# The plausibility of tungsten reinforced steel Composite Metal Foam (CMF) as body armor

Hi everyone I would like to ask if this material is suitable to be used as body armor like kevlar, as I am planning to use them as armor for my novel. What are the drawbacks to this? Could the armor resist, stabs from spears or swords or arrows, can it withstand blunt impact? It seems that this material can obliterate bullets as per this video. https://www.youtube.com/watch?v=dRpyM3a4Wj8.

I just want to know if this material can withstand balistic impact and thrust and slashes as well. An all encompassing body armor of sorts. It won't go up against lasers just material projectiles.

• the term you are looking for is CMF composite metal foams, without emphasizing this many may not grasp that is what you are talking about. – John Aug 6 '18 at 5:40
• what is this armor going up against you say spears and arrows but you are also adding bullets so are we taking about muskets here. if its modern times or even the future we will need more details (is he going to take a bullet from a tank small arms rifle rounds arrows). – Creed Arcon Aug 6 '18 at 6:44
• Are you sure you aren't confusing Tungsten with Titanium? Titanium body armor is currently being used by the US military as body armor. It's light, and strong, but incredibly difficult to process. Currently we compress Titanium powder into a plate insert for vests. – Stephan Aug 6 '18 at 15:35
• With your CMF armor, why is he up against sword, spears, blunts and arrows and bullets? metal foams where introduced in 1926 (based on wikipedia search), What kind of bullets? uranium depleted bullets from A-10 bombers? .50 cal? or just 9mm? What's the story behind if I may ask? – Mr.J Aug 7 '18 at 7:06

Simple Answer: Is it plausible? Yes

Not so simply answer: yes it is still plausible, but it is probably not going to be practical or cheap:

Practicality for Armour:

As a base metal Tungsten is fantastic as dealing with heat,, but its also very heavy and for its weight it is quite brittle. now turning that into a CMF, would reduce the weight but it won't stop its brittleness being an issue, while it is still metal and strong, it probably won't stop a bullet.

Now when you mix it with steel some of those issues go away, it'll stop a bullet. but the added advantages of Tungsten aren't really there you would reduce the weight loss, but not really add any benefit, and add that compared to steel, tungsten is really really pricey. you adding a lot of extra cost as well

The current price of tungsten is approximately US \$19.85 per pound compared to steel, which is about \$0.45 per pound so it would depend on the ratios used in making the armour.

It would very easily be able to resist Stabs, and arrows, but plain on Steel Metal Foam could do so equally well, (possible a little better) and be lighter

That video appears to be Aluminium or Steel, which are a lot stronger than Tungsten, and while it looks impressive, when you watch slow motion videos of bullets hitting steel plate pretty much the same thing happens

But i had to watch it at work, with the sound off, so if it was spoken saying what it was then please correct me

https://www.youtube.com/watch?v=QfDoQwIAaXg while this video shows materials other than just steel, its a nice video to watch, especially the rifled bullets being peeled apart on impact along the lines of the rifling

the benefits of CMF is its strength compared to its weight.

However

if it was being designed to go up against energy weapons, plasma laser etc, where the damage done is by imparting heat into the target faster than the target can dissipate that heat then it would be a very very good materiel to use! Tungsten's greatest ability is its extremely high melting point and its ability to dissipate heat.

Edit: Also worth noting, that CMFs are quite advanced armours, and yet going up against swords and spears... are you trying to reform the British Empire?

• + 1 for detail, i had the same issue with the OP adding swords and arrows into the mix (that's why i will not answer until he updates) also what do you think of nano-carbon plated amour as a replacement over steel? – Creed Arcon Aug 6 '18 at 9:44
• @creed, Cheers, it seems a bit odd, but depending on the setting it could work. Carbon nanotube reinforced Titanium is probably the best solution, if nothing else its easily the coolest sounding! but replacing the steel and leaving the tungsten... it could work. but once again we're making this armour incredibly expensive – Blade Wraith Aug 6 '18 at 10:41

As a materials scientist, this is a rather interesting question. I'm not going to say it's implausable, just list some of the issues I forsee with this. Here is a list of the concerns I have: Processing, Alloy choice, and impact resistance.

Let's start with processing. First, we need to understand how these are actually made. There are two main methods. The first of which is to use a dissolvable place holder material. This would imply whichever group is making this has a sufficient understanding of polymers (plastics and other large organic molecules). The second method is to inject gas at very high pressures during the solidification process. I've heard things like 500 atm quoted but can't find a source. These kinds of pressures have been effectively impossible to achieve without the invention of the jet engine. So you're asking if you can make it into armor which has historically not been a cast material which reduces the viability of this material.

Secondly, let's discuss alloy choice. We have to be careful which gas or dissolvable material you use depending what alloy we want to use. Steels are especially sensitive. Now, you mentioned tungsten. Not to discourage you, but tungsten in my opinion is a poor choice for base alloying material. Tungsten, while being classed as a metal behaves closer to a ceramic in many cases. It's easy to embrittle which would be an issue for armor. That being said, a steel with tungsten as an alloying element would be beneficial. This strengthens the material without losing fracture toughness. I won't get into the details about why, but you could look up alloying elements for steel if you're curious what others do.

Finally, we need to determine how impact resistant this material is. The material holds up well against bullets as bullets are often softer metals because they tend to be heavier. But keep in mind that bullet was firing at a block of material. The story would be very different if it was a plate of this material. The fracture toughness of this material should be drastically lower than that of the respective alloy because the pores allow for cracks to form. There's just generally less material is another part of it. So if you were to get hit by a sword or blunt weapon, it could have serious consequences for the wearer. It would not be unreasonable to expect that the material would plastically deform (give out) and likely fracture into the person. One strong hit and you'd be done. With that being said, my material property analysis is mainly speculation. I don't have access to the information I'd need to find out if what I'm saying is true.

So those are the things I think you need to keep in mind in terms of viability. Let me know if you have any comments or questions

• The fracturing of the material would dissipate a lot of the impact, similar to ceramic plates in bullet resistant vests, so although any followup attack would be met unprotected, a single blow would be protected – Blade Wraith Aug 6 '18 at 15:49
• +1 thank you for this. I added swords and spears just so that i would know if it would be an all around body armor that can withstand slashes and thrusts as well as balistics. It was merely hypothetical because given that an enemy would know the material the body armor is made of, he could switch weapons for major damage. – Harbinger Aug 6 '18 at 17:36
• I just re read the links where i got my idea from. It seems there is a cost effective way of making the material: "encasing pre-made spheres with a powdered version of the same material, or suspending spheres made of a material in one with a lower melting point." – AFSANEH RABIEI / NORTH CAROLINA STATE UNIVERSITY – Harbinger Aug 6 '18 at 17:56

Drawbacks:

1. Weight. (After all, it's steel...)
2. Cost. (Tungsten is expensive. Ditto metal foams.)

Benefits:

1. Rule of Cool.
2. It's "near future plausible".

Thus -- within reason -- you can make it perform however you want it to perform, giving it whatever capabilities and weaknesses you want.

Tungsten isn't really something you use anywhere where weight might be a concern. It's 2/3rds the density of lead and 3 times that of steel. Tungsten's real benefits are its good high temperature properties, extreme stiffness, hardness, and density (for ballasts). None of those properties come into play with body armor, the property you should be looking for is toughness, which tungsten is not particularly known for (although it could still be used in small quantities as an alloying component). You would be better off with different materials. If you want something fun look into metallic glasses, some of those can be extremely tough.

• Note the OP is discussing composite metal foams, which don't behave exactly like the the metals in a bulk form. It is also much lighter. – John Aug 6 '18 at 5:40