Editing Kinetic energy penetrator

{{Short description|High density non-explosive projectile}}{{More citations needed|date=October 2007}}
[[File:Obus-flèche français OFL 120 F1.jpg|thumb|French anti-tank round with its sabot]]

A '''kinetic energy penetrator''' ('''KEP'''), also known as '''long-rod penetrator''' ('''LRP'''), is a type of [[ammunition]] designed to [[penetration (weaponry)|penetrate]] [[vehicle armour]] using a [[flechette]]-like, high-[[sectional density]] [[projectile]]. Like a [[bullet]] or [[kinetic energy weapon]], this type of ammunition does not contain [[explosive]] payloads and uses purely [[kinetic energy]] to penetrate the target. Modern KEP munitions are typically of the [[armour-piercing fin-stabilized discarding sabot]] (APFSDS) type.

==History==
[[File:APFSDS-T-01.jpg|thumb|upright=0.6|A partly cut-away 30 × 173&nbsp;mm [[Armour-piercing fin-stabilized discarding sabot|APFSDS]]-[[Tracer ammunition|T]] round]]
Early cannons fired kinetic energy ammunition, initially consisting of [[round shot|heavy ball]]s of worked [[stone]] and later of [[heavy metals|dense metals]]. From the beginning, combining high [[muzzle energy]] with projectile weight and [[hardness]] have been the foremost factors in the design of such weapons. Similarly, the foremost purpose of such weapons has generally been to defeat protective [[shell (structure)|shell]]s of [[armored vehicle]]s or other [[fortification|defensive structure]]s, whether it is stone [[defensive wall|wall]]s, [[sailship]] timbers, or modern tank armour. Kinetic energy ammunition, in its various forms, has consistently been the choice for those weapons due to the highly focused [[terminal ballistics]].

The development of the modern KE penetrator combines two aspects of artillery design, high [[muzzle velocity]] and concentrated force. High muzzle velocity is achieved by using a projectile with a low mass and large base area in the gun barrel. Firing a small-diameter projectile wrapped in a lightweight outer shell, called a [[sabot (firearms)|sabot]], raises the muzzle velocity. Once the shell clears the barrel, the sabot is no longer needed and falls off in pieces. This leaves the projectile traveling at high velocity with a smaller cross-sectional area and reduced aerodynamic drag during the flight to the target (see [[external ballistics]] and [[terminal ballistics]]). Germany developed modern sabots under the name "''treibspiegel''" ("thrust mirror") to give extra altitude to its [[anti-aircraft warfare|anti-aircraft guns]] during the [[World War II|Second World War]]. Before this, primitive wooden sabots had been used for centuries in the form of a wooden plug attached to or breech loaded before cannonballs in the barrel, placed between the propellant charge and the projectile. The name "sabot" (pronounced {{IPAc-en|ˈ|s|æ|b|oʊ}} {{respell|SAB|oh}} in English usage)<ref>''Shorter Oxford English Dictionary'' (2007) 6th Ed. p. 2641</ref> is the French word for [[clog (shoe)|clog]] (a wooden shoe traditionally worn in some European countries).

Concentration of force into a smaller area was initially attained by replacing the single metal (usually [[steel]]) shot with a composite shot using two metals, a heavy core (based on [[tungsten]]) inside a lighter metal outer shell. These designs were known as [[Armour-piercing ammunition|armour-piercing composite rigid]] (APCR) by the British, high-velocity armor-piercing (HVAP) by the US, and ''hartkern'' (hard core) by the Germans. On impact, the core had a much more concentrated effect than plain metal shot of the same weight and size. The air resistance and other effects were the same as for the shell of identical size. High-velocity armor-piercing (HVAP) rounds were primarily used by [[tank destroyer]]s in the [[United States Army|US Army]] and were relatively uncommon as the tungsten core was expensive and prioritized for other applications.

Between 1941 and 1943, the British combined the two techniques in the [[armour-piercing discarding sabot]] (APDS) round. The sabot replaced the outer metal shell of the APCR. While in the gun, the shot had a large base area to get maximum acceleration from the propelling charge but once outside, the sabot fell away to reveal a heavy shot with a small cross-sectional area. APDS rounds served as the primary kinetic energy weapon of most tanks during the early-Cold War period, though they suffered the primary drawback of inaccuracy. This was resolved with the introduction of the [[armour-piercing fin-stabilized discarding sabot]] (APFSDS) round during the 1970s, which added stabilising fins to the penetrator, greatly increasing accuracy.<ref>{{Cite web|url=https://www.britannica.com/technology/tank-military-vehicle|title=Tank - Armament|website=Encyclopedia Britannica|language=en|access-date=2020-02-22}}</ref>

==Design==
The principle of the kinetic energy penetrator is that it uses its kinetic energy, which is a function of its [[mass]] and velocity, to force its way through armor. If the armor is defeated, the heat and [[spall#Antitank warfare|spalling]] (particle spray) generated by the penetrator going through the armor, and the pressure wave that develops, ideally destroys the target.<ref>{{cite web |url=http://xbradtc.wordpress.com/2008/07/07/heat-rounds-and-sabots |title=Heat Rounds and Sabots |url-status=dead |website=xbradtc.wordpress.com |archive-url=https://web.archive.org/web/20110718112901/http://xbradtc.wordpress.com/2008/07/07/heat-rounds-and-sabots/ |archive-date=2011-07-18}}</ref>

