What kind of natural armor would stop bullets?

Question

It should not resist 50 cal bullets, but an armor which could protect a creature from the US standard issue rifle, for example. Here are a couple of things the armor needs to do:

1. Protect the creature from the bullets mentioned above. Take a look at @computercarguy's answer for more information on the bullets I am talking about.
2. The armor could be created from a chemical in the air into a solid piece of armor, i.e. the atmosphere contains some needed component for the armor. This chemical does not need to be in the Earthen atmosphere, it just needs to be some sort of gas, I'll work out the details of how it got into the creature's atmosphere. Note this is more of set dressing than anything else.
3. The armor should not be much heavier per cubic inch than steel. The creatures could take more, but they still need to be able to lift quite a bit around.
4. The armor could theoretically be "fixed" within a month at the max, but a little longer would be fine. Not a hard requirement.

UPDATE: I am looking for two specific things the other answer is not looking for, repair time and a request for it to be based on things in the environment, a theoretical element which helps build the armor.

Answer 1

Mantis Shrimp Claws will do quite nicely.

Carbon is extremely abundant on Earth's surface and presumably any other Earth-like planet that the author may be working on. Given the many forms that carbon can take from the ultra-soft graphite to the ultra-hard diamond, it should be able to satisfy your needs.

Characteristics of good armor

The element(s) that form this armor are important but the construction/organization of the elements are far more important. If the armor is too rigid, it will shatter. If it's not hard enough, then the bullet will pass through. (An example of a behavior we don't want is spider silk. True, it's stronger than steel at that scale but it's also super stretchy. Stopping a bullet on the other side of the target isn't very useful.) The goal will be to spread the bullet's kinetic energy over a large enough period that the armor plate can handle it.

Mantis shrimp have ridiculously resilient armor. They have to since they hit harder than most anything else in the animal kingdom. Note the many layers of fibers at slight angles to each other. In this configuration, penetrations that break through between two parallel fibers (this is the weakest configuration) runs into the next layer below that is oriented more towards the longitudinal orientation (which is far far stronger). At every layer, the bullet is forced to expend lots of energy breaking the bonds of the fibers along their strongest axis.

Fast Replacement Armor

Requirement 4 is the most interesting. Growing plates like a turtle shell would certainly be effective from an armor perspective however, these don't grow quickly. Human skin doesn't offer any kind of armor capabilities but it does grow very quickly. Skin wounds can heal in a month or less (depending on various factors). Clearly we need something that will grow fast and ideally is always growing. If the armor is damaged, we don't want to have to keep carrying it around for longer than we have to. Lots of animals have disposable "armor" to one degree or another. Humans have their skin. Porcupines have their quills (which are replaced). Snakes, lizards, crabs and lobsters have their skins.

Let's assume this creature is a carnivore so that it can afford the higher metabolic costs of replacing all it's armor in a month or so. Perhaps as a way to reduce this metabolic load, the creature swallows the old armor scales which are then broken down into basic components for the armor-building cells to use.

Alternatively, the outer layers can just flake off after exposure to oxygen for some period. This gives the armor a natural decay rate and prevents the armor from getting too thick. Natural variation in the armor breakdown proteins could lead to some creatures with thicker or thinner armor than others. Hey cool! We just invented a way to get heavy and light versions of the same creature suited for different battlefield duties without having to breed different versions. Win!

Yeah, but how good is it?

Mantis shrimp 'fists' are known to withstand 4 gigapascals. This is about 40k bar or 1/90th the pressures in Earth's core. Dang.

