Perisai Chobham

Dari Wikipedia Bahasa Melayu, ensiklopedia bebas.

Perisai Chobham merupakan nama tidak rasmi bagi perisai sebatian yang dibangunkan pada 1960-an oleh pusat penyelidikan kereta kebal British bagi Chobham Common. Nama ini kini menjadi istilah generik bagi perisai kenderaan seramik.

Sungguhpun perincian pembinaan perisai Chobham Common kekal rahsia, ia telah digambarkan sebagaia sebatian terdiri daripada jubin seramik diselitupi matrix logam dan dilekatkan pada kepingan belakang dan beberapa lapisan anjal. Disebabkan seramik yang digunakan amat keras, ia menawarkan ketahanan lebih terhadap peletup bentuk (shaped charge) seperti peluru Peletup Kuat Anti-Kereta kebal (High Explosive Anti-tank) (HEAT) dan ia menghancurkan perobek tenaga kinetik (kinetic energy penetrator).

Senarai kandungan 1 Struktur 2 Protective qualities 3 Disadvantages 4 Development and application 5 Nota 6 Rujukan 7 Bacaan lanjut 8 Pautan luar

[sunting] Struktur

Jubin seramik mempunyai masaalah "keupayaan hentaman berganda" di mana ia tidak mampu menahan hantaman bertalu tanpa kehilangan nilai perlindungannya dengan pantas.^[1] Untuk mengurangkan kesan ini jubin dihasilkan sekecil mungkin, tetapi unsur matrix mempunyai ketebalan minima pratikal sekitar satu inci / 25 mm. dan nisbah perlindungan diberikan jubin akan menjadi tidak diingini, meletakkan had pada diameter sekitar sepuluh sentimeter. Jubin kecil segi empat atau hexagon dikelilingi matris samaada melalui tekanan secara isostatik kedalam matrix yang dipanaskan,^[2] atau dengan mengamkannya menggunakan resin epoxy. Sejak awal sembilan puluhan ianya telah diketahui bahawa meletakkan jubin dibawah tekanan sekata oleh matricnya meningkatkan ketahanan kepada perobek kinetik dengan banyak, yang sukar dicapai apabila menggunakan gam.^[3]

Matrix perlu dilapis dengan kepingan, bagi memperkukuhkan jubin seramik di belakang dan menghalang matrix logam reyuk oleh hentaman kinetik. Biasanya kepingan pelapis adalah separuh dari jisim matrix sebatian.^[4] Pemasangan ini kemudian dipasang pada lapisan anjal. Ini menyerap sebahagian hentaman, tetapi fungsi utamanya adalah bagi meningkatkan hayat perkhidmatan matrix dengan melindungnya dari getaran. Beberapa pemasangan boleh ditindan, bergantung kepada ruang yang ada; dengan ini perisai boleh dibentuk secara modular, boleh disesuaikan dengan keadaan. Ketebalan pemasangan biasa masa kini adalah antara lima dan enam sentimeter.

Tolong bantu menterjemahkan sebahagian rencana ini. Ini memerlukan kemaskini dalam Bahasa Melayu piawai Dewan Bahasa dan Pustaka. Silalah membantu, bahan-bahan boleh didapati di en:Perisai Chobham. Sumber-sumber bantuan: Kamus Dewan Bahasa.

The armour configuration of the first western tanks using Chobham armour was optimised to defeat shaped charges as guided missiles were seen as the greatest threat. In the eighties however they began to face improved Soviet kinetic energy penetrator rounds of various sorts, which the ceramic layer was not particularly effective against: for the original ceramics the resistance against penetrators was about three times, for the newest composites it is about ten times less than against HEAT rounds. For this reason many modern designs include additional layers of heavy metals to add more density to the overall armour package.

The introduction of more effective ceramic composite materials allows for a larger width of these metal layers within the armour shell, given a certain protection level provided by the composite matrix. They typically form an inner layer placed below the much more expensive matrix^[5], to prevent extensive damage to it should the metal layer strongly deform but not defeat a penetrator. They can also be used as the backing plate for the matrix itself, but this compromises the modularity and thus tactical adaptability of the armour system; furthermore, due to their extreme hardness, they deform insufficiently and would reflect too much of the impact energy to the ceramic tile. Metals used include a tungsten alloy for the Challenger 2^[6] or, in the case of the M1A1HA (Heavy Armor) and later American tank variants, a depleted uranium alloy^[7].

Some companies offer titanium carbide modules. These metal modules (typically employing perpendicular rods) have many perforations or expansion spaces reducing the weight up to about a third while keeping the protective qualities fairly constant. The depleted uranium alloy of the M1 has been described as "arranged in a type of armour matrix"^[8] and a single module as a "stainless-steel shell surrounding a layer (probably an inch or two thick) of depleted uranium, woven into a wire-mesh blanket"^[9].

Such modules are also used by tanks not equipped with Chobham armour. The combination of a composite matrix and heavy metal modules is sometimes informally referred to as "second generation Chobham"^[10].

---

>

[sunting] Protective qualities

Due to the extreme hardness of the ceramics used, they offer superior resistance against a shaped charge jet and they shatter kinetic energy penetrators. The (pulverised) ceramic also strongly abrades any penetrator. Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will within a certain velocity range (the "gap") not lead to a deeper penetration but destroy the projectile itself instead^[11] . Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth — as it would be when penetrating a metal — but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection"^[12]. This mechanism using the jet's own energy against it, has caused some to compare the effects of Chobham to those of reactive armour. This should not be confused with the effect used in many laminate armour of any kind: that of sandwiching an inert but soft elastic material such as rubber, between two of the armour plates. The impact of either a shaped charge jet or long-rod penetrator, after the first layer has been perforated and the rubber layer is being penetrated, will cause the rubber to deform and expand, so deforming both the back and front plates. Both attack methods will suffer from obstruction to their expected paths, so experiencing a greater thickness of armour than is there is nominally, thus lowering penetration. Also for rod penetrations, the transverse force experienced due to the deformation may cause the rod to shatter, bend, or just change its path, again lowering penetration.

The effectiveness of Chobham armour was demonstrated in the Gulf Wars of 1991 and 2003, where no Coalition tank was destroyed by either the obsolete Iraqi armour or ATGWs. In some cases the tanks in question were subject to multiple hits by both KE-penetrators and HEAT rounds, but the old Russian ammunition used by the Iraqis, in their Polish licence built T-72s, their old T-55s bought from Russia and upgraded with "Enigma" type armour, and T-62 tanks left them completely incapable of penetrating the front armour of Coalition tanks. It is also worth noting that the Iraqis rarely actually hit the Coalition tanks, because of lack of training and inferior optics. To date, only 5-10 Chobham-protected tanks have been defeated by enemy fire in combat, including an M1 that was hit on the side skirts, below the turret ring by a PG-7VR, a tandem charge RPG, in the Iraq War. The jet penetrated the skirting armour and side hull armour, then traversed across the tank's interior and finally penetrated 1.5 to 2 inches into the hull armour on the other side.

[sunting] Disadvantages

The armour's very effectiveness is relative to its cost and so this in-itself has become a potential weapon of war – an economic war. The Iraq War has seen insurgents target tanks with RPGs and IEDs and while rarely destroying them outright, the cost of repair has imposed its own strain on the military.^[13]

[sunting] Development and application

Since the early sixties there were in the USA extensive research programmes ongoing aimed at investigating the prospects of employing composite ceramic materials as vehicle armour^[14]. This research mainly focused on the use of an aluminum metal matrix composite reinforced by silicon carbide whiskers, to be produced in the form of large sheets.^[15] The reinforced light metal sheets were to be sandwiched between steel layers.^[16] This arrangement had the advantage of having a good multiple-hit capability and of being able to be curved, allowing the main armour to benefit from a sloped armour effect. However, this composite with a high metal content was primarily intended to increase the protection against KE-penetrators for a given armour weight; its performance against shaped charge attack was mediocre and would have to be improved by means of a laminate spaced armour effect, as researched by the Germans within the joint MBT-70 project^[17].

An alternative technology developed in the USA was based on the use of glass modules to be inserted into the main armour;^[18] although this arrangement offered a better shaped charge protection, its multiple hit capability was poor. A similar system using glass inserts in the main steel armour was from the late fifties researched for the Soviet Obiekt 430 prototype of the T-64;^[19] this was later developed into the "Combination-K" type, having a ceramic compound mixed with the silicon oxide inserts, which offered about 50% better protection against both shaped charge and KE-penetrator threats, compared with a steel armour of the same weight.^[20] It was, later in improved forms, part of all subsequent Soviet main battle tank designs. After an initial period of speculation in the West as to its true nature, the characteristics of this type were disclosed when the dissolution of the Soviet Union and the introduction of a market system forced the Russian industries to find new customers by highlighting its good qualities;^[21] it is today rarely referred to as Chobham armour.

