Strictly speaking, penetration occurs when a projectile enters a target without passing through it and perforation occurs when the projectile completely passes through the target, but the word penetration is commonly used to refer to either.
Penetration into a semi-infinite or massive target is penetration (in the strict sense of the word) of targets so thick that the level of penetration is not affected by the target's thickness. There is a transition region between semi-infinite penetration and perforation, in which the target is not perforated but the projectile, as it nears the back face of the target, meets reduced resistance and is capable of penetrating a greater distance than it would in a semi-infinite target. This effect is variously named the back or rear surface, plate, or face effect and is also present when perforation occurs.
A penetrating projectile may cause the target to break into multiple pieces, spewing from both the front and back of the target, themselves at high velocity. These pieces are collectively referred to as spall. Spall can be generated even if a perforation is not achieved (the projectile fails to pass through the target), generated instead by the shock wave generated by the impact of the projectile.
Bombs designed for great penetration into the earth or for perforation of hardened targets are known as bunker busters.
Overpenetration
Overpenetration of a projectile through a synthetic ordnance gelatin.
Excessive penetration or overpenetration occurs when a projectile completely passes through (perforates) its intended target and out of the other side, with enough residual kinetic energy to continue flying as a stray projectile, and risk causing unintended collateral damages to objects or persons beyond. According to the energy transfer hypothesis, this happens because the projectile has not released all its energy within the target.
A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Different types of shaped charges are used for various purposes such as cutting and forming metal, initiating nuclear weapons, penetrating armor, or perforating wells in the oil and gas industry.
A kinetic energy penetrator is a type of ammunition designed to penetrate vehicle armour using a flechette-like, high-sectional density projectile. Like a bullet, 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.
A nuclear bunker buster, also known as an earth-penetrating weapon (EPW), is the nuclear equivalent of the conventional bunker buster. The non-nuclear component of the weapon is designed to penetrate soil, rock, or concrete to deliver a nuclear warhead to an underground target. These weapons would be used to destroy hardened, underground military bunkers or other below-ground facilities. An underground explosion releases a larger fraction of its energy into the ground, compared to a surface burst or air burst explosion at or above the surface, and so can destroy an underground target using a lower explosive yield. This in turn could lead to a reduced amount of radioactive fallout. However, it is unlikely that the explosion would be completely contained underground. As a result, significant amounts of rock and soil would be rendered radioactive and lofted as dust or vapor into the atmosphere, generating significant fallout.
Armor-piercing ammunition is a type of projectile designed to penetrate either body armor or vehicle armor.
Terminal ballistics is a sub-field of ballistics and refers to the behavior and effects of a projectile when it hits and transfers its energy to a target.
Chobham armour is the informal name of a composite armour developed in the 1960s at the British tank research centre on Chobham Common, Surrey. The name has since become the common generic term for composite ceramic vehicle armour. Other names informally given to Chobham armour include "Burlington" and "Dorchester." "Special armour" is a broader informal term referring to any armour arrangement comprising "sandwich" reactive plates, including Chobham armour.
High-explosive squash head(HESH), or less commonly known as high-explosive plastic(HEP) is a type of explosive projectile which utilizes a plastic explosive that conforms to the surface of a target before detonating to improve the transfer of explosive energy to the target. Squash head projectiles are similar to high explosive projectiles and are well suited to many of the same targets. However, while HESH projectiles are not armor-piercing, they are capable of defeating armored targets by causing spall which can injure or kill a vehicle's occupants. They were fielded primarily by the British Army as the main explosive round of its main battle tanks during the Cold War. It was also used by other military forces, particularly those that acquired the early post-World War II British 105 mm Royal Ordnance L7A1 tank gun, including Germany, India, Israel and Sweden. In the United States, it is known as HEP, for "high explosive, plastic".
High-explosive anti-tank (HEAT) is a type of shaped charge explosive that uses the Munroe effect to penetrate heavy armor. The warhead functions by having an explosive charge collapse a metal liner inside the warhead into a high-velocity superplastic jet; this superplastic jet is capable of penetrating armor steel to a depth of seven or more times the diameter of the charge. The jet's effect is purely kinetic in nature; the round has no explosive or incendiary effect on the target.
Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure. Spalling and spallation both describe the process of surface failure in which spall is shed.
Sloped armour is armour that is neither in a vertical nor a horizontal position. Such angled armour is typically mounted on tanks and other armoured fighting vehicles (AFVs), as well as naval vessels such as battleships and cruisers. Sloping an armour plate makes it more difficult to penetrate by antitank-weapons, such as armour-piercing shells and rockets, if they follow a more or less horizontal trajectory to their target, as is often the case. The improved protection is caused by three main effects.
Armour-piercing discarding sabot (APDS) is a type of spin-stabilized kinetic energy projectile for anti-armour warfare. It consists of a sub-caliber round outfitted with a sabot to increase velocity compared to a full caliber round by firing a smaller lighter projectile from a relatively larger propellant-charge. The higher velocity gives the round increased penetration against armour. To not break at high speed impacts, APDS rounds traditionally features a hardened core made by tungsten or other hard material.
Bulletproof glass, ballistic glass, transparent armor, or bullet-resistant glass is a strong and optically transparent material that is particularly resistant to penetration by projectiles. Like any other material, it is not completely impenetrable. It is usually made from a combination of two or more types of glass, one hard and one soft. The softer layer makes the glass more elastic, so that it can flex instead of shatter. The index of refraction for both of the glasses used in the bulletproof layers must be almost the same to keep the glass transparent and allow a clear, undistorted view through the glass. Bulletproof glass varies in thickness from 3⁄4 to 3+1⁄2 inches.
An arrowhead or point is the usually sharpened and hardened tip of an arrow, which contributes a majority of the projectile mass and is responsible for impacting and penetrating a target, as well as to fulfill some special purposes such as signaling.
Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary physics, spallation describes meteoritic impacts on a planetary surface and the effects of stellar winds and cosmic rays on planetary atmospheres and surfaces. In the context of mining or geology, spallation can refer to pieces of rock breaking off a rock face due to the internal stresses in the rock; it commonly occurs on mine shaft walls. In the context of anthropology, spallation is a process used to make stone tools such as arrowheads by knapping. In nuclear physics, spallation is the process in which a heavy nucleus emits numerous nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight. In industrial processes and bioprocessing the loss of tubing material due to the repeated flexing of the tubing within a peristaltic pump is termed spallation.
Stopping power is the ability of a weapon – typically a ranged weapon such as a firearm – to cause a target to be incapacitated or immobilized. Stopping power contrasts with lethality in that it pertains only to a weapon's ability to make the target cease action, regardless of whether or not death ultimately occurs. Which ammunition cartridges have the greatest stopping power is a much debated topic.
Armor with two or more plates spaced a distance apart falls under the category of spaced armour. Spaced armour can be sloped or unsloped. When sloped, it reduces the penetrating power of bullets and solid shot, as after penetrating each plate projectiles tend to tumble, deflect, deform, or disintegrate; spaced armor that is not sloped is generally designed to provide protection from explosive projectiles, which detonate before reaching the primary armor. Spaced armour is used on armoured military vehicles such as tanks and combat bulldozers. In a less common application, it is used in some spacecraft that use Whipple shields.
Penetrating trauma is an injury that occurs when an object pierces the skin and enters a tissue of the body, creating an open wound. The penetrating object may remain in the tissues, come back out the way it entered, or pass through the tissues and exit from another area. An injury in which an object enters the body or a structure and passes all the way through is called a perforating injury, while penetrating trauma implies that the object does not pass through. Perforating trauma is associated with an entrance wound and an often larger exit wound.
The following are terms related to firearms and ammunition topics.
A gun is a ranged weapon designed to use a shooting tube to launch typically solid projectiles, but can also project pressurized liquid, gas or even charged particles. Solid projectiles may be free-flying or tethered. A large-caliber gun is also referred to as a cannon.
Beyond-armour effect is a term coined by Försvarets Fabriksverk (FFV), a semi-governmental Swedish defense firm, while developing the AT4. From the 1980s this phrase was used in its brochures, press releases, weapon instruction manuals and other documentation to denote the post-penetration effect of the AT4's HEAT anti-armour warhead against the interior and occupants of armoured vehicles.
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