I'm going to assume a NATO 5.56x45mm round. It's super common and well understood. With a muzzle velocity of 990m/s. Kinetic Energy is:

$$KE=\frac{1}{2}mv^2$$ $$\Delta E=F\parallel d$$ therefore $$F=\frac{\Delta E}{d}$$ Assume $E_0=0\text{ J}$

therefore $F=\frac{mv^2}{2d}$. $$P=\frac{F}{A}$$ $$A=\pi r^2$$ therefore $P=\frac{mv^2}{2d\pi r^2}$,

where $P$ is the pressure in Pascals, $m$ is the mass of the bullet in kilograms, $v$ is the muzzle velocity in meters per second, $d$ is the distance the bullet travels in meters, and $r$ is the radius of the bullet. With all that, we get that the pressure exerted on the armor is

$$\frac{.004\cdot990^2}{2\cdot d\cdot\pi\cdot0.00285^2}\approx \frac{77}{d}\text{ Megapascals (MPa)}$$

The farther away the gun, the less pressure exerted. With simple algebra, we can find that you would have to fire from just under 2 cm away to reach a breaking pressure of 4 GPa.

This is only an approximation since these calculations don't include angle of impact, thickness of armor, ablation effects, the liquid characteristics of metals at high speeds and small time frames, tungsten at high speeds, possible pyrophoric effects, and so on.

Turn it up to 11

So far we've been talking about common mantis shrimp armor. Cool. Let's turn it up to 11 by replacing whatever carbon/calcium materials are in their fists for carbon nanotubes. Given that the theoretical maximum for carbon nanotubes is approximately 100gpa (about 25x our baseline), replacing a substantial portion of the default fist matrix should yield impressive strength gains. I'm no materials engineer so I can't prove it. I only play one on the internet.

Answer 2

Good News Everyone! We already have a natural armor that can resist bullets.

I introduce to you the humble Abalone.

After millions of birds pecking at these things trying to get to the soft, gooey interior, they have evolved the best shell currently known to man. These shells have literally evolved to withstand concentrated, rapid forces.

If you crush and glue 2-4 shells together, you can make a little 1-inch super shell. This super shell can literally withstand bullets. It accomplishes this by having a highly ordered shell. If you zoom in, it looks like a bunch of little bricks in a brick wall, whereas other shells look like a bunch of little sticks randomly glued together.

This is still the subject of research of many material scientists, but I do know that the NSF Center for High Voltage/Temperature Materials and Structures, which draws members from Denver University, University of Connecticut, and University of Illinois at Urbana-Champagne, and Michigan Tech., are actively looking into this. Sadly, I don't have the exact data right now, and I don't think they've published any yet, but unofficial reports show these layered shells do withstand bullets from low-to-medium power firearms, and shows promise of even withstanding higher-powered firearms.

When they do break, they crack, but mechanisms similar to bone re-growth could be used to help repair it. Alternatively, a creature could have "abalone-inspired" plates which regrow after a particular amount of time.

While these are not currently made from the air, the elements needed are biologically available. These little mollusks may be the key to better bullet-proofing in the very near future.

Answer 3

All of the answers that I've skimmed over are really good, but there's one fatal flaw to all of them. When I was in Army Basic training in 1997, we used the M16A2. The standard round for that was the green tipped armor piercing 5.56mm round.

For demonstrations purposes, the drill sergeants filled an empty steel ammo box full of water and shot a hole completely through it, including the back side.

https://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO#United_States

I'm assuming that "US standard issue rifle" means US military.

Things have changed since 1997, but I would assume that current military weapon standards retain the armor piercing capability. I'm not saying the M16 rounds or the rifle rounds of today can pierce a tank, but could pierce a vest.

https://en.wikipedia.org/wiki/M16_rifle#Terminal_ballistics

That link states multiple penetrations stats for the M16, with the (I personally think) most interesting stat being the "31 layers of kevlar". This doesn't state whether the test were using the armor piercing round, but it seems like it.

As good as even @Green's answer is, I don't think even the mantis shrimp claw could withstand armor piercing bullets.

The carbon nano tubules might have a fighting chance, though. I remember a book entitled "Sentenced to Prism" that talked about silicon based life forms of a massive variety. A quick Google says Alan Dean Foster is the author. One of my favorites, and it talks about organisms that can take a beating, lasers, and I think even bullets with a variety of defenses for each. It's a great read, so you'll probably enjoy "researching" that book some.

