Abstract:
There is now a widely accepted need for stab resistant body armour for the police in
the UK. However, very little research has been done on knife resistant systems and
the penetration mechanics of sharp projectiles are poorly understood. This thesis
explores the general background to knife attack and defence with a particular
emphasis on the penetration mechanics of edged weapons.
The energy and velocity that can be achieved in stabbing actions has been determined
for a number of sample populations. The energy dissipated against the target was
shown to be primarily the combined kinetic energy of the knife and the arm of the
attacker. The compliance between the hand and the knife was shown to significantly
affect the pattern of energy delivery. Flexibility and the resulting compliance of the
armour was shown to have a significant effect upon the absorption of this kinetic
energy.
The ability of a knife to penetrate a variety of targets was studied using an
instrumented drop tower. It was found that the penetration process consisted of three
stages, indentation, perforation and further penetration as the knife slides through the
target.
Analysis of the indentation process shows that for slimmer indenters, as represented
by knives, frictional forces dominate, and indentation depth becomes dependent upon
the coefficient of friction between indenter and sample. Analytical models are
demonstrated to provide a reasonable estimate of energy absorption during and after
penetration for a wide variety of knives and armour materials. The key armour
parameters are shown to be the frictional interaction with the blade and the strength of
the target material. The performance of knife blades is shown to increase with
increasing sharpness, slimness, and surface finish. No single knife design performs
best against all types of armour, and no single armour is best against all knife blades.
