General Conclusions
Normal and shear stresses in the x and y directions can be determined by some means for a component.
At orientations other than the x and y directions, there are different combinations of normal stress and shear stress. The x and y stresses don't change — only our reference frame changes.
In one particular orientation, we find the largest normal stresses. These stresses are called principal stresses. On principal stress planes, there is no shear stress.
In another orientation, we find the maximum shear stress. This orientation is 45° away from the principal stress orientation. In general, both normal stress and shear stress act on the maximum shear stress planes.
