ATAC and the Armor/Anti-Armor Program

Armor/Anti-Armor

The Rand Corporation, E. I DuPont de Nemours, Honeywell, Inc., Battelle Washington Operation, Textron Defense Systems

chief concern driving the cur- tors and electronics), materials proper- challenge industry in the key technolo- rent U.S. armor/anti-armor ties (especially at high strain rates and gies by making the research, develop- program is that the Soviets extreme pressures), and computer mod- ment, test, and evaluation stages of the Ahave a significant lead over eling. Further, the precision required for national program highly competitive. the United States in tanks and antitank nuclear ordnance has forced the Labo- The strategy has been implemented weapons (see “A Comment by General ratory to explore these technologies at by breaking the core of the Armor/Anti- Starry”). Moreover, simple solutions in very detailed and precise levels. Armor Program into three major ele- armor and anti-armor technology have Throughout the 1970s Los Alamos ments: the Blue Teams, the Red Design already been implemented, so it may contributed to Department of Defense Bureau, and ATAC. The Blue Teams no longer be possible to find a “quick conventional munitions. For example, consist of contractors who are develop- fix” that will catapult the conventional we developed a uranium alloy to serve ing armor and antitank weapons. These U.S. forces to a decisive lead over the as an armor-piercing round for the Air contractors are large industrial corpo- Soviets. The problems are complex and Force. The material proved so effective rations that have enlisted universities, the science sophisticated enough that it became a standard for large-caliber national laboratories, and other corpo- we cannot depend on small, incremental Penetrators. We also collaborated with rations as subcontractors to help with improvements. We must base new solu- industry and Navy laboratories to solve their competitive efforts. The first phase tions on a better scientific understanding a propellant safety problem that threat- of the program involves about 130 ma- of materials and their behavior under ened the Trident system. This last effort jor contractors selected from an original ballistic conditions. led to the joint development—by Los field of over 400 companies. As a result the national Armor/Anti- Alamos, Lawrence Livermore National The Red Design Bureau—headed by Armor Program, although spearheaded Laboratory, and the Air Force Rocket Battelle Memorial Institute in Colum- by DARPA (Defense Advanced Re- Propulsion Laboratory-of a method- bus, Ohio was created to design a “So- search Projects Agency), is also a col- ology for testing the safety of solid viet threat” for the competitive stages of laborative effort with the U.S. Army, rocket propellant. One of our most no- the program. The threat is based on an the U.S. Marine Corps, and 130 corpo- table contributions was the long standoff independent evaluation of available in- rations, laboratories, and universities. penetrator, a shaped-charge, chemical- telligence data. In other words, the Bu- A key element in this collaboration is energy weapon that was tested in 1979 reau tries to “think Soviet, ” design what the Advanced Technology Assessment and shown to penetrate more deeply into the Soviets might be designing, and then Center created at Los Alamos to pro- armor than any other such weapon. In- fabricate actual prototypes. These futur- vide the strong scientific base needed terest in the design of this penetrator istic Soviet armors and Penetrators are for high-tech advances in armor and ar- led to more extensive Los Alamos in- used to test and assess the Blue Team mor Penetrators. ATAC serves as both a teractions with Department of Defense hardware. Members of the Blue Teams testing center for new developments and munitions researchers and, ultimately, to do not learn what the threat will be until a scientific resource that all participants the choice of Los Alamos as ATAC. about a month before competitive test- can draw upon. ing. A major impetus for choosing Los The roles of ATAC are, first, to stim- Armor/Anti-Armor Alamos as the Advanced Technology ulate the entire process by transferring Program Goals Assessment Center was history: there technology from Los Alamos to indus- has always been a synergistic and inti- The long-term goals of the national try and, second, for the Laboratory to mate relationship between the Labora- Armor/Anti-Armor Program are to de- serve as a neutral referee in the compet- tory’s nuclear and conventional weapons velop a broad base of expertise in pri- itive stages. Specifically, ATAC helps technologies. In the early days of the vate industry and make that expertise the Blue Team members develop better Manhattan Project, ordnance experts available to the U.S. Armed Forces. On products, and then it tests those products came to Los Alamos to design essential a short-term basis the national program against the threat created by the Red components of the first nuclear devices. also hopes to increase the rate at which Design Bureau. Much of the help pro- The overlap between the design of nu- we modernize armor and anti-armor vided by ATAC comes from two major clear and conventional weapons that was systems until the U.S. can outperform areas of Los Alamos research: mater- established then, and which continues the Soviet Union in the development of ials science (see “Armor/Anti-Armor— today, includes the hydrodynamics of several key technologies. The strategy Materials by Design”) and computa- high explosives, firing systems (detona- devised to accomplish both goals is to tional codes (see “Modeling Armor Pen-

