Armor Technology: Part III

rial.% Soviet ballisticians have referred to these analyses as being based on the “hypothesis of flat sections,” wherein each theoretical layer of material is pushed exactly to the side of the penetrator in order to form the crater.59 The methods have even been applied to the penetration of soils and rocks, as well as underground explosions.59 The Soviet ballistician,

A. Ya. Sagomonyan, has also noted specifically the effeds of penetrator nose shape on deformation and that the hypothesized thin layers could actually be layers of different material such as used in a laminate The importance of the ductility ofthe last structural layer of a composite or laminate array (or the back of a solid armor) cannot be understated, as it must maintain the structural integrity of the armor and ehicle.2~. 26 This layer must of necessity be capable of resisting penetration, if the penetrator reaches it, as well as capable of absorbing the kinetic energy (momentum) of the impact into the armor or array.l0, 26* 61, 62 However, this will more likely than not be overmatched at some point during the life of the armored vehicle. It is most important then that this final structural layer not contribute to the behind-armor debris or “spall” at this time, as well as remain structurally sound. If an armor array is overmatched by a charge or projectile that batters it or pierces it, then it becomes important to protect the occupants of the vehicle from the behind-armor debris. An ancient way of accomplishing this was to hang curtains behind and away from the wall of fortifications.63.64 The effectiveness of such shields can be as great as that described by Lt. A. D. Whartan of the Confederate ship Tennessee after having been hit by a 15-in. shot from the Union monitor Manhattan? “The Monogahela was hardly clear of us when a hideous looking monster came creeping up on our port side, whose slowly revolvingturret revealed the cavern-ous depths of a mammoth gun. ‘Stand clear of the port side,’ I shouted (and), a moment after, a thunderous report shook us all, while a blast of dense, sulphurous smoke covered our portholes, and 400-pounds of iron, impelled by 60 pounds of powder, admitted daylight through our sides, where, before it struck us, there had been over 2 feet of solid woad, covered with 5 inches of solid iron. This was the only 15-inch shot that hit us fair. It did not come through; the inside netting caught the splinters, and there were no casualties from it.” Thus, although the armor array was severely perforated, the netting (spall curtains) caught the behind-armor debris that could have caused serious injury to the crew. Recent research by the US Army Materials and Mechanics Research Center has proved the value of similar liners of modern materials, such as Kevlar, in armored personnel carriers.65 Thus, they are greatly recommended, and have previously been noted to have been used in Soviet vehicles such as the T-55 and T-72 main battle tanks. A similar service of protection from bolts and armor splinters was performed by 9-mm ducol steel plates that were installed 700-mm underneath the armored decks of the Japanese battleship Yumato.66 Needless to say, spall curtains can be overmatched just like an armor array. Still, they might canalize the penetrator and debris to protect the crew of an armored vehicle.

The “fairness” of a projectile hit has historically been associated with striking an armor square-on as it has long been recognized that an oblique impact is not as efficient in penetrating armor. However, the use of armor obliquity to defeat kinetic-energy penetrators also brings out some differences in armor design philosophy between various countries. For example, the degree of perforation, whether complete or partial, wherein the penetrator broke through the armor but did not itself exit, is a small point of variance beside the overall methods of evaluation which can be explained by the following.29. 53 Ballistic limit velocity (U.S.) attempts to find that velocity at which 50 percent of the projectiles striking the specific array will be defeated.

Critical velocity (U.K.) attempts to define the velocity at which perforation with negligible residual penetrator velocity occurs.

Critical angle (Germany, U.S.S.R.) attempts to find the obliquity angle at which the armor material will defeat the penetrator at a specific impact velocity. The U.S. and U.K. methods attempt to relate the range-related impact velocity at which the armor array defeats the penetrator or the penetrator defeats the armor array. In other words, it is concerned with how close a vehicle’s armor array can be brought to an enemy’s gun before holes get poked through it. Conversely, the method tells how far away a specific gun and kinetic-energy penetrator can be fired at an enemy and still poke holes through the enemy’s armor array. This was of major concern for the conduct of naval battles on the open seas.

