In an ballistic impact, for the same projectile with different velocities, how the damage area on the front face varies with impact velocity. Projectile is 9 mm FMJ with lead core and brass jacket with velocity range of 400 - 440 m/s. Target is Kevlar with the thickness of 5 - 10 mm.
In ballistic impacts a wide variety of projectiles, impact conditions and target materials occur. These lead to different failure mechanisms and hence damage zones (both in projectile and targets). Therefore, your question is too general to be answered.
It would help to specify the range in velocities, the type of projectile (material, mass and shape) and the type of target material/set up (materials, thicknesses).
Projectile is 9 mm FMJ with lead core and brass jacket with velocity range of 400 - 440 m/s. Target is Kevlar with the thickness of 5 - 10 mm.
Such a soft core bullet is easily stopped as it deforms ('mushrooms') upon impact on the Kevlar target. The increased diameter involves ever more primary fibers (that are in direct contact with the projectile) to be active, which reduces the stress per fiber and helps to avoid fiber breakage.
The fabric itself locally responses by out-of-plane deformation (frequently a pyramid or cone shape is formed). The size ('radius R') of this conical area growth radially, while the projectile velocity drops. Hence the cone shape changes from rather steep (initially) to a wide and low cone at a later stage. The conical area has the same velocity as that of the bullet and due to the increasing cone mass (linear with R^2), the kinetic energy of the projectile is now (mostly) converted into kinetic energy of the Kevlar.
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