Rolled homogeneous armour
Encyclopedia
Rolled homogeneous armour (RHA) is a type of steel which is used to armour vehicles
.
RHA is called homogeneous armour because its structure and composition is uniform throughout its section. The opposite of homogeneous steel plate is face-hardened steel plate, where the face of the steel is composed differently to the substrate. The face of the steel, which starts as an RHA plate, is hardened by a heat-treatment process.
RHA was in universal use during this period and the measure of the power of an anti-tank gun was the thickness of RHA it would penetrate. This measure of tank gun effectiveness has remained in use because it is a useful universal measure for the comparison of increased anti-tank gun effectiveness. Different types of armour, some of which do not use steel or even metals, have come into use but depth of penetration of RHA is still used to compare anti-tank weapon effectiveness.
RHA was in common use until after World War II
when other types of armour were being developed. A new generation of anti-tank rounds had come into use which did not use a heavy, tough, high-velocity projectile, to defeat steel armour but used an explosive charge called a shaped charge
to overcome the strength of the steel. The strength, toughness and hardness of RHA was no longer protection against this threat.
, because of a reduction in effectiveness against new attack methods (mainly shaped charge
s and improved kinetic energy penetrators), RHA has been superseded by composite armour
, which incorporates air spaces and materials such as ceramic
s or plastic
s in addition to steel, and explosive reactive armour
.
For the purposes of testing and calibration of anti-tank guns, the term RHAe (Rolled Homogeneous Armour equivalency) is used when giving an estimate of either the penetrative capability of a projectile
or the protective capability of a type of armour
which may or may not be steel
. Because of variations in armour shape, quality, material, and case-by-case performance, the usefulness of RHAe in comparing different armour is only approximate.
Currently, most armoured vehicles have their basic structure formed from RHA to lend general strength and toughness against general threats. Over this RHA is added the new types of armour.
use, RHA is produced to military standard MIL-DTL-12560 by several manufacturers. Another standard is MIL-DTL-46177; however, this standard has been inactivated, and all new designs should use MIL-DTL-12560. MIL-DTL-46177 RHA is similar to SAE 4340 steel alloy.
Vehicle armour
Military vehicles are commonly armoured to withstand the impact of shrapnel, bullets, missiles, or shells, protecting the personnel inside from enemy fire. Such vehicles include tanks, aircraft, and ships....
.
Composition
Armoured steel must be hard yet impervious to shock in order to resist high velocity metal projectiles. Steel with these characteristics is produced by processing cast steel billets of appropriate size and then rolling them into plates of required thickness. Hot rolling homogenizes the grain structure of the steel, removing imperfections which would reduce the strength of the steel. Rolling also elongates the grain structure in the steel to form long lines, which enable the stress under which the steel is placed when loaded to flow throughout the metal, and not be concentrated into one area.RHA is called homogeneous armour because its structure and composition is uniform throughout its section. The opposite of homogeneous steel plate is face-hardened steel plate, where the face of the steel is composed differently to the substrate. The face of the steel, which starts as an RHA plate, is hardened by a heat-treatment process.
History
From the invention of tanks through to the Second World War, tank armour increased in thickness to resist the increasing size and power of anti-tank guns. A tank with sufficient RHA could resist the largest anti-tank guns then in use.RHA was in universal use during this period and the measure of the power of an anti-tank gun was the thickness of RHA it would penetrate. This measure of tank gun effectiveness has remained in use because it is a useful universal measure for the comparison of increased anti-tank gun effectiveness. Different types of armour, some of which do not use steel or even metals, have come into use but depth of penetration of RHA is still used to compare anti-tank weapon effectiveness.
RHA was in common use until after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
when other types of armour were being developed. A new generation of anti-tank rounds had come into use which did not use a heavy, tough, high-velocity projectile, to defeat steel armour but used an explosive charge called a shaped charge
Shaped charge
A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to cut and form metal, to initiate nuclear weapons, to penetrate armor, and in the oil and gas industry...
to overcome the strength of the steel. The strength, toughness and hardness of RHA was no longer protection against this threat.
Present use of RHA
Since World War IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, because of a reduction in effectiveness against new attack methods (mainly shaped charge
Shaped charge
A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to cut and form metal, to initiate nuclear weapons, to penetrate armor, and in the oil and gas industry...
s and improved kinetic energy penetrators), RHA has been superseded by composite armour
Composite armour
Composite armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armour are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration...
, which incorporates air spaces and materials such as ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s or plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s in addition to steel, and explosive reactive armour
Reactive armour
Reactive armour is a type of vehicle armour that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. It is most effective in protecting against shaped charges and specially hardened long rod penetrators...
.
For the purposes of testing and calibration of anti-tank guns, the term RHAe (Rolled Homogeneous Armour equivalency) is used when giving an estimate of either the penetrative capability of a projectile
Projectile
A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....
or the protective capability of a type of armour
Armour
Armour or armor is protective covering used to prevent damage from being inflicted to an object, individual or a vehicle through use of direct contact weapons or projectiles, usually during combat, or from damage caused by a potentially dangerous environment or action...
which may or may not be steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
. Because of variations in armour shape, quality, material, and case-by-case performance, the usefulness of RHAe in comparing different armour is only approximate.
Currently, most armoured vehicles have their basic structure formed from RHA to lend general strength and toughness against general threats. Over this RHA is added the new types of armour.
Specifications
For current United States ArmyUnited States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...
use, RHA is produced to military standard MIL-DTL-12560 by several manufacturers. Another standard is MIL-DTL-46177; however, this standard has been inactivated, and all new designs should use MIL-DTL-12560. MIL-DTL-46177 RHA is similar to SAE 4340 steel alloy.
See also
- Sloped armourSloped armourSloped armour is armour that is neither in a vertical nor a horizontal position. Such "angled" armour is often mounted on tanks and other armoured fighting vehicles...
- Composite armourComposite armourComposite armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armour are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration...
- Reactive armourReactive armourReactive armour is a type of vehicle armour that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. It is most effective in protecting against shaped charges and specially hardened long rod penetrators...
- Vehicle armourVehicle armourMilitary vehicles are commonly armoured to withstand the impact of shrapnel, bullets, missiles, or shells, protecting the personnel inside from enemy fire. Such vehicles include tanks, aircraft, and ships....
- Slat armour
External links
- Bibliography of Tank Armor Internet ArchiveInternet ArchiveThe Internet Archive is a non-profit digital library with the stated mission of "universal access to all knowledge". It offers permanent storage and access to collections of digitized materials, including websites, music, moving images, and nearly 3 million public domain books. The Internet Archive...
Wayback MachineWayback MachineThe Wayback Machine is a digital time capsule created by the Internet Archive non-profit organization, based in San Francisco, California. It is maintained with content from Alexa Internet. The service enables users to see archived versions of web pages across time, which the Archive calls a "three...
link change on May 10, 2009. Contains alloy compositions of military specification armor steels.