Los Alamos Science Summer 1989 Armor/Anti-Armor

General Research Corporation, Nuclear Metals, Inc., Aerojet Ordnance Co., AAI Corporation, FMC Corporation, Physics International Company

etration”). ATAC is also responsible however, they appeared much more ef- microstructure of the liner are critically for ensuring that testing of Blue Team ficient than expected. In truth, no one important. Additionally, we have found products is performed and evaluated ac- understood how the armor worked. that a specific “heat and beat” fabrica- curately, thoroughly, and without bias. Eventually it was proposed that the tion process for each material has to Our evaluations include recommenda- breakup created a mass of hard, abrasive be followed to achieve the preferred tions for future funding of promising ceramic chips that eroded the penetrator. crystalline microstructure. We had to technologies. Detailed computational and materials explore a variety of these processes ATAC’S effectiveness in the Armor/ research at both Los Alamos and Liv- to select the correct one—an expen- Anti-Armor Program requires that Los ermore confirmed this hypothesis and sive, time-consuming task if done solely Alamos be at the technical forefront of made us realize how to turn the appar- on an experimental basis. We hope to armor and anti-armor research. Thus ent disadvantage to our favor. The goal shorten the task considerably by us- ATAC invests a significant portion of was then to keep fractured ceramic in ing a computer model to predict liner its budget in research on materials sci- front of the penetrator as long as possi- performance based upon various crys- ence and technology, development of ble, causing the rod to erode as it forced talline microstructure. We will make diagnostic techniques, and computa- its way through the rubble. As a result, this information and the modeling code tional research. In addition, Los Alamos how the material was packaged became available to others, including Blue Team has contracted a number of consultants as important as its strength and fracture contractors. In fact, industry has been and universities for help in disciplines characteristics. briefed on the preliminary work. outside the expertise of Los Alamos sci- Only by examining defeat mecha- We are hoping that the same process entists. nisms in this detailed way can scientists evolves for kinetic-energy Penetrators, optimize both the material character- which several Blue Team contractors A Scientific Challenge istics (abrasive chips) and product de- have undertaken to explore. At present, sign (how to confine those chips) to the idea that dominates development of The basic challenge in armor/anti- enhance the desired effects. (See both kinetic-energy Penetrators is simply that armor research and development is to “Armor/Anti-Armor-Materials by De- the heavier the penetrator and the faster understand each problem from sound sign” and “Studying Ceramic Armor it hits the target, the better. However, physical principles and the appropriate with PHERMEX” for a fuller discussion Blue Team contractors are asking them- materials properties. For example, our of ceramic armors.) selves several questions: What mechan- thinking about the usefulness of ceram- The same challenge of’ understanding ical properties should be considered? ics as armor material changed drastically the physics of the ballistic event, the Does fracture toughness give the pene- with an increase in our understanding materials involved, and the effect of trator its ultimate strength? What effect of ceramic material properties and how product design is true for Penetrators. does chemical composition have on this ceramics react physically to ballistic im- An example is the metal liner used in strength? In other words, a better under- pact. chemical-energy weapons. The detona- standing of the physics of high-velocity One of the most efficient ways for tion of a shaped charge moves this liner impact needs to be acquired. This is the armor to defeat a projectile is to turn at the target in such a way that the ma- type of challenge facing the Blue Team. most of the kinetic energy back into de- terial transforms into a high-velocity jet struction of the projectile itself, say by of solid stretching material. To be ef- Current Research fracture or plastic flow in the penetra- fective, the liner must have the proper tor. Ceramics were considered possible combination of strength and ductility to Further advances in the develop- as armor material because they gen- allow it to stretch without breaking. ment of the chemical-energy warhead erally have high compressive strength If one is to achieve a desired liner is a tactically urgent problem that the and are lightweight, two qualities de- performance, criteria—such as the ma- Armor/Anti-Armor Program is currently sirable for mobile weapons systems terial density, the tip velocity, and the tackling with much vigor. Before re- that need tough, light armor. Unfortu- coherency of the jet—must first be de- active and spaced armors were intro- nately, ceramics also tend to be brittle termined. Then the key elements neces- duced, chemical-energy weapons had a and break up easily on impact, which, it sary to those criteria must be identified. number of clear-cut advantages. For in- was thought, would undermine the ma- For instance, work at Los Alamos has stance, the chemical-energy penetrator terial’s ability to destroy the penetrator. shown that selection of liner material, is better at penetrating steel armor than When ceramic materials were tested, design of the charge, and the crystalline continued on page 56

