Aug 17, 2011

Picatinny engineers develop versatile warheads

PICATINNY ARSENAL, N.J., Aug. 17, 2011 -- The shifting dynamics on the battlefield can inject variation and unpredictability at various levels.
For instance, the impact of artillery bombardments can depend on multiple factors, including the nearly infinite ways that a shell can break apart on detonation to affect its intended target.
When projectiles such as a 155mm artillery shell explode, the resulting fragments can vary dramatically in size -- from harmless, dust-like remnants to much larger pieces that can inflict great damage.
This type of "natural fragmentation" -- with such a wide variation in fragment size -- tends to make the result of shelling unpredictable and inefficient.
"When you're targeting certain things like personnel or vehicles, you're looking to get a fragment that's a particular size," said Peter Rottinger, a mechanical engineer at Picatinny Arsenal's Armament Research, Development and Engineering Center.
"With natural fragmentation, you may get some fragments that are not going to be lethal and you may get some fragments that are over-lethal, like four times the size that you really needed to defeat that target, so it becomes inefficient," Rottinger added.
Designing warheads better suited to specific targets because they produce a more consistent shell fragment is one of the goals being pursued by Rottinger and his co-workers at the Force Protection and Explosively Formed Penetrator Branch here.

Research into "single mode" fragmentation, initiated by Project Manager Combat Ammunition Systems (PM-CAS) at Picatinny, was aimed at achieving a design that would create shell fragments of relatively equal size consistently.
Later, under the auspices of another organization, the research progressed to a "multi-mode" design. With this design, Soldiers could choose between either of two sizes of fragments by making an adjustment through the fuse assembly of a projectile.
On detonation, the fragments are dispersed according to a desired pattern, depending on whether they are intended for soft targets with smaller fragments, or material targets like trucks that require larger shell pieces to be effective.
According to Rottinger, the advantages of the multi-mode warhead are enhanced lethality and greater effectiveness against a wide range of targets.
Also, by eliminating the need to maintain large supplies of single-purpose munitions, controlled fragmentation is expected to reduce overall Soldier load and streamline logistics.
Moreover, test results show that the technology is scalable. Testing of projectiles ranging in size from 155mm to 40mm has shown promising results.
The Joint Services Small Arms Program provided funding for research on the 40mm grenade.


Early research on a single-mode projectile was methodical and tedious.
"Once modeling and simulation was complete, we came up with various candidate designs," Rottinger said. "We had limited funding and you can't test everything. So you go and pick what you think the best solutions are going to be."
Research into a "multi-mode" shell that could produce two different sizes of fragments yielded various technologies.
"Multi-mode lets you change fragment size on the fly, so if the Soldier knows that he's going to be going after personnel, he can set the warhead to produce smaller fragments," said Rottinger. "You get more fragments out there and you get higher efficiency."
The development of technology such as controlled fragmentation evolves with modeling simulation, testing and analysis. Yet determining whether a technology works is just part of the overall process of eventually sending new armaments into the battlefield.
"A lot of people don't want to get something new out there unless it's going to save them money in the long run," Rottinger noted.
"There are some advantages to having multi-mode warheads because you can reduce your logistics. Instead of having to have multiple rounds to take care of the mission now you can have a single round."
As greater scrutiny is given to controlling costs in defense spending, new technology must not only be effective but affordable and relatively easy to make. Yet certain spending up front may be unavoidable.

"It's hard for us to look at cost early on," Rottinger said. "When you're looking at research and development, everything is expensive. So you have to develop a technology and make sure the technology gives you the effect that you want to see, and then you can do more research into the producibility of the item."
"And that's basically where we are in this program now," explained Rottinger. "We're at a point where we have to show that we can make them more affordable so they are more attractive to the customer."
Henry Hsieh, a mechanical engineer at the ARDEC branch, said that even from the early stages of research, constant thought is given to how to achieve efficiency and reduce costs.
"We try to use commercially available products and existing manufacturing techniques," he said.
Driving down costs involves looking at various materials that could be used along with the different manufacturing techniques.
Rottinger said drawing the expertise of manufacturers helps to expand the number of possible options.
"The manufacturer is going to have much better ideas of what's possible and what tools are available," Rottinger said. "We're always bouncing ideas off of them.''
"Commonly used techniques such as stamping and rolling could be used to meet the requirements and shorten the product cycle," added Hsieh.
Experimenting with various techniques can yield dividends over time.
"As you become more familiar with the technology, you start developing better tools and better ways to do this so that you can speed it up," Rottinger said. "If there is a real strong desire to get it out fast, we can do it." 
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