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case of
σ
Y
= 1500
MPa (
L
= 540
mm vs.
L
= 510
mm, Fig. 3). It is clear
that this “singular” effect found during the numerical computations needs
physical explanation. This explanation can be done in terms of energy.
It is known that a volume of the cavity, which is formed in the target
during the high-velocity penetration of the projectile, depends on its kinetic
energy [19]. As it can be seen in Fig. 2, with the increase of the projectile
material yield strength at a fixed velocity there is a certain decrease of
the cavity lateral size (it evidently occurs due to some difficulties in the
projectile material spreading in the lateral direction on the contact boundary
with the target because of the strength forces). Decrease of the cavity
lateral size under the condition of a fixed volume must lead to increase
of the penetration depth. This fact seems to explain the initial increase
of
L
along with the increase of the projectile material yield strength. The
stronger projectile deforms less in the radial direction, which results in
spending less energy for radial expansion of the cavity. Further decrease
of the penetration depth along with the increase of the projectile material
strength can be connected with the increase of the energy spent on the
plastic deformation of the projectile itself.
It must be noted that the elongated projectile penetration model didn’t
account for the situation of possible destruction of both the projectile and
target materials which can happen under the real conditions. However,
this fact appears to have insignificant impact on the projectile penetration
dependence on the projectile material strength. The destruction cannot
immediately occur in the penetration area (in the projectile and target
material contact area of a radial size, which corresponds to the projectile
radius) since the materials are in the state of uniform compression in
this area. Destruction may appear (and experimental data prove it) when
the projectile material spreading over the penetration area in the radial
direction takes the form of a thin film and its intensive plastic deformation
almost stops. This film composition (whether it remains continuous or
undergoes destruction) is of little significance considering its impact on the
penetration.
Summing everything up it should be noted that the real values of
σ
Y
for the the VNZh-90 alloy (at the level of 1000MPa) are close to optimal
which provide the maximal penetration depth (see Fig. 3).
As it can be seen in Fig. 3, the projectile velocity has an impact on the
penetration depth that is more significant than on the projectile material
strength. The velocity of a projectile made of the VNZh-90 alloy with the
yield strength of 1000 MPa increases from 1400 to 2000 m/s, which results
in 12 mm cavity depth increase (from
L
= 545
mm to
L
= 670
mm);
it is approximately 23%. As the velocity increases, a cavity lateral size
increases considerably as well.
ISSN 0236-3941. HERALD of the BMSTU Series “Mechanical Engineering”. 2015. No. 1 75