I.os Alamos Science Summer 1989 53 e are behind the Soviets to catch up and frequently as long as fif- in both armor and bullets. teen years to apply the same technology A w That simple declarative in our fielded systems. sentence is what makes the ratification “This is not an indictment of our in- of the Intermediate-range Nuclear Force telligence system. We do gather suf- Comment (INF) treaty a provocative action. It is ficient information on which to make the raison d’etre for the new national in- fairly reliable estimates. In fact, three terest in armor and anti-armor technolo- years ago we had the intelligence com- bv gies. And it was the principal finding of munity make some estimates of what the 1985 Defense Science Board Task was in the ‘bathtub;’ to no one’s sur- Force on Armor/Anti-Armor, of which I prise, those developments are now be- General was the chairman. ginning to appear. “Our Task Force study reported that, “The flaw, instead, is in our decision- in armor and anti-armor systems, the making process. Our system reacts Starry U.S. has been behind the Soviets for positively only when confronted with perhaps fifteen to twenty years, and we hard evidence—a photograph of fielded are falling further behind at an alarm- equipment—and negatively to an in- ing rate (see Figure). Back in 1985, telligence community ‘bathtub’ projec- we considered the problem as one ‘ap- tion. No one in Washington is willing proaching a matter of national urgency.’ to make a decision until shown a picture Today we have crossed the threshold; of a fielded system incorporating new the situation is now a matter for urgent technology; then there will be all sorts national priority. of doomsday and ‘how could this have “The problem is not a lack of tech- happened’ reactions. nology or intelligence data. Scientific “So the first problem our country has journals and other open literature collec- is how we look at the threat. The sec- tively provide a fairly substantial body ond problem is one of technology field- of data from which we can determine, at ing. We are fighting against a natural least by inference, what they are doing tendency of laboratory scientists-even in research and development. at places like Los Alamos—to keep the “However, over time, we find infor- technology at the workbench too long. mation concerning a given technology Of course, they want to keep improv- declining in volume or even disappear- ing the capabilities, But if you allow ing from their literature, Does this mean the scientists more and more time and that the Soviets have given up on a funds, you may end up with a wait of technology? The U.S. has a tendency five to ten years, an expenditure of mil- to believe so. That may be true, but it lions or billions of dollars, and only a is equally possible that they have moved marginal improvement in performance, the technology into full-scale engineer- In other words, a laboratory has no in- ing development. Eight to ten years centive to get the technology out. may pass. Then, all too frequently, “It is vital to have a decision-making we identify what we would call a new mechanism to drive the technology off weapon system on a test track or, in the workbench and into the field. The some cases, being issued to the troops— Soviets have such a mechanism: the a system that fields the so-called disap- five-year planning process. Relentlessly, peared technology. every five years the Soviets transfer “The Task Force called this decline of technology from the bench to the field. information during full-scale engineer- We have-no similar system. In fact, the ing the Bathtub of Ignorance, Histori- Task Force examined thirty of our tech- cally, it has taken us at least five years nology developments and found at least Armor/Anti-Armor

60 SOVIET AND U.S. TANK DEVELOPMENT

of Tanks (thousands 30

0 Year 1948 1958 1968 1978 1988

* Classified or unknown

U.S./SOVIET T-55 T-62 T-64 T-72 M-1 T-80 FST-I

Crew 4 5.,,,,.,,,,.,,,,,,,,,,,,,,,,,,4 4 4 4 3 3 4 3 ● * Combat Weight 35 41 57 42 (metric ton) Power/Weight Ratio 14.4 17.5 18.0 14.2 184 higher . * (horsepower/rnetric ton) * Maximum Road Speed 48’ 48 42 48 50 50 80 60 66 90 (kilometer/hour) * Main Gun Diameter 100 90 90 105 100 115 125 125 105 125 (millimeter) Turret Front Armor 115 203 242 * 280 , * Thickness (millimeters) 203

Soviet tank development outpaces that of the U.S. both in total numbers and in the introduction of modern technology. The Soviets regard the tank as the primary element of their ground combat power, and Soviet military theory emphaslzes the Importance of the tank in the combined-arms team. As a result, the Soviets commit a major portion of their resources to their tank industry, achieving an Integrated, evolutionary program of tank development that produces thousands of main battle tanks each year. Long-term improvement can be seen In all three Soviet armor subsystems-firepower, protection, and mobility. Modern tanks (T-64, T-72, and 1-60) now make up approximately forty per cent of the Soviet force in the field. (The information for this figure was compiled by the International Technology Division of the Los Alamos National Laboratory.)

