Realistic Captain America Shield

Question

What's the best current material for making something like Captain America's shield?

Important Properties:

• Strong enough to withstand (almost) all physical hits and bullet fire
• Light enough to be thrown like a frisbee (by someone with a lot of strength?)
• Bonus: Is magnetic

I assume there's no material in existence that has the above properties, but is there something that is strong enough to withstand a reasonable amount of force while still able to be thrown by someone with incredible (within human limits) strength?

Answer 1

You're Looking for a Shield-Sized Trauma Plate

When considering the basic requirement - being bullet proof - I think the best thing we can do is find a good Trauma Plate and scale its size up.

Ceramic trauma plates are very good, but are not normally re-used because they tend to crack or develop micro-fissures that could lead towards catastrophic failure after another impact. When re-use is a consideration, Steel or Titanium are the most used metals.

Regarding Weight

This is where I think titanium is going to really run away. This link gives the volume of the shield of between 0.00227 – 0.00454 m3. We also know the density of steel (~8,050 kg/m3) and titanium (~4500 kg/m3).

That would mean a steel shield would weigh between 18.27 and 36.547kg (40.2 - 80.4lbs). A titanium shield would weigh between 10.215 and 20.43kg (22.5 - 40.9lbs).

NOTE however that the shield weight is calculated based on Captain America's shield. It's likely that many types of gunfire could rip through the shield at that thickness using real materials. So let's assume that we are stopping only small munitions fire. Otherwise you need to start multiplying the weight considerably, and even a 2x factor is enough to make the entire endeavor utterly impractical.

Throw Distance

Looking at throwing distance, let's consider the closest analogue we have for throwing really weighty things... the "weight throw" event of track and field. Women use a 20lb ball , which is analogous to the lowest end of the titanium weight scale. The record in that category is 24 meters (around 79 feet). Men use a 35lb ball - lighter than the steel shield but within bounds for titanium - and the world record is 25.8m (~78 feet).

Mind you, in "weight toss" you get a run up and a more ergonomic handle to launch with than you would find in a shield. My estimate is you could probably halve those numbers at best for heavy shield tossing.

Magnetism (as requested)

Steel can be magnetic or not, depending on how it was produced. Titanium is generally nonmagnetic, to the point that a patient with titanium implants can be scanned by an MRI safely.

Answer 2

@GrinningX is on the right track. I'll add detail based on existing bulletproof materials and standards.

The Requirements

What you're looking for is NIJ Level IV protection. Level III will stop a 7.62mm rifle round such as fired from an AK-47. With about 2000J of energy it's the most powerful bullet Cap is likely to encounter on a modern battlefield.

But Captain America's shield was for WWII. Bullets were a lot more powerful back then. He'd be facing things like .30-06 Springfield used by the US in WWII or 7.92 x 57mm Mauser used by the Germans. These are in the 4000J energy range. For that you need Level IV protection.

Then there's the V₀ rating, the most energy a bullet can have and never penetrate. For example, if we say Cap's shield has a V₀ for .30-06 then it means you can fire .30-06 at it all day and none will penetrate. This is a tall order. Each high energy impact will make small bends and cracks in armor and they will add up.

The more realistic measure is the V₅₀ rating, the most energy a bullet can have an only penetrate 50% of the time. 50% doesn't sound like great odds when it's your chest on the line, and nothing about Captain America is 50%.

Most body armor is made up of layers to absorb and distribute the shock of impact, a combination of soft armor like Kevlar and hard armor like steel and titanium, all backed up by your squishy flesh. Cap's shield has none of these advantages. It acts as a "stand alone plate" meaning it will protect with nothing behind it.

The Shield

• A stand alone plate
• Roughly 75 cm in diameter
  • Roughly 4600 cm²
• Providing Level IV protection
• With a V₀ at .30-06
• And throwable by an Olympian

This is a tall order.

The lightest stand alone level IV plates I've looked at weigh about 4 to 5g per cm². That means a 4600 cm² shield will weigh 18 to 23 kg, significantly more than the comic's 5.5 kg. Worse, these are ceramic and only guaranteed to stop ONE level IV shot. Captain America cannot have his shield shatter after one shot.

This isn't going to work.

Lowering Expectations

In order to make this work we're going to have to lower our requirement to level III and ease up on the V₀ requirement. Sorry Cap, you'll have to hope the Germans have submachine guns and StG 44 assault rifles and do some ducking. Or maybe this is a modern Captain America.

You can get a titanium-steel multi-hit hard armor level III stand alone rifle plate. They're about 1cm thick and still 4 to 5g/cm2. This still leaves Cap with a 20kg shield.

The Throw

For comparison, regulation Men's Discus uses a 2kg disc. This shield is ten times that.

Regulation Men's Shot Put is 7kg, still three times less than our shield.

To get into the right scale we need to look at the Highland Games. The heavy weight ball (on a chain) is 4 stone (25.4kg). Finally, we're in the ballpark. The Irish record is 9 meters. An impressive distance in a sporting event, but not a terribly effective ranged weapon.

Unless he hopes the bad guys will laugh themselves stupid as he heaves his only protection 10 yards towards them, I think Cap is better off using the shield as a shield and shooting the bad guys with a pistol.

The Ergonomics

A M240 machine gun weighs about 15kg loaded. It's considered very heavy (the M249 weighs 10kg). If you want to lug one around you generally do it with a sling.

It's still lighter than our shield.

Cap is expected to hold something even heavier with one arm, run and jump with it, move it quickly to block shots, and swing it to clobber enemies.

Make The Shield Smaller

We're not going to get any lighter material. At this point you'll have to cut down on the size of the shield and probably make it square. A more reasonable a 50 cm x 50 cm gives a 12.5 kg shield still wide enough to fully cover Cap's broad shoulders.

This is still very heavy and unwieldy, but puts it in the range of a very heavy automatic weapon.

There's good news for the throw. This puts it closer to the 35 lb (15.9 kg) weight throw, the record for which is 25 meters. Still, that's probably at a high arc and not a graceful Frisbee, unlikely to be terribly useful in combat. It's not going to bounce back, so he's thrown away his protection.

Still probably better off with a pistol.