
116 Ballistics: Theory and Design of Guns and Ammunition
We set this constant equal to
or 6K
2
. Here σ
Y
is the yield stress in simple tension and K
is the yield stress in pure shear. This implies that
σ
Y
K=
(4.22)
or
K
=
=
2
1 155
.
(4.23)
σ
Y
is also known as the equivalent stress and either σ
Y
or K can be found experimentally.
In σ
1
–σ
2
–σ
3
space, the criterion is represented by an ellipsoidal surface whose inner region
symbolizes stress states that are safe (nondistorting). This is shown two dimensionally in
Figure 4.3.
The Tresca or maximum shear stress criterion is used when the material is known to
have great ductility. It ...