The shear stress along the principal plane subjected to the maximum principal stress is zero.

Explanation:
- When a material is subjected to external forces, it experiences stresses in different directions. These stresses can be decomposed into normal and shear stresses.
- The principal stresses are the maximum and minimum normal stresses experienced by a material at a particular point.
- The principal planes are the planes on which the principal stresses act. These planes are perpendicular to each other.
- The maximum principal stress is the highest normal stress experienced by the material, and it occurs on the principal plane with the highest normal stress value.
- The minimum principal stress is the lowest normal stress experienced by the material, and it occurs on the principal plane with the lowest normal stress value.
- Shear stress occurs when forces are applied parallel to a plane, causing one part of the material to slide over the adjacent part. It is perpendicular to the normal stress.
- Along the principal planes, the shear stress is zero. This is because the principal planes are oriented in such a way that the maximum and minimum normal stresses act purely in the normal direction and do not cause any shearing motion.
- The shear stress can be calculated using the formula: shear stress = (maximum principal stress - minimum principal stress) / 2. Since the minimum principal stress is zero on the principal plane subjected to the maximum principal stress, the shear stress is also zero.

In conclusion, the shear stress along the principal plane subjected to the maximum principal stress is zero.

Since as per definition of Principal plane & as per Mohr's circle rule, Shear stress along Principal plane is Zero.