Meanwhile in the United Kingdom another line of ceramic armour development had been started, meant to improve the existing cast turret configuration of the Chieftain that already offered excellent heavy penetrator protection; the research by a team headed by Gilbert Harvey of the Fighting Vehicles Research and Development Establishment, was thus strongly oriented at optimising the ceramic composite system for defeating shaped charge attack^[22]. The British system consisted of a honeycomb matrix with ceramic tiles backed by ballistic nylon^[23], placed on top of the cast main armour.^[24] In July 1973 an American delegation, in search of a new armour type for the XM815 tank prototype, now that the the MBT-70 project had failed, visited Chobham Common to be informed about the British system. It was very impressed by the excellent shaped charge protection combined with the penetrator impact damage limitation, inherent to the principle of using tiles. The Ballistic Research Laboratory at the Aberdeen Proving Ground that year initiated the development of a version, named Burlington, adapted to the specific American situation with a much higher projected tank production run and the use of a thinner rolled steel main armour. The increased threat posed by a new generation of Soviet guided missiles armed with a shaped charge warhead — as exemplified by the events of the Yom Kippur War of October 1973, when even older generation missiles caused considerable tank losses on the Israeli side — made Burlington the preferred choice for the armour configuration of the XM1 (the renamed XM815) prototype.^[25]

However, on 11 December 1974 a Memorandum of Understanding was signed between the Federal Republic of Germany and the USA about the common future production of a main battle tank; this made any application of Chobham armour dependent on the eventual choice for a tank type. Earlier in 1974 the Americans had asked the Germans to redesign the existing Leopard 2 prototypes, considered by them too lightly armoured and had suggested to adopt Burlington for this purpose; the Germans however in response that year initiated a new armour development programme of their own.^[26] Having already designed a system that in their opinion offered satisfactory protection against shaped charges, consisting of multiple laminate spaced armour with the spaces filled with ceramic polystyrene foam^[27] as fitted to the Leopard 1A3, they put a clear emphasis on improving KE-penetrator protection reworking the system into a perforated metal module armour. A version with added Burlington was considered, including ceramic inserts in the various spaces, but rejected as it would push vehicle weight well over sixty metric tonnes, a weight then seen as prohibitive by both armies^[28]. The US Army in the summer of 1974 faced the choice between the German system and their own Burlington, a decision made more difficult by the fact that Burlington offered, compared with steel armour, no weight advantage against KE-penetrators:^[29] the total armour system would have a RHA equivalence against them of about 350 mm (compared to about 700 mm against shaped charges).^[30] No consensus developing, General Creighton Abrams himself decided the issue in favour of Burlington.^[31] Eventually each army would procure its separate national tank design, the project of a common tank failing in 1976. In February 1978 the first tanks protected by Burlington left the factory when the first of eleven pilot M1 tanks were delivered to the US Army.

In the United Kingdom application of Chobham armour was delayed by the failure of several advanced tank projects: first that of a joint German-British main battle tank; then the purely British MBT-80 programme. The Iranian government had ordered 1,225 vehicles of an upgraded Chieftain type, the Shir-2 (FV 4030/3), with Chobham armour added to the main cast armour, bringing total weight to 62 metric tonnes. When this order was cancelled in February 1979 because of the Iranian Revolution, the British government, under pressure to modernise its tank fleet to maintain a qualitative superiority relative to the Soviet tank forces, decided to use the sudden surplus production capacity to procure a number of vehicles very close in design to the Shir-2, called the Challenger 1. On 12 April 1983 the first British tank protected by Chobham armour was delivered to the Royal Hussars.

The latest version of Chobham armour is used on the Challenger 2 (called Dorchester armour), and (though the composition most probably differs) the M1 Abrams series of tanks, which according to official sources is currently protected by silicon carbide tiles. Given the publicly stated protection level for the earliest M1: 350 mm steel equivalence against KE-penetrators (APFSDS), it seems to have been equipped with alumina tiles.Templat:Or

Though it is often claimed to be otherwise, the Leopard 2 in fact does not use Chobham armour, but pure perforated armour, avoiding the very large procurement, maintenance and replacement costs of those ceramic armour systems not based on the cheap but rather ineffective alumina. For many modern tanks, such as the Japanese Type 90 and the Italian Ariete, it is yet unknown which type is used. There is a general trend away from ceramic armour towards perforated armour; but even many tanks from the seventies like the Leopard 1A3 and A4, the Italian OF-40 and the French AMX-32 and AMX-40 prototypes used the latter system; the Leclerc has an improved version.

---

>

[sunting] Nota

[sunting] Rujukan

[sunting] Bacaan lanjut

• Jeffrey J. Swab (Editor), Dongming Zhu (General Editor), Waltraud M. Kriven (General Editor); Advances in Ceramic Armor: A Collection of Papers Presented at the 29th International Conference on Advanced Ceramics and Composites, January 23-28, 2005, Cocoa Beach, Florida, Ceramic Engineering and Science Proceedings, Volume 26, Number 7; ISBN 1-57498-237-0

[sunting] Pautan luar

• Article on DSTL/QinetiQ Chertsey and Longcross Test Track (Chobham Tank Research Centre)