Background
The Division of Solid Mechanics at Lulea University
of Technology in
cooperation with Fallkniven AB has produced a testing methodology
to examine
the flexural strength of knives. Since the test is to re-create
authentic
conditions, no allowances have been made for factors such
as pull speed and pull distance in
the test, but the test concentrates
on applied load in the form of tensile load (kN)
and bending moment
(Nm). Based on this methodology, testing has been carried
out at the
laboratory of The Division of Solid Mechanics.
Experiment set-up
A tensile machine of the Dartec brand has been used
for the experiment,
capable of producing forces at ±250 kN. To this machine was applied
a
knife-holder and a wire to apply force upon the handle of the knife.
To secure
the locations of the wire on the knife handle, a screw brace
was applied to the
handle, so that the wire came between the jaws of
the brace and could run freely
in all directions except along the knife
handle. In this way, any uneven loads were
compensated for in
directions other than vertical. The abutments on the
knife-holder were
so formed as to compensate for knife blades of different thickness
and in order to give a well-defined breaking point independent of the
bending of
the knife blade.
Testing
Testing was carried out under controlled conditions
with a constant
pull speed of 1mm/sec., which gave a varying force. The testing was
carried
out at a constant temperature of 20°C (68°F). The length of
the tested knives
varied a good deal, and therefore it was decided
to set the breaking point at 30 %
along the blade reckoned from the
tip, at the point where the blade reaches its
full thickness and width.
A basic load of 100N was applied to the knives, except
for knife
WM1, which was subjected to a load of 50N, owing to its small size.
Result
The result are presented in a diagram with the shift
in the X-axis and
the load and bending moment in the Y-axis for each knife.
The bending moment
was calculated by multiplying the load (kN)
by the distance (m) between the
contact points of the wire against
the knife handle and the breaking point in the
abutment.
For comparison, the break load has been transposed from Newton
force to the
corresponding weight in kg.
Number of kilos = Number of N/9.81.
The following graphs show the result for the Fallkniven
models
A1,A2 Lam, F1, F1 Lam, S1 and WM1.
April 28, 2000
Jan Granstrom
Division of Solid Mechanics
The Technical University of Lulea
Discussion
When it comes to knives for survival use, one of the most
important
requirements is that the knife should be strong. The figures and graphs
above show how strong these four knives are. What says most
about
the strength of a knife is at which bending moment (torque) the knife
breaks.
Discuss in this way:
Mod. A1 breaks at a load of 2,375 N (or a weight of 242 kg/556
lbs)
when the tested length is 150 mm (6").
If you make a knife longer, you will need less load or power for
breaking
it but the bending moment (torque) is just the same. This
circumstance
(the fact that the torque is the same) makes it possible to compare knives
with each other with regard to the strength quality.
Factors which determine the strength of a knife are its blade
length, blade
thickness (blade geometry), steel quality and technical design. A
long
blade gives you more power, a thick, sturdy blade is stiffer,
a well-treated high-end steel stands strain better and a well-designed
knife is free from natural breaking zones.
Depending on what you want from a knife you should consider
these
qualities before you make your purchase, only then will you be able to
make the optimal choice.
Our knives are designed to serve as standard knives under
normal
conditions, but stand much more than everyday use normally
demands if you are suddenly forced to rely upon the strength, edge
retention and design of the knife. These knives are the result of
a
superoptimized combination of a high-end steel (VG10) and an
accomplished technical, purposeful, ergonomic design.
Peter Hjortberger
|
