Advanced Materials bring Fencing into the 20th Century
Background
The sport of fencing is one of only four to have featured at
every modern Olympic games. Until recently much of the
equipment used had changed relatively little since its inception, but lately
technological advances, and challenges to its Olympic status, have led to the
adoption of several innovative materials, with varying degrees of success.
Swords, masks and clothing have all seen changes, the most recent development
being the transparent mask, intended both to improve visibility for the
competitor, and make the sport more enjoyable for the spectator.
The Blade
There are three disciplines in modern fencing foil, epee and
sabre, each involving a different target area, employing a different weapon,
and demanding a different technique. A feature common to all three disciplines
is that the blades regularly break, turning a safe piece of sports equipment
into a potentially lethal weapon. Analysis of the fracture surfaces reveals the
characteristic features of fatigue crack growth, which is understandable given
that a successful attacking lunge can cause a blade to bend with a radius of
curvature in the region of 200mm. Repeated bending during a blade's lifetime,
coupled with surface damage from impacts with the opponent's blade, result in
the accumulation of damage in the form of microcracks,
which initiate fatigue failure. This is a particular problem with cheaper
blades made from medium carbon steel.
Blade Materials and
Manufacture
These blades are manufactured by quenching and tempering at
300 to 500°C, resulting in a tempered martensitic
structure with a yield stress of between 1500 and 1700MNm-2. A more expensive
foil material is maraging steel, which has a yield
stress in the region of 2000MNm-2 and an increased lifetime. The critical
defect size for fast fracture of the maraging steel
blades is over four times larger than in standard carbon steel types, which
explains the extended lifetime. However, although the lifetime of the maraging blades is longer, they still fail by brittle
fracture, resulting in a sharp edge that can penetrate the opponents clothing
and cause serious injury.
A variety of other materials have been investigated for the
foil, from glass and carbon fibre composites, to dual
phase steels that contain fibres of martensite with an interpenetrating austenite phase. This
dual phase steel material has demonstrated high strength and exceptional
toughness, with Charpy impact tests showing that
blade samples are able to absorb 360J impact energy without breaking into two
pieces, compared to 10J for conventional medium carbon steel blades. The
toughness originates from the inclusion of the austenite phase, which is
ductile under the impact conditions and deflects the crack along the length of
the blade, requiring re-initiation in an adjacent fibre
of martensite if the growth is to continue.
Surprisingly this grade of steel has never become a standard
production grade for fencing blades. Two reasons have been cited, one of which
is the higher cost, the other the different feel of the blade, which makes it
unpopular with fencers. The same explanations apply to glass and carbon fibre composite blades and, despite these investigations
into new materials for blades, conventional materials have not yet been
replaced.
Face Masks
This is not the case for the protective face masks used in
the sport. There has long been a desire within fencing to enable clear vision
of the opponent, something that is compromised by the current designs based on
a close metal mesh. Although numerous attempts have been made to replace the
metal designs over the years, no solution has offered any degree of consistent
safety or clarity of vision. The pace of development has quickened in recent
years due to threats from the International Olympic Committee to exclude
fencing from the games unless it modernised itself. A
key point in this demand was the need to make competitors' faces visible to
spectators and television audiences during competition. The IOC’s demand catalysed a development drive that had until that point
been very gradual.
Masks for the Future
Many fencing equipment manufacturers have responded to the
challenge to produce a clear mask, and one company that has been successful is
the UK-based manufacturer Leon Paul. The company has developed a clear mask
made from the Lexan grade of polycarbonate (figure
1), a polymer chosen for its combination of excellent optical clarity and high
impact resistance. The material is incorporated in two forms, a single 3mm
section covered with another layer 0.5mm thick. The thinner, disposable outer
layer protects the base layer from environmental stress cracking that could
occur on exposure to organic solvent. It also protects the base layer from the
effects of stress concentration due to blade damage on the surface of the mask.
Figure
1. The Leon Paul developed polycarbonate mask improves visibility
for the combatant and allows the audience to be more interactive compared to
the traditional mask on the right.
Tests at the Italian Fencing Federation laboratory comparing
metal and polymer masks have shown that the polymer sections outperformed the
conventional metal mesh sections. In drop tests from heights of 55cm with a
mass of 2.4kg fastened to a steel spike (section 3 x 3mm square, with a
pyramidal point angle of 60°) the metal mesh was penetrated, whereas the Lexan visor was only marked with an impression of the
pyramidal point. Tests on complete masks also showed that the Lexan based masks did not deform, while the metal mesh
versions did and to an extent deemed sufficient to injure the fencer. Although
the Olympic future of fencing is still uncertain the new mask technology will
certainly play a major role in preserving the current status of the sport.
Protective Clothing
A third area of fencing to evolve in recent years is the
protective clothing. Traditionally made from heavy gauge cotton fabric, the
advent of Kevlar led to protective panels being woven into the garments to
afford a high degree of localised protection.
However, Kevlar suffers from a major disadvantage. It degrades when washed in
biological washing powder or exposed to UV light. With due care and attention
there is no degradation in protection, but the legal implications of selling
such a garment encouraged manufacturers to look for alternatives. Today fencing
clothing is made from a blend of cotton and high strength polymer fibres such as ballistic nylon, a combination that affords
resistance to penetration of over 800N, and protection that is not localised.
Summary
These developments in materials technology are not only
increasing the safety of fencing, but also making the sport more enjoyable for
both competitors and spectators, and helping it to retain its Olympic status.
These issues are vitally important if the sport is to maintain its current
popularity.
Primary author: Dr. Mike Jenkins
Source: Materials World, vol. 8, pp. 9-10, September 2000
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