
449Shock Physics
So the time it takes the rarefaction to reach the front face is
∆t
U
==
=
8 359
0 120
.
]
mm
s
s
µ
µ
(16.116)
Then, the total time for the shock pulse is the time between impact and the rarefaction
wave reaching the interface or
t
shock
sss=+=0 155 0 120 0 275.[]. [] .[]µµµ
(16.117)
To determine the velocity at which the magnesium plate will rebound, let us look at
Figure 16.18.
We have the densities of both materials, we have the longitudinal sound speeds, we have
u
2f
, so we can nd u
3f
by solving the following equations simultaneously:
0
3
30 2
Mg Mg Mg Mg f
L
L3f
c
p
pc
=
−
→= −
(16.118)
0
3
30
Mg Bras
rass Brass
L
f