Kevlar in Spacecraft

[Gargamel]

On 11/19/2018 at 1:44 PM, 4472TJ said:

this looks quite similar to the sort of stuff used in space suits

Just because it looks similar, doesn't mean it's the same.   And those are not pics of Kevlar, but of a similar material.  They were just using that to show it is a fiber/cloth, not a putty. 

[munlander1]

Could Kevlar be used to give additional shielding in a composit shield? How much Kevlar would you need to stop bullet at orbital velocity?

[kerbiloid]

2 hours ago, munlander1 said:

How much Kevlar would you need to stop bullet at orbital velocity?

If both you and the gunner are orbiting in the same direction, I guess as much as on Earth.

Edited November 24, 2018 by kerbiloid

[Gargamel]

16 hours ago, kerbiloid said:

If both you and the gunner are orbiting in the same direction, I guess as much as on Earth.

But if they're not...

I'd almost want the bullet to pass clean through, with it only making two bullet sized holes.  With armor, and that's what we're basically talking about now, you can get spalling, which is the fragmentation of the wall into shrapnel.    That may cause a lot more damage, to people and interior components, than two little holes would.  Yes, the parts/people immediately inline will get damaged, but explosive spalling inside a spacecraft seems worse to me.   Not only can it cause immediate damage, but the particles can also get inhaled very easily.  As we've recently seen on the ISS, small holes are easily fixed.  

Even if the bullet is caught, the way kevlar works is by deforming to absorb and dissipate the energy of the projectile.   That alone may cause damage to interior structures, and the lack of holes might make it difficult to fix as easily.  I know I have treated people in the trauma ED that have been shot wearing vests, and some of them still have broken ribs, one even punctured a lung from it. 

[kerbiloid]

32 minutes ago, Gargamel said:

But if they're not...

So, if the collision speed = 16 km/s?
It's ~1 MJ of energy (~100mm anti-tank projectile) and ~150 kg*m/s of impulse (~20 mm projectile).

Then kevlar means something just because it has significant inner friction and can quickly transform kinetic energy into thermal one, dissipating it around.
It's weak agaist impulse (not energy), slow penetrators, and it decays at ~>500°C.
So, they use it just against the low-impulse projectiles like pistol bullets, stone crumb, and shrapnel. But hardly against the rifle bullets, knives, and flame.

You would use a tank armor with thin kevlar layer inside to stop the secondary shrapnel.

***
(Just because already have googled, but not because of the question:)
http://www.dupont.com/content/dam/dupont/products-and-services/fabrics-fibers-and-nonwovens/fibers/documents/DPT_Kevlar_Technical_Guide_Revised.pdf

[Thor Wotansen]

On 11/24/2018 at 11:13 PM, Gargamel said:

I'd almost want the bullet to pass clean through, with it only making two bullet sized holes

That's not how bullets are generally designed to work.  The general idea is that you want the bullet to release as much energy into it's target as possible, which it won't do if it makes a neat little hole.  Kevlar and other soft types of bullet resistant vests use this to their advantage, since most bullets designed to be used on soft targets are hollow point or similar, that expand on impact in order to maximize the amount of kinetic energy they release.  The kevlar vest's job is to stop the bullet from penetrating and the vest has thick padding to distribute the impact over more of the body of the wearer.

[Gargamel]

On 11/26/2018 at 9:51 AM, Thor Wotansen said:

That's not how bullets are generally designed to work.

Depends on the bullet really, some are designed to fragment, some are designed to stay whole.   But in this case, being the recipient of said bullet, I'd much rather them stay in one piece.    But I'm also extrapolating that, in this case, "bullet" is just a place holder for some high speed, medium mass object traveling at orbital velocity. 

[kerbiloid]

A projectile.

[DDE]

On 11/24/2018 at 10:23 AM, munlander1 said:

Could Kevlar be used to give additional shielding in a composit shield? How much Kevlar would you need to stop bullet at orbital velocity?

It’d be worthless. At orbital velocities, a completely different set of impact effects is in play, and the material used is often quite irrelevant.

What you need is a Whipple shield.

[Gargamel]

On 11/30/2018 at 5:15 AM, DDE said:

Whipple shield.

Which comes full circle, as some Whipple designs do use Kevlar. 

Quote

Whipple shields that have a filling in between the rigid layers of the shield are called stuffed Whipple shields.^[4][5] The filling in these shields is usually a high-strength material like Kevlar or Nextel aluminium oxide fiber.

 

[Kerbinchaser]

You know how people in movies will be scanning the horizon with binoculars, pass over the target, and then shoot right back on it? 

Yeah, I just did that with this thread. I was scrolling down, minding my own business, when I saw the word "kevlar" and decided I had to read it. 
Once again, it's a bunch of Science nerds talking about space and the possibility of using a substance in a vacuum.

I love this forum. 

 

Edited December 3, 2018 by Lo Var Lachland