Karting

Anales de la Mecánica de Fractura, Vol 1 (2007)
SUB -CRITICAL CRACK GROWTH IN HIGHLY STRESSED FORMULA 1 RACE CAR COMPOSITE
SUSPENSION COMPONENTS
Gary Savage
Honda Racing F1 Team
ABSTRACT
One of the many advantages in the use of composite materials in engineering structures is their resistance to fatigue.
Careful component design means that complex, weight-efficient components can beproduced which are “intrinsically
safe” in that they have an effectively infinite fatigue life. Excessive loading and manufacturing/design details may,
however, invoke a process analogous to fatigue in metal components leading to ultimate failure of the component at a
load below its design limit. A somewhat qualitative analysis has shown this mechanism to result primarily due to subcritical
crackgrowth within the resin matrix material. Although the phenomena need further investigation, it was found
that the crack growth could be suppressed by using a resin matrix with a much higher toughness. A short introduction
to the use of composite materials in formula 1 is given along with a discussion to illustrate how the practical application
of Materials Science and Fracture Mechanicsprinciples were used to solve a potentially serious problem.
1. COMPOSITE MATERIALS IN FORMULA 1
In Formula One, weight saving is all-important. Despite
the governing body imposing a minimum weight limit,
teams still spend much of their time trying to hone
components to the lowest possible weight. This is
because dropping below the minimum weight allows
them to redistribute weight around the car inthe form of
ballast. Vehicle dynamics studies have shown the
benefits in controlling the vehicle’s mass distribution
upon its handling. As a consequence every component
on an F1 car must be engineered to the absolute
minimum weight. The more ballast that is needed to
return the car to the legal minimum weight, the more
scope is provided to achieve optimum performance by
tuning its balanceby appropriate positioning of said
ballast Half a kilo taken off the rollover hoop, for
example, and added to the bottom of the car in ballast
lowers the centre of gravity and can be worth up to a
tenth of a second. Such fractions of a second are hard
fought for. Every team is constantly looking for ways to
get ahead or simply keep up. It is this intense level of
competition that fuels thefrantic pace of development
in formula one. There is therefore an incentive to use
weight efficient materials; particularly fibre reinforced
composites, wherever possible.
Carbon fibre composites were first used in Formula 1 in
1980, when McLaren Technical Director John Barnard
designed and built the first carbon fibre chassis (1).
Barnard was attracted to carbon fibre, which at the timewas used almost exclusively by the aerospace industry,
because of its incredibly high specific stiffness. He
correctly postulated that carbon fibres could offer a
huge step both in chassis stiffness and weight reduction.
His composite McLaren MP4-1 (Figure 1)
revolutionised the world of racing car design when it hit
the track in 1981, despite his detractors initially
dismissing the idea ofusing such brittle materials in
race car construction. By 1984 however, the whole of
Formula 1 had jumped on the carbon fibre bandwagon.
Barnard’s concept has today been accepted as the
industry standard in all types of formula racing car
design. In fact, so established is the practice that the
FIA’s current Formula 1 technical regulations are
written in such a way that it would be verydifficult to
make a chassis out of anything else. During the design
of the MP4/1, Barnard used carbon composites
wherever they offered advantages in mechanical
properties or a reduction in complexity of design. Since
that time there has been a continual process of metals
replacement within the sport. In the early 1990s, Savage
and Leaper from McLaren developed composite
suspension members...