Final answer:
The statement is false because shear stress reaches a maximum on planes where shear forces act, unlike planes with maximum normal stress, where shear stress is zero.
Step-by-step explanation:
Shear stress is related to the forces that act parallel to the surface of a material, causing layers within the material to slide past each other. This is different than normal stress, which is related to forces that act perpendicular to the surface, either stretching (tensile) or compressing (compressive) the material. Since shear stress is a result of forces acting parallel to a plane, it reaches a maximum on planes where there is shear and zero on planes where normal stresses are maximal. Therefore, the statement 'Shear stress is always maximum on the planes of maximum or minimum normal stress' is false. This is because the maximum normal stress occurs on planes where no shear force is acting, thus shear stress is zero.