Los Alamos Science Summer 1989

Armor/Anti-Armor

Aluminum Company of America (ALCOA), General Motors Delco Systems Operation, A.R.A.P. Division of California Research and Technology

But the situation started to reverse people in the weapons community fear portant. To improve fracture toughness itself in the mid-to-late 1970s when that fielded chemical-energy warheads without sacrificing the other properties, the advent of spaced armor, then ce- are now obsolete. However, prelimi- we are investigating the use of single- ramic laminate armor, and finally re- nary tests of some new chemical-energy crystal whiskers or platelets as a rein- active armor reduced the effectiveness warheads developed by Blue Team con- forcement in ceramics. Tailoring mate- of chemical-energy weapons. Today tractors show promising results. Signifi- rial properties for specific applications is the combination of spaced or ceramic cant improvements in performance seem one of the challenges of armor develop- armor and reactive appliques has prob- attainable with existing technology. Un- ment. ably made every fielded system using a fortunately, we cannot give more details chemical-energy warhead obsolete. on these developments due to the pro- Interface With Industry Reactive armor-used first by the Is- prietary nature of the new designs. raelis in the 1970s and now estimated We can, however, talk about one How is Los Alamos helping industry to be on half of the Soviet tanks—is a promising concept—tandem chemi- to meet the challenges of the Armor/An- formidable challenge (Fig. 2). It was cal-energy warheads (Fig. 3). In these ti-Armor Program’? A recent incident developed primarily as a countermea- weapons a small charge at the front of illustrates how ATAC’s presence at Los sure for chemical-energy weapons and the warhead fires to activate the tank’s Alamos allows the program to tap the consists of a trilayered sandwich of reactive armor. A time delay allows the Laboratory’s experience and developed metal, high explosive, and metal. Tile- reactive-armor plates to move out of the technology. Los Alamos has always like boxes of reactive armor are simply way, then a large shaped charge further performed nondestructive inspections bolted to vulnerable areas of a tank out- back in the warhead fires a metal jet to of every nuclear weapon system tested. side its existing armored shell. defeat the base armor. Weight reduction It was thus only natural to perform the Because of the ability of reactive ar- technologies, various time delays be- same tests on the chemical-energy war- mor to destroy an incoming jet, some tween the firing of the two charges, and heads sent to us by Blue Team contrac- innovative designs and materials for the tors. The evaluations revealed hereto- shaped-charge liners are currently being fore undetected cracks and voids in developed. Blast shields between the some of the warheads that could have precursor and the main charge are being affected performance. We informed optimized, and the most effective stand- the contractors of the problems so they off distance- the distance to the shaped could make substitutions, thus ensuring charge at the instant of its detonation— that all participants had a fair chance in is being determined. Tandem chemical- the competition. energy warheads seem likely to play an ATAC also provides direct help in important role in the defeat of reactive solving contractor’s problems. Our armor. program managers, test directors, hy - The national Armor/Anti-Armor Pro- drocode developers, and materials sci- gram has also taken up the challenges of entists deal on a one-to-one basis with new composite materials and advanced our industrial counterparts. For exam- REACTIVE ARMOR processing techniques. To achieve the ple, last summer we worked with the low weight and elevated mechanical company that produces the Joint Ser- Fig. 2. Reactive armor typically has a layer of properties needed for armors, the ideal vices hypervelocity missile to help solve high explosive sandwiched between two lay- material may actually be a composite a control problem. The missile con- ers of armor plate. When a high-energy jet col- of ceramic and high-strength reinforce- sists of a large kinetic-energy penetra- lides with the armor, the explosive detonates, ments. Ceramics possess low density, tor mounted in the missile’s warhead. pushing the plates into the path of the jet to high hardness, dilatancy (the tendency Although the warhead is very heavy, deflect or deform it, thereby protecting the in- to expand when fractured), and high the missile is long range and able to ner layer of armor. Ideally, the reactive armor shear strength—all good properties for move fast— 1.7 kilometers per second. plate will be moving at an angle to the path of armor-but they lack fracture tough- Unfortunately, the aluminum tins on the jet, forcing it to drill a slot rather than a ness, the ability to resist crack propa- the missile-critical to its stability and hole through the plate and giving the plate a gation, which for some purposes, such control-melted during flight. We even- larger effective thickness. as multiple-hit resistance, may be im- tually solved the problem by suggesting