Good luck with all your research and I hope you find something worth using!

Answer 4

Carbon nano tubes!
If the atmosphere has a lot of CO2, say from volcanoes, pollution, or whatever, you could suck it in, break the carbon oxygen bond, keep the carbon and release the O2. Then you take those carbon atoms and string them along into long chains, form those strands into tubes, and now you have a carbon nano tube. Then you can take lots of those tubes and weave them into a thread. Take lots of threads and weave them into a very strong cloth.
It probably wouldn't be all that fast though.

For a creature to do it using biological means isn't all that crazy, as lots of bacteria use chemical processes to break molecular bonds, and instead of weaving the fibers into a cloth it could embed them into it's skin to toughen it. This would be a gradual process that starts at birth as skin cells form, and the older it got the thicker and tougher the skin would grow.
If the skin is damaged, new tissue would grow to heal the wound, which would have new carbon nano tube strands, and the scar tissue would be tougher than the original skin.
Our body armor has reinforcing ceramic plates in key locations to stop blows to soft organs.
This creature could easily do the same thing with bones like ribs to absorb and shield the kinetic energy. They would also be self healing if a bullet is able to damage one.

One interesting part of this is that if the creature acquires it's carbon from CO2 it breaths in, it could potentially recycle the CO2 from it's own exhalations, which means that it could potentially hold it's breath for a very long time.

Answer 5

I can't satisfy all the requirements of the OP, but here is a partial solution. A naturally occurring fiber that is capable of being used to create a bullet stopping armor is SILK

Silk has a very high tensile strength and is elastic. It is naturally spun by silk-worms. In the real world, the silk fibers sourced from silk-worms needs to be spun into fabric, which is then tailored into a protective bullet-proof vest. So called Dragon Silk is already under development for bullet proof vests for US military.

The use of silk based fabric for armor is actually old. However, with modern genetic engineering technology, the genetically modified silk-worms are capable of stopping bullets.

There are two ways in which this would work on a 'natural' setting:

1. Symbiosis : The creature has a symbiotic relation with silk-worms, that spin several layers of their silk fiber around the creature. This provides the creature with a armor. The worms do this continuously, so the armor is regenerative even if it is partially damaged.

2. Stem cells : The genes of the creature as spliced with that of silk-worms such that the skin of the creature creates this silk-fiber. Over time the skin of the creature acquires several layers of this fiber that gets inter-meshed, to serve as an armor that protects it.

The atmosphere requirement isn't pertinent here. But the silk based armor is a 'realistic' technology that is currently under development and therefore a plausible option.

Answer 6

Do you need armour that stops a bullet like a steel plate, or armour that stops death even if there is some injury, because if the latter you just need a high-tensile fabric 'skin' that has enough give to it to absorb impact.

Old Mongol horsemen used silk shirts to defend against arrows - they worked even though the arrow would hit and stab into them, it wouldn't penetrate the silk and the arrow wouldn't do much damage. Kevlar works in much the same way - the fabric doesn't get cut through and the bullets cause only bruising damage.

So a creature with tough, but relatively loose skin with a good layer of blubber behind that (kevlar vests flex by up to 4cm apparently) would be quite safe, to a point.

An alternative would be a creature with a subdermal layer of fat made of custard (or something similarly non-newtonian). Always beware the custard-monsters!

Answer 7

All answers on this question are measuring against a direct perpendicular impact. I would expect a sticky coated armor that would present a geometrically angled surface might have some effect on slowing down a rifle round enough that there would be little penetration. Try to develop an completely inelastic collision with angles to create lateral forces and friction to reduce the penetration vector. It might take a period of time for the atmosphere to re-coat the armor with this adhesive goo or to realign the geometric plates.

