For a beam of uniform strength, the bending stress (f) remains constant

throughout the beam length, even though the bending moment varies - this is

achieved by varying the depth (d) while keeping width (b) constant.

Bending stress relation: 

f M/Z (where Z = section modulus = bd²/6 (for rectangular section))

At the fixed end (x = L from free end), the bending moment is maximum:

M_max = WL

At this section, depth = d (maximum depth, occurring at the fixed end for a cantilever of

uniform strength since M = 0 at the free end, the theoretical depth there is zero).

Applying the bending equation at the fixed end: