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09/02/2012
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Manufacturers have long sought to improve the durability and performance of automotive brake discs, which are subject to tremendous temperature and pressure changes. The current range of brake discs are mostly made from cast iron, except for very high performance discs which are made up of a ceramic composite.
 At present, cast iron discs are used on many standard cars but these are both heavy and relatively underperforming when compared to the more advanced cermic composite brakes. However, due to the expense, ceramic brakes are usually reserved for the likes of high performance road and track cars, and competitive racing cars.
Although cast iron brake discs offer strength, they are heavy and have a far from perfect operating profile. Iron also does not adapt well to the demands placed on different sections of the disc and rotor. A brake disc usually has three functional zones, each of which requires a material with distinct strain and thermal properties to function optimally. Temperature and pressure changes across the surface are often a major cause of wear, warpage and potential failure.
As a result, US researchers from the Polytechnic Institute of New York University have teamed up with aerospace and transportation component supplier, REL, to find a better solution. The aim is to use a lightweight material, that enables high-performance braking but at a similar cost to cast iron brakes.
Adam Loukus, vice president of REL, says: "As auto companies strive to meet increasingly high efficiency and low emissions targets, there's a tremendous business opportunity in creating novel, lightweight components that reduce overall vehicle weight and increase vehicle performance."
The team is developing a one-piece brake rotor uniquely tailored to meeting the extreme and variable temperature and loading conditions experienced by a typical car over its lifetime. REL received a $150,000 research grant to develop the initial product design, material and manufacturing process. It was given the brief to produce fibre reinforced metal matrix composite (MMC) brake rotors, that are aimed at the mass market and are therefore easy to manufacture.
The team replaced the traditional material with a high-temperature aluminium alloy reinforced with functionally-graded ceramic particles and fibres to create a lightweight, but extremely durable material. This combination of material also permits the ability to customise the composite to best suit each section of the disc and rotor. The result was a brake disc that weighs 60% less than a cast iron alternative but with triple the life expectancy.
Professor Nikhil Gupta from the Polytechnic Institute of New York University, says: "The hybrid material allows us to provide reinforcement where additional strength is needed, increase high temperature performance, and minimise stress at the interfaces between the zones. Together, this should boost [disc] life significantly, reducing warranty and replacement costs, and the weight savings will improve the vehicle's fuel efficiency."
In addition to the automotive market, metal matrix composite brake discs have a great deal of transferability in to other vehicles; from bikes to military vehicles. The team is in the process of researching the other possibilities including work on some military fleets, where 'up-armoured' vehicles operate at weights well above their design capacity. While the development of lightweight armour remains a long-term goal for the military, any weight savings on the vehicles themselves will immediately improve fleet efficiency, which can be critical to mission success.
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Author
Justin Cunningham
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