Answer 8

How about steel? Steel is Iron and Carbon, in theory an engineered lifeform in a reasonably metal rich environment could have a bark-like growth of steel in place of its dermis, this material grows from the inside like tree bark, being relatively inert in it's outer layers. Life on Earth can already suffer from excessive Iron, it caused a disorder called hemochromatosis where excess Iron from dietary intake mineralises in the blood causing organ damage. This creature does the same thing, re-mineralising ingested Iron but only in it's skin and on purpose, this creature would have enhanced Iron absorption mechanisms and possibly also use an Iron, rather than Calcium, based skeletal chemistry to simplify its Iron absorption pathways (most vertebrate life on Earth has digestive chemistry geared to absorb Calcium preferential to Iron). Sorry I don't know how thickly it would need to be plated in steel-bark but it would be a continually growing and incrementally shedding armoured shell.

I feel like I missed something so let me know if you need anything else.

Answer 9

Building on the idea of an earlier answer, multi layer armour.

Layer 1: outermost; a tough flexible sheet, possibly some sort of strong leather, that can bend slightly. Protects the inner layers from superficial damage; allows some freedom of movement.

Layer 2: first inner layer. Some gel like substance. Slows down the bullet as it passes through and disperses the energy of the bullet hitting the third area.

Layer 3: plates of ceramic composite (bone or chitin). Plates instead of a single large plate to allow wearer to move. The bullet will shatter the plate it hits, but the energy of the shards and the reaction on the bullet will be absorbed by layers 2 and 4.

Layer 4: a thinner version of layer 2. Prevents shrapnel from forcing its way through the last layer and injuring the wearer.

Layer 5: Silk or leader inner armour. Absorbs any remaining momentum and acts as a framework on which to build the other layers.

The problem is that any armour thick enough to stand up to an automatic rifle is going to be too heavy to wear. What this method does is to treat the incoming bullet as the tip of a wave and try to refract as much of it away as possible. Deflection instead of blocking. It probably won't stand up to a shot at centre mass, though.

Answer 10

Graphene

Lee and colleagues devised a new miniature ballistics test to test graphene’s mettle. They used a laser pulse to superheat gold filaments until they vaporised, acting like gunpowder to fire a micrometre-size glass bullet into 10 to 100 sheets of graphene at 3 kilometres per second – about three times the speed of a bullet fired from an M16 rifle.

The team found that graphene sheets dissipate this kinetic energy by stretching into a cone shape at the bullet’s impact point, and then by cracking outward radially. The cracks are one weakness of single-layer graphene, Lee says, but it nevertheless performs twice as well as Kevlar and withstands 10 times the kinetic energy that steel can. Using multiple layers of graphene or incorporating it into a composite structure could keep the cracks from spreading, too.

Researchers have been studying graphene as armour for some time, but Lee’s is the first paper to describe just how the material absorbs kinetic energy. Sound waves travel three times faster through graphene than they do through steel, which means material far beyond the impact point can quickly absorb and dissipate its energy – effectively slowing the projectile down and helping prevent its penetration. What’s more, the microbullet methods Lee developed could be used to study other high-performance materials in extreme conditions.

https://www.newscientist.com/article/dn26626-bulletproof-graphene-makes-ultra-strong-body-armour/

Better yet, it is self-repairing, too! Just add free carbon atoms and they will snap into place in a broken lattice.

Answer 11

All prior answers suggest the direct route of materials with high strength.

I suggest an alternate solution, based on inertia. Any projectile has a certain mass, and it imparts momentum from that mass onto its target upon impact— No matter how fast it's going, it can only penetrate so far before it's shed enough of its momentum into the struck material that it stops. And because the amount of inertia it sheds per unit time is proportional to its speed, the approximate penetration depth is the same for all high-speed impacts.

Therefore, I believe the idea form of biological body armour for stopping bullets may be body fat, or even water (in the form of a jelly).

It looks like most US rifle bullets are around 5cm long. If we assume they're made out of solid copper at 9g/cm³, we can calculate the approximate depth of fat or water (~1g/cm³) that would be required to equal its inertia:

D = 5cm*((9g/cm³)/(1g/cm³))

= 5cm*9

= 45cm

Since this is the theoretical ideal case, we can multiply it by two or three times to give a more realistic margin. Doing so also yields figures that are consistent with what the Mythbusters found when they shot a variety of gun types into a swimming pool.

A meter of fat and water sounds like a lot to lug around. But when you compare it to the size of creatures like elephants and whales, and how much blubber they already have just for thermal insulation, it's not really that much. If the armour is concentrated at a single area like a camel's hump, they could also use it as a shield by pointing it towards danger.

Crucially, this solution also has a wide variety of benefits that are unique to a biologically synthesized armour:

• It doubles as an energy reserve. Since water is essential for life, and fat is a very compact calorie source, armour made out of water (jelly) and body fat also serves a purpose even when it's not under attack. Maybe the organisms in question already had exaggerated, camel-like reserves of fat and water because they live in a desert, and they simply evolved to expose it as armour when under attack. Maybe they're scavengers who feed on the scraps left behind after a war; They build up fat to use as protection during times of conflict, and during peacetime, when there's less food for them and there's no need to fear bullets, they gradually digest their stored fat and water.

• It can be grown almost instantly, and for free. Because there are no special structures involved— no nanotubes, steel plates, woven silk threads, or special shells that must be grown— the organism with this kind of armour does not have to spend nutrients, calories, and genetic complexity on constructing an organ whose only purpose is to be destroyed.

• It is arguably immune to damage, and can be repaired almost instantly for free. Likewise, because it's not the structure of the armour so much as its sheer bulk that gives it its protective properties, it will continue to function even after it's been all shot up. Healing is also easy due to its simple structure, and even in the event that it gets severed from the organism's body, they can just eat it and have it digested and restored within a couple of days.

• It requires no special nutrients or minerals. Since water and fat are both essential chemicals for basically all known life, any organism is already capable of finding, processing, synthesizing, and growing them. Water can be pulled from vapour in the atmosphere, and fat can be constructed out of CO2 (like in plants, I think).

• It can synergize with other protective strategies. Since defeating the projectile takes place over the entire depth of the fat and water, the fat and water armour could offer any level of protection in proportion to its thickness. This opens the door for some unique composite armour growths. For example, a thinner layer of easy-to-repair fat and water armour could slow down a projectile just enough that it's then stopped completely by a simple bony plate, or you could have hard but simple chunks of denser material embedded at the surface of the fat and water layer to break up a projectile and let it dump its momentum more quickly over a shorter depth (kinda like a Whipple Shield). This allows for optimized combinations of easy reparability and minimized bulk, from the fat and water and the plate armour respectively.

• It makes more evolutionary sense. Any brute-strength armour that can resist bullets is likely to be extremely biologically costly to construct and maintain. Furthermore, the fact that armour is inherently a sacrificial tool means that even an unsuccessful attack will probably incapacitate the organism for long enough that they'd starve to death while trying to repair their armour. The gain in defensive ability simply may not be worth the cost in calories and genetics. Under circumstances like these, Evolution tends to give up on making super-powerful individual creatures, and instead create individually weaker creatures that overwhelm survival threats by making thousands of babies. In order for "natural" bulletproof armour to evolve and persist, it needs to be simple enough and calorically inexpensive enough that the costs of its growth and repair do not outweigh its benefits for survival. I believe bulked masses of extremely simple biological material may be the best and likeliest way to achieve this.

Answer 12

Armadillos.

There is at least one documented case of an armadillo being resilient to pistol shots:

https://www.huffingtonpost.com/entry/texas-armadillo-shooting_us_59838ae2e4b08b75dcc5f622

(.38 shots fired at armadillo, animal was able to walk away, shooter got severely injured by ricochet).

Answer 13

An amour with many layers. As each layer will reduce bullet speed. There are examples in the animal kingdom where animals grow layers of hard shells or use natural resources like sand, etc. to create armors which can stop even a bullet.