A round stepped steel bar of diameters D and d with shoulder fillet r is subjected to axial tensile load P. Find the ratio between limit load PL and elastic limit load PY.
A. PL/PY = (D/d)^2
B. PL/PY = (D/d)^4
C. PL/PY = (D/d)^(-2)
D. PL/PY = (D/d)^(-4)