The critical angle method is concerned with the use of armor obliquity to protect against a specific fielded threat that might be encountered at a specific range at the lowest armor weight. Any additional “compound” obliquity obtained by engagement at an angle from the sides of the obliquity rotation plan can be considered by the armored vehicle designer to provide additional protection. This method of armor evaluation is most applicable to weight-efficient protection from point-blank attacks, such as those that occur when APFSDS (sabot) ammunition is used by tanks. It should be noted, however, that shaped charges always present a point-blank attack, as the penetrating jet is formed at the target when the warhead detonates. As previously noted in ARMOR, the metal jet from a shaped charge warhead generally exerts a high enough pressure that its penetration can be described by a fluid dynamic analysis to yield the following equation for “hydrodynamic” penetration: P = L pj/pt where P and L are the depth of penetration and jet length, respectively, expressed in the same units of measure (mm), and pj and pt are the density of the jet and target, respectively, expressed in the same units (grams/cc).32 The penetration is also little affected by the obliquity of the impact unless the geometry causes the warhead sides to be close to the armor or some other materiel.32 In this case, the result is an imperfectly formed jet rather than material resistance to penetration.

The effect of target hardness of shaped-charge jet penetration has been analyzed by a number of researchers to the formulation of the following principal observation:^^ Increased target hardness decreases the rate of penetration by the jet, until At a specific “cutoff velocity the pressure exerted by the jet is no longer sufficient to continue penetration. Since the shaped charge jet penetrates in a manner similar to that hypothesized for kinetic energy penetrators as just pushing the armor material to the sides, then its penetration through an elastically-plastically deforming laminate target can be analyzed by means of looking at the behavior of each layer sequentially.12* @ Under the assumptions of the hydrodynamic equation, lower density armor materials should provide less penetration resistance (protection) resulting in deeper craters. Thus, one would anticipate penetrations into aluminum and plastic armors to be about 1.7 and 2.5 times deeper than into steel armors, respectively. However, even if this were the case, it should be noted that the weight of an armor goes up with the cube of its dimensions. Thus, if the protected area remains the same, and only the depth of penetration increases, then the lower density material can still provide a significant weight savings over steel armor. Some additional advantages might also be obtained by the stiffness of the bulk material if it is easily welded into hull forms such as has been found with the use of aluminum for the construction of armored personnel carriers.69, 70 .

70 The British and Soviets acknowledged the effectiveness of high hardness armor materials in resisting shaped charge jet penetration during the 1 9 5 0 ~ . ~ ~ The early data showed the effect of various hardness steels and aluminums. Later, Dr. Trinks provided data on the significant weight savings of Footnotes (continued from Parts I & 11) “G. S. Pearson, “Whither Ballistics,” in Proceedings of the Sixth International Symposium on Ballistics, Orlando, Florida, October 27-29, 1981, American Defense Preparednesa Assoc., Washington, D.C. pp 5-14. 55M. Van Thiel and L. Edwards, “Target Response To High Velocity Penetration,” ibid, pp 346-353.

56W. J. Bruchey, et al., “Performance of Conventional and High-technology Materials as Long-rod Penetrators,” ibid, pp 379-387. 57P. I. Ulyakov, “Anal ic Derivation of the Depth to Which a Fast Thin Rod Penetrates into a Hagspace,” Zhurnal Tekh. Fiz. 51, January 1981, pp 157-163.

58J. E. Backofen, Jr., “ArmorIArmor Penetration: Land, Sea, Air, and Space,” in Proceedings of the Fifih International Symposium on Ballistics, 16-18 April, 1980, Toulouse, France. 59A. Ya. Sagomonyan, Penetration of Solids into Compressed Continuous Media, Moscow University, Moscow, 1974. 6oA. Ya. Sogomonyan, “The Pierci of a Plate by a Thin Solid Projectile,” Vestnik Moskovskogo Universiteta%athematika, Mekhanika, Vol. 30, No.

5. September-October 1975, pp 104-111. GIG. Honica and H. Steinhilber, “Energy Transfer by Projectile Impact of Armor,” Proceedings of the Sixth International Symposium on Ballistics, 27-29 October 1981, Orlando, Florida, pp 363-368. 62Yu. N. Lokhov, et al., “Dynamic Bending of a Plate in Impulsive Mechanical Loading,” Problemy Prochnosti, No. 3, March 1981 pp 32-37.

631. V. Hogg, Fortress:A History ofMilitary Defense, St. Martin’s Press, Inc., New York, 1977. aT. N. Du uy, The Evolution of Weapons and Warfare, The Bobbs-Memll Company, pnc., New York, 1980.

