hole which is about the diameter of your thumb. It will also sympathetically detonate any fuel or ammo on board in addition to basically cremating the crew and expelling their atomized remains out of the newly made hole. Its actually how we are able to blow up main battle tanks with a missile that only has 8 pounds of LX14 on board, we cheat by making the internal-pressure high enough to detonate the tank's ammo and fuel and destroy itself for us with its own ordinance.

So with this knowledge in mind you armor will not be able to withstand any kind of direct blast except maybe very very small ones from home made inefficient explosives. It will however, give awesome protection from shrapnel and make your chances of surviving a nearby explosion much much higher. Your armor is about the equivalent to being inside a Humvee, which doesn't sound like much until you factor in the fact that its a suit of powered armor and not a large vehicle. There is a downside however, there is basically no way to get swift medical aid to a person who has just survived a blast while they are closed up inside the armor. This means that surviving a blast only to bleed to death from a lost limb or die from trauma before a medic can cut you out of the tin can is a real problem. There could be fast release safety features in place, or even on board automated medical response ability (maybe auto-tourniquets, IV administered blood volumizers, oxygen supply, built in defibrillator etc etc) but these things just took an explosion too! So that means that up to anything that cant breach it or cause a casualty its incredible protection. After anything that can breach it or cause a casualty the same armor that prevented a lethal event from outright killing you can very possibly become a liability the prevents further life saving measures from being successful. MRAP's were god-awful for that. Doors would get all warped and stuck and nobody could get to the people inside who were alive but injured in a swift manner. Power Armor would be even worse for this.

Answer 2

The armor wouldn't be made of steel. You'd look at a composite of ceramics, carbon nanotubes and graphene which would give you a strength far greater than steel at a fraction of the weight.

Now surviving a grenade isn't that hard as it's the shrapnel that kills (usually) but larger blasts it's the shock wave that kills.

Looking a study into G force, a racing car driver will sustain a brain injury around 16% of the time during a crash involving forces of 50G or greater and that's with the helmet and roll cages.

Basically with a big enough blast, it really doesn't matter about how good the armor is, you can scramble the egg without breaking the shell