Tempur and Ballistic Polymer

[Luckyorwhat]

Can;t find anything on MatWeb, maybe someone here has more information on either of these? Even a similar material that could be found on MatWeb would be appreciated.

 

B.P.

 

http://www.justshootmeproducts.com/

 

 

Tempur

 

http://www.tempurpedic.ca/en/the_material/about_tempur.php

[TTK Ciar]

the ballistic polymer is a head-scratcher, but a little research suggests tempur is a polyurethane-based elastomer foam of proprietary formulation. It's probably patented, so you should be able to find something here:

 

Patent search: "elastomer foam viscoelastic"

 

-- TTK

Edited April 1, 2007 by TTK Ciar

[Luckyorwhat]

Thanks for the tips, unfortunately Matweb only had 1 hit for viscoelastic. I've ordered a sample, just the same. It may sound silly, but on another forum some people are curious about what happens if memory foam is shot. I hope to get a more detailed name of the composition from the distributor.

 

Could you advise on how to determine thickness or mass efficiency?

[TTK Ciar]

Could you advise on how to determine thickness or mass efficiency?

I have had good luck with particle board as a witness material. It is fairly regular in composition, and is soft enough that precise measurements can be made -- if your measurements are off by 2mm, say, and you measure 5mm penetration into steel, then your error is ~40%, but if you measure 250mm penetration into particle board, then your error is only ~1.5%.

 

Use a firearm and penetrator with a well-documented RHA penetration rating (say, 150gr FMJ 7.62mm NATO). Fire six shots, about a foot apart, into a ~2-foot thick stack of tightly-bound particle board oriented such that the boards are facing you (the penetrator strikes perpendicular to the face of the top board, and penetrates multiple boards). The exact depth will depend on the composition of the boards, your distance from them, bullet wobble imparted by your gun, and other things. Normalize this against the expected RHA penetration (4mm for 7.62mm FMJ, so if you penetrate 120mm your penetration ratio is 30.0). Eliminate the least-penetrating and most-penetrating samples, and average the rest. This will be your baseline penetration.

 

You should be able to obtain the density of your specimen materials (the foam) from matweb or the manufacturer. If not, though, then you need to measure the exact dimensions and weights of your specimens before shooting them to obtain their densities. In any case you need to measure their thickness so you can compute their thickness efficiencies later. Their densities will allow you to convert from thickness efficiency to mass efficiency.

 

Set up your particle boards again as before (fresh ones, but of the same composition, and preferably from the same batch) with six specimens glued to the outermost board, spaced one foot apart (measured center to center -- so if your specimens are eight inches wide, there will only be four inches between their edges). I like using a polyurethane (like Gorilla Glue) around the edges of the specimen only, so that the bullet doesn't have to penetrate any of the PU. Put a bullet through each specimen, as close to their centers as you can get. Measure the residual penetrations (from the outer face of the outermost board to the bottom of the craters -- do not measure from the outer face of the specimen!). Again, I like to eliminate the most- and least-penetration samples.

 

Use the difference between the baseline penetrations and residual penetrations to calculate the thickness efficiency of your specimens. If your baseline average penetration was 120mm, and your average residual penetration was 75mm, then the specimens were "worth" 45mm of particle board. Normalize this to eRHA by dividing 45mm by your penetration ratio (30.0 in the above example, which would give 1.5mm eRHA).

 

Divide this eRHA by the thickness of your specimens to get a thickness efficiency. If your specimens were 300mm thick, then your thickness efficiency would be 0.0050. To convert TE to ME, multiply TE by 7.86 (the density of RHA) and divide by the density of your specimen material. So if your foam had a density of 0.010, your ME would be 0.0050 * 7.86 / 0.010 = 3.9 (I'm not confident enough in my measurements, or in the consistency of my witness material, to quote more than two sigfigs).

 

Obviously if you have the money to spend you can use this same approach with a better rig .. HDPE instead of particle board, perhaps, and more than six sample shots (according to my statician friend, 200 samples are really needed for an ironclad claim, but six is good enough for my limited budget).

 

I'm an amateur, so take this all with a grain of salt. The process described was gleaned from reading IJIE articles, and practice.

 

Good luck!

-- TTK

[Luckyorwhat]

Thanks, I'll do that - except with a different caliber. I'll update when the sample is received.

[TTK Ciar]

Thanks, I'll do that - except with a different caliber. I'll update when the sample is received.

Good luck! :-) if the caliber you choose has an unknown eRHA penetration capability, then you can estimate it by testing penetration into Lexan polycarbonate (which has a known TE of 0.32). eRHA ratings are all approximations and of limited viability, so too much precision isn't terribly necessary.

 

-- TTK

[Luckyorwhat]

I'm a little embarassed to say I don't own a 9mm yet, but I'll try with 7.62x39 lead-core. If the indoor range will let me I can test up to 50m with 5.56 55grn fmj and .45 ball.