65“Ballistic Liners Improve M113 Survivability Rate,” Army Research, Development, and Acquisition, July-August 1980, p 7. S K . Matsumoto and M. Chihaya, “Design and Construction of the Yamato and Musashi,” US.

Naval Institute Proceedings, October 1953, pp 1103-1113.

67J. E. Backofen,et al.,TheRateof TargetPenetmtion byShapedChargesat Short Standof, Battelle, Columbus Laboratories, Columbus, Ohio, 1981 (available from Defense Technical Information Center, ADB057 447). 19 40 percent for high hardness steels and 65 percent for aluminum oxide aluminum steel laminatess?2 These results, and other claims, have led to controversy for over a decade over the arrangement and performance of laminated composite (compound or combined) armors for use as protection from shaped charges?-7- 72-79 One writer was led to explain that British tank designers had developed the material that became known as Chobham armor in the late 1960’s and released the information of its development in June 1976.73 One may now suspect in 1982 that the release of information on the advanced armor material that would protect tanks from all known shaped charges might have been to prove that the death of the tank in the face of antitank guided missiles might have been prematurely announced after the October 1973 War. The effectiveness of spaced and laminated armors for the defeat of shaped charges had already been presented in popular publications.7l. 82, Similarly, spaced and laminated plastic-filled armors had been developed for protection from shaped charges before and during WW II.32, 51, 84 Still, the recent vogue is to continue the controversies over the effectiveness of and intent to use various laminate armors containing high - hardness materials and/or plastics in the popular press?9~71-82,85-87 And, this occurs while existing tanks, such as the Leopard Z and Centurion, have been uparmored with plastic-backed steel plates forming arrays similar to the laminated arrays being discussed.saW The compressibility of lower density materials, such as plastics and liquids, when subjected to supersonic penetration by shaped-charge jets has been suggested as a possible reason for their high resistance to such penetration.12. 91 However, experimental evidence disagrees with the theoretical research and implies that many low-density materials resist penetration by shaped-charge jets more effectively than the hydrodynamic formula and material compressibility would suggest?2 This means that effective materials such as water and diesel fuel might find very useful positions within tank compound armor arrays7,36*93 in the same way food, water, supplies, and fuel were used in naval vessels well before WW II.S.48*49,6s Thus, the importance of materials to resist shaped charges in the future may depend more on how they are integrated into the overall design of an armored vehicle than they have in past and in a way similar to the naval usage of structure, armor, and materiel to protect against damage by kinetic-energy penetrators. The importance of utilizing all the armored vehicle’s structure and material as protection has recently been recognized by some tank designers.%* 94 They realize that all materials of a weapons platform must offer ballistic resistance to the threats of shock loading and penetration. Armor materials technology must be used to construct the hardest, toughest, fabricable, cost-effective material for the combined roles of structural applications and armor-like resistance capability. Deliberate armor protection by means of mass, high-cost, specifically tailored armor material properties, etc. should further be reserved for application around critical components of the armored vehicle (i.e., men, communication equipment, life support systems, etc.). The latter is an application in the form and requirement of armor materials of the military principal of mass (concentration) at a key objective in battle (subsystedsystem survival). This article has continued the examination of vehicle armor by reviewing the technologies behind the development of armor materials. The discussion will conclude with a review of thepast usage ofarmor materials in armored vehicle arrays and a projection of how they might be used in the future. BJ. N. Majerus, “A Model for Studying the Influence of Guidance Packages Upon Shaped Charge Warhead Performance,” Proceedings of the Second Internationnl Symposium on Ballistics, Daytona Beach, Florida, March 9-1 1, 1976, American Defense Preparedness Assoc., Washington, D.C. ‘39G. W. Budd, editor, The Military Uses ofAluminum. 1973 edition, Alcan Booth Sheet Ltd., Birmingham, England. 7oD. Crow and R. J. Icks, Encyclopedia of Tanks, Chartwell Books, Inc., Secaucus, New Jersey, 1975.

71J.E. Backofen, Jr., “The Weaponization of Shaped Charge T,echnology,” Proceedings of the Fourth International Symposium on Ballcstzcs, October 17-19, 1978, Monterey, Calif., American Defense Preparedness Assoc., Washington, D.C.