Los Alamos Science Summer 1989 57 A TANDEM WARHEAD

Fig. 3. One concept for defeating reactive armor is to use a chemical-energy warhead with two explosive charges rather than one. As the warhead approaches the armor (1 through 3) the small explosive charge at the front of the warhead is detonated. The resulting impact activates the explosive in the reactive armor (4 through 6), causing the plates of armor to be blown away. Later, the large explosive charge at the rear of the warhead fires (7). However, the angle of the armor and the gap between the warhead’s initial and final charges causes the plates to miss the penetrating jet formed by the detonation of this second charge. Armor/Anti-Armor

California Research & Technology, Kaman Sciences, Inc., Lawrence Livermore National Laboratory, Radkowski Associates, General Dynamics

both a particular ceramic coating and an ROCKET SLED application technique for the coating. Fig. 4. A chemical-energy warhead is shown being tested on the rocket sled at Los Alamos. ATAC Facilities Mounted on a 1000-foot monorail, the sled can reach Mach-1 speeds and allows scientists to test warheads under controlled but realistic conditions. ATAC, in its role of testing and evaluating the competing antitank systems and armors, uses Laboratory expertise, technologies, and capabilities. For example, we are testing chemical-energy warheads using the 1000-foot monorail rocket sled track at Los Alamos (Fig. 4). The sled can reach Mach-1 speeds, and the track can be extended to 2000 feet if higher speeds become necessary. The sled track is very useful for carrying out realistic tests of tandem-warhead FLASH X-RAY MACHINE designs. Most tandem designs have a significant time delay between firing the Fig. 5. A flash x-ray machine being constructed at Los Alamos capable of “viewing” ballistic first and second warheads, during which events through eight inches of steel. When the 8 to 10 million electron volts of energy stored in time the second warhead moves consid- the Marx generator are released into the diode envelope, electrons accelerated from the cathode erably. The rocket sled can be used to to the anode will generate an x-ray fluence greater than 500 roentgens 1 meter from the end of test the effect of missile motion under precisely controlled conditions. We are also building a new intense flash x-ray machine next to the sled track, This machine should allow armor and anti-armor developers to “see” the penetration process through eight inches of steel (Fig. 5). The source in this system will operate at 8 to 10 mega-electron-volts (MeV) and generate an x-ray dose greater than 500 roentgens at 1 meter. This device will easily track both kinetic-energy Penetrators and chemical-energy jets well inside the logged and processed automatically by ATAC built the range at TERA because targets. computers, which allows Los Alamos sufficient land was not available at Los Los Alamos also designed and helped personnel to control the firing times Alamos for safe firing of full-size live develop a state-of-the-art test range in of munitions and to measure time and miss iles and projectiles. Socorro, New Mexico, at the Terminal space information relative to the arrival A variety of other diagnostic ca- Effects Research and Analysis (TERA) of the devices. Technical calculations pabilities are available for gathering branch of the New Mexico Institute can be done directly from the video. the maximum data from each test per- of Mining and Technology. The range There is also a four-camera. single- formed at Los Alamos, These include occupies 1 square mile and features a image system with a ten-nanosecond four portable 2-MeV x-ray systems, highly instrumented target area that fol- shutter speed. The multiple cameras, twelve 450-keV flash x-ray machines. lows the incoming trajectory and target combined with electronic imaging, per- five rotating-mirror streak cameras with response optically. A continuous record mit Los Alamos personnel to locate the writing speeds of 20 millimeters per mi- of the test is provided by an advanced position of munitions within the target crosecond. four image-intensifier cam- video system that operates at speeds up area and not interfere with the muni- eras with X)-nanosecond shutter times, to 2000 frames per second. All data are tions control and guidance equipment. a laser velocitmeter and a microwave

Los Alamos Science Summer 1989 59 Armor/Anti-Armor

General Electric Company, Ordnance Systems Division, Science & Technology Associates, New Mexico Institute of Mining & Technology

Fig. 6. One of the goals of the national Armor/Anti-Armor program is to establish a useful flow of information between the military, industry, and various research institutions. The interactions of ATAC with this network continue beyond the research phase into the testing, development, and perhaps even production phases of the weapon systems.