The modern kinetic energy weapon maximizes the [[Stress (mechanics)|stress]] (kinetic energy divided by impact area) delivered to the target by:
* maximizing the mass – that is, using the [[density|densest]] metals practical, which is one of the reasons [[depleted uranium]] or [[tungsten carbide]] is often used – and [[muzzle velocity]] of the projectile, as kinetic energy scales with the mass ''m'' and the square of the velocity ''v'' of the projectile <math>(mv^2/2).</math>
* minimizing the width, since if the projectile does not tumble, it will hit the target face first. As most modern projectiles have circular cross-sectional areas, their impact area will scale with the square of the radius ''r'' (the impact area being <math>\pi r^2</math>). For the same reason, "self-sharpening" through the generation of [[adiabatic shear band]]s is also a desired feature for the projectile material.<ref>{{Cite journal |last=Magness |first=Lee S. |date=1994-03-01 |title=High strain rate deformation behaviors of kinetic energy penetrator materials during ballistic impact |url=https://linkinghub.elsevier.com/retrieve/pii/0167663694900558 |journal=Mechanics of Materials |language=en |volume=17 |issue=2-3 |pages=147–154 |doi=10.1016/0167-6636(94)90055-8}}</ref>

The penetrator length plays a large role in determining the ultimate depth of penetration. Generally, a penetrator is incapable of penetrating deeper than its own length, as the sheer stress of impact and perforation ablates it.<ref>{{Citation|title=M829A3 penetration test|url=https://www.youtube.com/watch?v=EodS_Ss8a5I |archive-url=https://ghostarchive.org/varchive/youtube/20211211/EodS_Ss8a5I |archive-date=2021-12-11 |url-status=live|language=en|access-date=2020-02-22}}{{cbignore}}</ref> This has led to the current designs which resemble a long metal [[arrow]].

For monobloc penetrators made of a single material, a perforation formula devised by Wili Odermatt and W. Lanz can calculate the penetration depth of an APFSDS round.<ref>{{Cite web|title=Long Rod Penetrators. Perforation Equation |url=http://www.longrods.ch/perfeq.php|website=www.longrods.ch|access-date=2020-02-22}}</ref>

In 1982, an analytical investigation drawing from concepts of gas dynamics and experiments on target penetration<ref>{{cite journal |last1=Bondarchuk |first1=V.S. |last2=Vedernikov |first2=Y. |last3=Dulov |first3=V.G. |last4=Minin |author4-link=Vladilen F. Minin |first4=V.F. |title=Optimization of star-shaped penetrators |journal=LZV. Sib. Otd. Akad. Nauk SSSR Ser. Tekh. Nauk |language=ru |volume=13 |pages=60–64 |date=1982}}</ref>{{coi-source|sure=yes|date=July 2020}} led to the conclusion on the efficiency of impactors that [[Impact depth|penetration]] is deeper<ref>{{cite journal |last1=Bivin |first1=Y.K. |last2=Simonov |first2=I.V. |title=Mechanics of Dynamic Penetration into Soil Medium |journal=Mechanics of Solids |publisher=Allerton Press |volume=45 |pages=892–920 |date=2010 |issue=6 |issn=0025-6544 |doi=10.3103/S0025654410060130 |bibcode=2010MeSol..45..892B |s2cid=120416067}}</ref> using unconventional three-dimensional shapes.<ref>{{cite journal |last1=Ben-Dor |first1=G. |last2=Dubinsky |first2=A. |last3=Elperin |first3=T. |title=Area rules for penetrating bodies |journal=Applied Fracture Mechanics |publisher=Elsevier Ltd. |volume=26 |pages=193–198 |date=1997 |issue=3 |issn=0167-8442 |doi=10.1016/S0167-8442(96)00049-3}}</ref>

==See also==
{{Div col}}
* [[Compact Kinetic Energy Missile]]
* [[Earthquake bomb]]
* [[Flechette]]
* [[Hellfire R9X]]
* [[Impact depth]]
* [[Kinetic bombardment]]
* [[MGM-166 LOSAT]]
* [[Röchling shell]]
{{Div col end}}

==Notes==
{{Reflist}}

==References==
{{Refbegin}}
* {{cite journal |last1=Cai |first1=W. D. |last2=Li |first2=Y. |last3=Dowding |first3=R. J. |last4=Mohamed |first4=F. A. |last5=Lavernia |first5=E. J. |year=1995 |title=A review of tungsten-based alloys as kinetic energy penetrator materials |journal=Review of Particulate Materials |volume=3 |pages=71–131}}
{{Refend}}

[[Category:Anti-tank rounds]]
[[Category:Projectiles]]
[[Category:Ammunition]]
[[Category:Collision]]
[[Category:Tank ammunition]]