72W. Trinks, W. Geiger and H. Kollmannsperger, “Grenzen der Schutzwir-kung von Panzerwerkstoffen gegen Hohlladungen,” Jahrbuch der Wehrtechnik, Folge 6, Wehr und Wissen Verlagsgesellschaft MBH, Darmstadt, 1971, pp 46-50

733. OBallance. “Military Allies But Commercial Rivals,” Armies & Weapons, No. 48, November 1978, pp 6-7. 74J. L. Sorin, “Les Nouveaux Materiaux de Blindage,” Revue de Defense Nationale, Vol. 25, December 1969.

75R. J. Icks, “More Bang for Fewer Bucks,” ARMOR, No. 2, March-April 1976, pp 35-39.

76R. M. Ogorkiewin, “Composite Armour,” Composites, April 1976, pp 71-72.

77R. M. Ogorkiewicz, “Latest Trends in Tank Technology,” ARMOR. May-June 1976, pp 39-44.

78V. Kovalev, “Problems of Tank Protection,” Tekhnika i Vooruzheniye, No. 1, 1977, pp 14-17. “”‘Wohin tendiert die Entwicklung im Panzerbau?,” Militartechnik, No. 4, 1979, pp 207-209.

SOK. Schnell, “E uipment of the West Cerman Armed Forces in the 1980’s and Early Ws,”%ehrtechnik, No. 7, 1979, pp 15-2.6. alB. Fritz, “The AC300 Jupiter, Luchaire’s New Antitank Weapon,”International Defense Reuiew, No. 1, 1982, pp 71-74. 82W. Trinks, “Sha d Char es and Armor: Their Alternate, Continous Development,” Jahrgch der fVehrtechnik, Folge 8, Wehr und Wissen Verlagsgesellschaft, MBh, KoblenziBonn, 1973, pp 154-163. 83R. M. Ogcrkiewicz, Design and Development ofFighting Vehicles, Doubleday & Company, Inc., Garden City, New York, 1968. MR. P. Hunnicutt, Sherman: a History of the American Medium Tank, Taurus Enterprises, Belmont, Calif., 1978. 8WHearing on the Enforcer Aircraft before the Research and Development Subcommittee of the Committee on Armed Services, House of Representatives, Ninety-Fifth Congress, Second Session,’’ June 22,1978, U.S. Government Printing Office, Washington, D.C., 1978. 86E. C. Ezell, “Japanese 1980 Defense Budget and Future R&D Programs,” International Defense Review, Vol. 13, No. 3, 1980, pp 340-344. 87W. Bischofberger, “Panzerwaffen: Feuerkraft und Panzerung in Ver-gleich,” Allgemeine Schweizerische Militaneitschriff, Nr. 12, December 1980, pp 693-698.

88Advertisements by Clouth Gummiwerke AG, such as in Military Technology.Vo1. V, Issue 21, February 1981, p 9. 89Le0pard 1Al m.Z., ARMOR, November-December 1979, pp 27-29, reprinted from Armies & Weapons, No. 47, October 1978, pp 27-29. W“Additiona1 Armour for the Israeli Centurions,” Armies & Weapons, No. 56, July (August) 1979, p 30.

91B. S. Haugstad and 0.

S. Dullum, “Finite Compressibility in Shaped Charge Jet and Long Rod Penetration-the Effect of Shocks,” Journal of Applied Physics, 52 (8). 1980, pp 559.

925. J. White, III and M. J. Wahll, “Shaped Charge Jet Interactions With Liquids,” in Procedings of the Sixth International Symposium on Ballistics, October 27-29, 1981, Orlando, Florida, pp 305-311. 93“NKPZ-the Swiss Tank for the Ws?,” International Defense Review, Special Series 11, pp 5-6. %G. Turbe, “A Situation Report on the Franco-German MBT Project,” International Defense Reuiew, Vol. 14, No. 1, 1981, pp 23-26. JOSEPH E. BACKOFEN. JR.

was commissioned in the Corps of Engineers upon graduation from the Polytechnic Institute of Brooklyn in 1966. While with the 62d Engineer Battalion, his service included Rome Plow Land Clearing Operations in Cambodia and Vietnam. Mr. Backofen is currently involved with the development of advanced weapons technology at Battelle Columbus Laboratories.