
474 Ballistics: Theory and Design of Guns and Ammunition
is reected from the free surface with a net maximum tensile stress σ
T
, which will always
occur at the leading edge of the wave (Figure 16.34).
At any time, we can write
(16.228)
where σ
I
is the part of the compression wave remaining at an instant in time. If σ
T
ever
exceeds σ
F
, a fracture will occur. Thus at fracture, we can write
(16.229)
If we assume that this occurs at some instant, we will generate a spall thickness t
1
and we
can write this spall thickness as
λ
λ
−
=
(16.230)
c
c
c
c
t =
4
1
c
=
2
1
c
t =
t
< 0
t
= 0
σ
T
=
–σ
m
σ
T
=
–σ
m
c
c
+σ
m
+σ
m
σ
m
2
σ
1
=
+σ
m
–σ
–σ
m
–σ
m