Richard Mah is the director of ATAC and a formcr group leader in the Materials Science Division al Los Alamos. Prior to coming to the Laboratory, he worked as a senior research engineer at Dow Chem- ical and C. F. Braun & Co. Hc holds dcgrccs in theoretical and applied mechanics and metallurgical cngineering from the Universiy of Illinois and has published over twenty papers on materials science velocimeter to record transit velocities, Armor-Materials by Design”). When topics. time-interval meters with nanosecond the military told the Laboratory about resolution, 200-megahertz analog-to- the need for a less expensive ceramic digital signal converters, and a wide armor, our materials scientists tested range of more conventional instrumen- various ideas and developed a process tation, We also can use PHERMEX, for fabricating a less expensive but a 30-MeV flash x-ray machine, and equally effective ceramic armor. We ECTOR, a 3-MeV machine. Both of then initiated transfer of the technolog- the machines have access to impressive ical concepts to industry, and Allied digital-enhancement capabilities for flash Signal used the ideas to develop their radiographs, and they allow us to deter- own armor package. Allied Signal is mine the internal structure of anti-armor now busy producing prototypes of the and armor devices at the time of impact armor, which they will submit for test- (see “Studying Ceramic Armor with ing and evaluation at ATAC. If that ar- PHERMEX”), mor is successful in the competition, it will eventually become a new product An Evolving Process available for military use. The true value of the national Armor/ At ATAC we can see a new process Anti-Armor Program may not lie in a Phyllis Martell is the technical writer and public re- evolving among industry. the military, simple leapfrogging of Soviet armor and lations manager for ATAC at Los .Alamos and pub- lishcs a newsletter, The BULLET, on Armor/Anti- and the Laboratory in which a natural bullets by U.S. technology. Rather it Armor Program activities. Before joining the Lab- interplay of needs, research, testing, pro- may lie in the way this uniquely struc- oralory, she was the public information officer for totyping, evaluating, developing, and tured program has opened fresh inter- the Los Alamos School District. She holds a de- procuring guides the development of actions between our nation’s military, gree in French and English from the University of armor and anti-armor systems (Fig. 6). industries, laboratories. and universities Wisconsin. To illustrate how the process works, that will allow us to constantly maintain consider the case of ceramic-filled poly- an edge over the Soviets. ■ mer armor (described in “Armor/Anti-

60 Los Alamos Science Summer 1989 Armor/Anti-Armor

Studying Ceramic Armor with

by Ed Cort

he ballistic impact of penetrator against armor is a brief moment Tof violence and shock hidden in a confusion of smoke and debris (Fig. l,). If we are to learn what material properties are relevant to the outcome, we must pierce the veil and freeze in place the key aspects of this event. Large x- ray machines are ideally suited to this task. A short flash of intense x-radiation Fig. 1, Live fire test of the M1A1 Abrams tank at Aberdeen Proving Ground. (Photograph taken by can penetrate the debris and armor and U.S. Army Combat Systems Teat Activity and provided to Los Alamos by the U.S. Army Ballistic etch an instantaneous image of deforma- Research Laboratory.) tion and material flow. We are currently using an x-ray machine called PHERMEX (Fig. 2) to study the internal structure of ceramic armor during impact with both penetrating jets from chemical-energy weapons and long-rod kinetic-energy penetrators. The machine uses a 30-MeV high- current linear accelerator to generate very intense but short-duration bursts of x rays from a thin tungsten target. Al- though built in the early 1960s, PHER- MEX is still unequaled at producing high-resolution radiographs of large, fast. objects. We are particularly interested in using PHERMEX to study ceramic armor because the mechanisms by which

mors. We have only recently begun to penetrators (fired from the gun at the right).

Los Alamos Science Summer 1989 6 1 Armor/Anti-Armor

,’

,. ,,

undmtand what tiwse differences are. of four to six nominally identical shots The lqqg~f@~ti~a@r pi~mes a W- produces a time-resolved penetration ~et,”~W@@@cor Q~rwiae, by history for one ceramic material and one depoiiiti&hr&~ amounts df kiinetic ,en- ef set of engagement conditions (velocity, e~, in ~:,~~rt~ed region,” The *, obliquity, and yaw) in one plane. In fu- Whicll ~itt’ & $i$@&qj ‘~ a“right Cir” ture tests, we hope to flash PHERMEX

Our current test series ranges over three ceramic materials (boron carbide, aluminum oxide, and titanium diboride), two impact velocities, two obliquities, a number of confinement geometries, and both kinetic-energy rods and jets from chemical-energy weapons. We also look at the flight characteristics of the penetrator (velocity, yaw in two orthogonal planes, rate of change of yaw, and fiducial time at impact). We are modeling the tests with existing hydrocode models (see “Modeiing Armor Penetration”). The code predicts that because the ceramic is relatively in- compressible, even when fractured, and because there is no free volume for the rubble to expand into except the penetration hole itself, the ceramic defeats the penetrator. Although the predic- tions of ‘the model are reasonably close to actual events (Fig. 4), our material model for the ceramic, at the moment, is based more on experimental data from prior tests rather than on principles of physics. Consequently, if the rod’s velocity, say, were to change significantly, we would not be able to extrapolate with confi~ence. At the end of our current series of ttppr@xirnat63y thirty shots, an advi- SO~ panpl ‘{f ex@@~ ‘will review the ~@ts and,itel~ inkttp~t @ data. How- tiv~r, preliminary rkk@s confirm that $%@tsncy (the teni%h$y of the fractured mamic k sxpand) is an important gen- @# femti~ for the c@ft3at of jets fired *W e~@i@*!@ ~e-. ~ this *~~@ *&*~,~*&~fills me itiqxict hole, constantly’fmcing the jet to penetrate new material, and, as the Armor/Anti-Armor

