The  stress space is shown as intersecting planes in Figure 6.7. The region inside this space is regarded as safe, whereas any point on or outside the intersecting planes will be an unsafe or a failure point. A safe state of stress with normal stresses alone is shown inside the envelope.
A fully 3D state of stress will represent an envelope or surface in six dimensional stress space.
           
The maximum stress theory for planar state of stress is given for normal stresses as

(6.4)

and for shear stress as

(6.5)

Now, consider that an off axis lamina is subjected to an axial stress of . Then, we can write the maximum stress theory for the planar state of stress for off axis lamina as follows.
           
Recalling the stress transformation for planar state of stress, we write the stress components in principal material directions as

(6.6)

Thus, the maximum stress theory for off-axis lamina loaded axially can be written as

Figure 6.7: Failure envelope for normal stress space with an example safe stress state inside the envelope

(6.7)