United States of America (1983-1992)
Infantry Fighting Vehicle – 1 Turret & Hull Built
The pressure on armored vehicle designers to keep down weight without compromising protection or performance is great. Much focus has been made on moving away from traditional steel armor to aluminium or even titanium and ceramics as an alternative. Whilst these can improve weight without reducing protection, they come with an often very steep price tag as well as other problems. One idea from the early 1980s was the possibility of using a new generation of fiber-reinforced plastics to form the hull of armored fighting vehicles, which led to the creation of a composite body M113 Armoured Personnel Carrier (APC). Whilst the M113 was already obsolete and being replaced with the M2 Bradley Infantry Fighting Vehicle (BIFV), the glass fiber composite technology had shown the potential of not just reducing weight of the new APC but also of increasing protection at the same time. The composite used on the M113 was rather basic and would be improved with the first generation of integrated ceramics to provide improved ballistic protection.
At the same time, Food Machinery Corporation (FMC) of San Jose, California, the parent firm for the M113, undertook the development of a composite turret for the Bradley with the project starting in 1983, manufacturing 5 turrets by the middle of 1987. Unlike the ‘double sandwich’ of the hull used on the M113, this turret composite was a single layer of polyester bonded S-glass. Overall, the turret was identical in shape and layout to the standard M2 Bradley turret except that it was made in two halves with the resin impregnated glass fiber cloth and then joined together with a metal frame. Making the turret out of S-2 glass fiber/polyester resin composite saved 15% over the weight of the original turret structure with similar levels of ballistic protection. This turret design was then sent for firing trials at Camp Roberts, California, in Autumn 1986. These appear to have been successful, as, by September that year, FMC was awarded a further contract from the US Army Materials Technology Laboratory (M.T.L.), Watertown, Massachusettes to develop this idea further with a composite hull for the entire vehicle.
This hull is referred to technically as Glass Reinforced Polyester (GRP) hull, but often shortened simply to ‘plastic’. The structure of this vehicle was essentially the same as that of the composite turret, consisting of just a polyester bonded S-2 glass fiber, and fabricated in two halves (with the floor panel as a single piece rather than having a seam) which were then joined together using an aluminium alloy frame. Unlike the early tests of the composite M113, this was simpler to produce, lacking the ‘sandwiching’ of the earlier trials. Metal was not eliminated completely either from the prototype, as the turret ring remained metal, as did many of the fittings and the whole rear ramp arrangement. The aluminium frame providing the stiffness for the hull and to which the halves were attached also served as the attachment point for the suspension arms. The hull construction consisted of a floor deck and two side panels, each 2.4m x 6.7m fabricated from plies of S-2 glass fiber in polyester resin ranging from 22 to 69 plies thick. After fabrication and post-manufacture finishing, each panel weighed just 820 kg, a saving of 25% over the original metal structural panels. Work on the composite turret would be less successful and indicate that switching out just the aluminium-armour parts for composites could result in a weight saving of 15.5%.
Unlike the marginal improvements with the M113 composite hull, the weight saving for the Bradley composite was large, 27% lighter than the standard hull, even with the additional ceramic exterior tiles as applique armor.
Just like the turret, the hull was tested ballistically too. In terms of protection, it was more resistant against explosive blasts and more resistant to spalling than the standard M2 Bradley. The tests had been successful and significant savings in weight could be made, although the cost of mass production of such hulls, not to mention longevity issues, were still to be addressed. One additional advantage of the plastic hulled vehicle was that it had better thermal properties than the metal hull. It stayed cooler and was less prone to overheating, providing better insulation. On paper at least, it was successful enough that in 1992 a new project was started known as the Composite Armored Vehicle (CAV), intended to develop the technologies needed to produce a range of composite hulled military vehicles. That project was developed by United Defence as the third generation of their program of ceramic composite armor development with the Bradley constituting generation 1 and the M8 AGS, generation 2.
Protection
With the majority of the aluminium hull replaced with the S-2 glass fiber composite, the vehicle had structure but lacked the ballistic protection required to protect against the Russian 14.5 mm round. As a result, the vehicle was designed to take special ceramic tiles bolted to the outside. These tiles were made from TiB2 (titanium diboride), an extremely hard material (1800 Knoop, a hardness test unit for very thin or brittle materials) with a high melting point (2970 Celsius) and high density (4.52 g/cm3). Compared to steel with a density of 7.85g/cm3 and aluminium 5083 armor with a density of just 2.66g/cm3, TiB2 lay half way between the two materials but was more than ten times harder than aluminium (1800 Knoop vs 109 Knoop). These rectangular tiles were overlaid with each other in a ‘brick’ weave pattern.
Problems
Ignoring issues with the weight, there was a more fundamental problem with the composite body for the M2 Bradley. Just as was found during the same tests with the composite body for the M113, the new plastic hulls exhibited significant longitudinal twisting during testing. In comparative testing though, the small M113 came out better than the larger M2 Bradley in this regard. When fitted with engine, hatches and equipment etc., it simply showed less twisting along the longitudinal axis. Both designs showed themselves equally good at absorbing vibrations, with the plastic hull better than the metal versions.
The completed FMC Composite M2 Bradley Infantry Fighting Vehicle (BIFV) was shown off to 200 assorted military, media, and FMC representatives in June 1989 when it was unveiled by General Louis Wagner, then head of the US Army’s Materiel Command. From this public unveiling, it was taken to Camp Roberts in California for 6,000 miles (9,656 km) testing under real-world conditions. Optimistically at the time, the composite BIFV was seen as being able to deliver a 25% weight saving along with improvements to vibration, noise reduction (10dB), reducing spall, lower radar signature, improved thermal efficiency, improved protection against mines and a 20% saving in the cost of manufacture along with lower life-cycle costs. Certainly, these were very exciting potential benefits and they were, overall, somewhat successful. The composite M2 BIFV never went into production though, the hull could still be improved, the external ceramic tiles were too vulnerable to damage and, as with all composites, the issues of repair and multi-shot resistance were not addressed. Instead, a new project was started in 1992 – the Composite Armored Vehicle (CAV) program. This would require the manufacture of a completely new vehicle as a demonstrator test-bed for composite armors known as the Advanced Technology Demonstrator (ATD) as part of the US Army’s Thrust program. More than one company submitted bids for a new composite hulled vehicle platform for the US Military but the program faded out. The work on proving the technology on the M113 and then on the M2 Bradley was to evolve and find use in the CAV-ATD program, but the Composite M2 was not adopted. The fate of the prototype M2 Composite hull is not known.
Illustration of the Composite M2 Bradley modified by Pavel Alexe based on work by David Bocquelet, funded by our Patreon campaign.
Sources
Bradley: A history of American fighting and support vehicles. (1999) R.P. Hunnicutt, Presidio Press
Modal Analysis of the M113 Armored Personnel Carrier Metallic Hull and Composite Hull. (1995). Morris Berman. Army Research Laboratory
Aluminium 5083. (2018). ASM Aerospace Specification Metals Inc.
Ceramic Armor Materials by Design. (2012). James McCauley, Andrew Crowson, William Gooch, A. Rajendran, Stephen Bless, Kathryn Logan, Michael Normandia, Steven Wax. Ceramic Transactions Series No.134
Fourteenth International Conference Proceedings. (1999). American Society of Composites.
Composite Fighting Vehicle ‘Rolled Out’. (1989). Carrick Leavitt. UPI
Army Research, Development and Acquisition Bulletin, January-February 1990
Advanced Composite Materials. (1994). Louis Pilato, Michael Michno, Springer-Verlag, Berlin