CERAMIC PENETRATION

Fig. 4. (a) A PHERMEX radiograph of a tungsten-alloy penetrator colliding with the eeramlc target of Fig. 3. (b) The same event at the same moment in time es simulated with the HULL hydrocodes. (See “Modeling Armor Pen- etration” for a dlscussion of the hydrocodes.) The iight blue areas in the computer simuia- tion are regions of faiied ceramic that do not appear in the radiograph because of Iack of resolution and the tight conflnement of the ceramic by the target holder.

rubble flows from the impact hole, it pushes inward and attacks the jet from the sides. In the case of long-rod penetrators, material flows out the hole but does not appear to attack the sides of the penetrator as it goes. From these experiments, we should obtain radiographs of the dilatancy mechanism in action and accurate materials data on such things as the hardness of the ceramic, One of the main points of the tests is to accumulate more accurate experimental data to validate code-modeling parameters for armor and anti-armor designers. Although the PHERMEX experiments provide valuable data, several funda- mental questions about the dynamic behavior of ceramic armor are more easily addressed in laboratory experiments. One question concerns the sequence of events-does fracture occur at the rear of the ceramic (Fig. 4) during the pas- sage of the initial shock wave or later as the penetrator forces its way through the material? In addition, scientists must determine what factors dictate the size and shape of the individual fractured particles and then understand how to model penetration of the resulting pul- verized material. To address such questions, Los Ala- mos scientists have designed two experiments that complement the PHERMEX

Los Alamos Science Summer 1989 Armor/Anti-Armor

The role of penetrator velocity, plate spacing in multilayered armor, and yaw (the angle of the penetrator’s axis with respect to its velocity vector) can be as- sessed easily, and armor designers can test their understanding and arrive at new insights by changing and optimiz- ing such parameters. The results of a computation. done before the experiment Modeling can be used to guide test design by an- swering questions about the most advan- tageous locations for the instruments, the proper scale ranges for recording data, and the important experimental variables. The goals of the computational research being carried out under ATAC’s by Ed Cort direction are to validate and benchmark codes and methods, to pinpoint areas of needed research, and to improve existing codes-especially the ability to deal rmor and anti-armor technology with a three-dimensional modeling of is becoming increasingly com- impact and penetration. A The hydrocodes used in the simu- ers to rely more and more on computer lations are grounded in classical con- modeling. For years, computer simula- tinuum mechanics, which attempts to tions of armor penetration contributed describe the dynamics with a set of dif- only modestly to armor development ferential equations bed on the con- compared, say, to the role of computa- servation of mass, momentum, and en- tional fluid dynamics in the aircraft and ergy. An equation of state relates the aerospace industries. However, com- material’s density, internal energy, and puter modeling is becoming a major tool pressure. Finally, a constitutive equation in the study of armor-penetrator inter- describes the stress-strain relationship actions by offering weapons designers in the material,,, , and reflects changes in a number of distinct advantages in their the properties of the material, such as quest of an essential understanding of work hardening that result from severe the processes. distortion. In fact,,, there is a frequent For example, the destruction and the need to model the material after it has speed of ballistic penetration make ex- failed, a need that may sometimes dis- perimental diagnostics expensive, dif- tort the usual assumptions of continuum ficult to interpret, and, in many cases, mechanics beyond simple extrapolation. impossible to gather. In comparison, From a practical point of view, the a computer simulation, when bench- ideal design code should have a user in- marked against even limited test data, terface that allows problems to be set can “replay” the experiment in slow up conveniently, standardized material motion. Computer modeling can also models and properties that can be ex- resolve velocity and stress and strain panded or modified easily, and powerful components in the target and penetrator graphics and post-processing that can in fine detail and pinpoint the relative depict results quickly and in a man- interaction between armor components. ner that is easy to interpret. The code

54 Armor/Anti-Armor

should be accurate in the physics and tration of spaced armor, which has mul- targets-up to 10 times as thick as the material behavior it intends to model tiple layers of armor separated by gaps preliminary example—would require as well as in the numerical implemen- and set at oblique angles to the penetra- considerably more computer time to tation and programming that translate tor’s line of flight. The intent of such model. Our evaluation was that HULL equations into code. The code must a configuration is for the obliquity of is a useful but limited code. be adaptable to a wide variety of prob- the plates to deflect, bend, or break the The evaluation, coupled with many lems, efficient in memory use and run- long rod so that later plates can stop the other code comparisons, motivated us to ning time (although, here, the defini- residual pieces more easily. Reactive develop a new three-dimensional code tion of what is unacceptable constantly armor is another type of multilayered ar- designed specifically for simulations changes), and robust enough that the mor that also attempts to interfere with of armor and anti-armor systems. The code does not fail when it encounters an the rod’s trajectory. In this case yaw is code, called MESA, is Eulerian and unexpected situation. created on impact when a layer of ex- treats hydrodynamic flow and the dy- The bulk of the computer codes used plosive ignites, shoving a plate of armor namic deformation of solid materials. on a production basis fall into two cat- toward the penetrator to knock it askew. Because it uses state-of-the-art numer- egories: Eulerian and Lagrangian. Sim- A computer simulation of the pene- ical methods, it runs faster and is less ply stated, Eulerian methods move the tration of spaced armor plate will be re- affected by spurious numerical problems material through a fixed mesh as the alistic only if the code deals accurately than existing Eulerian codes. The ver- problem progresses whereas Lagrangian with (1) the erosion of the front of the sion of MESA now being tested incor- methods have a computational grid at- rod as it penetrates a plate, (2) the loss porates several of the standard strength tached to the material that distorts with in velocity of the residual rod, (3) any models that take into account both the movement of the material. (Eulerian changes in the orientation of the rod, elastic and the plastic regions of the codes are frequently used in fluid dy- and (4) the yielding and failure in the stress-strain relationship of the materi- namics whereas Lagrangian methods are plate. We tested the ability of HULL to als. There is also a programmed-bum more often used in structural analysis,) model armor penetration accurately by model for the explosives. We have Each method has its peculiar advantages having it simulate a set of experiments developed ‘a number of such models, and disadvantages. For instance, La- carried out in the late 1970s using the which should increase our ability to grangian methods tend to be faster, can PHERMEX machine. In these experi- simulate a variety of interactions for implement sophisticated material mod- ments, long-rod uranium-alloy Penetra- modern armor systems. In future ver- els more easily, are efficient with large tors impacted steel-alloy plates set at sions of MESA we will include more problems, and treat material interfaces various angles to the flight of the rod. advanced materials models. accurately. However, they also deal in- Comparison of a PHERMEX radiograph One such model, called the Mechan- accurately with large shear flows, are and the corresponding computer simu- ical Threshold Stress model, will incor- more complex to set up, and are not ro- lation (Figure) illustrates how well the porate the physical deformation mech- bust with large distortions such as those code predicted the interaction between anisms needed to simulate conditions that occur when armor penetration is penetrator and target. not easily achieved in the laboratory significant. Eulerian methods are almost These benchmark experiments gave but important to this type of research. a mirror image of Lagrangian methods us confidence that the code had the Specifically, the model will allow us to since they are robust, easy to set up, potential to provide useful informa- extrapolate better into regimes of high and capable of handling large shears and tion about similar experiments with deformation rate, high temperature, and distortions. On the other hand, Eule- more complex targets, such as ceramics, large amounts of strain. The model sep- rian codes tend to be less accurate in the whose interaction with the penetrator arates the kinetics of strain hardening treatment of material interfaces, ineffi- was more difficult to model, But a com- (that is, dependencies on temperature cient in the use of computer memory, putation of this type pushed HULL to and strain rate) from the kinetics related difficult to implement with more sophis- the limit of its capability—it had a run- to the strength at a given instant. So far ticated material models, and generally ning time in a CRAY X-MP computer we have demonstrated the model only slower in running. of 11 hours, and the computer mem- for certain well-characterized metal- In our work at Los Alamos, we first ory would not hold enough information lic systems, but we are extending it to explored an existing three-dimensional to model a second target plate with an the more complicated materials used Eulerian code, HULL. We wanted to intervening space. Even if larger com- in armor and anti-armor applications. test its ability to accurately predict pene- puter memories were available, realistic We also hope to combine the defor-

Armor/Anti-Armor

Table Current application of MESA (funded by the Department of Defense and the Army Missile Command as well as DARPA, the Defense Advanced Research Project Agency).

Los Alamos Science Summer 1989 67 !

This report was prepared as an account of work sponsored by the United States Government. Nei- ther the United States Government, nor the United States Department of Energy, nor any of their em- ployees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific com- merical product, process, or service by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Gover- nment or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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