Loading Conditions Effects on Fatigue Life of Notched Rods Using Four-Point Bending Test

Shaft design assumes that the end supports of the shaft are simply supported that is not entirely correct. This article investigates the effects of simply supported ends and fixed-fixed supported ends on the bending moment developed in shafts. The bending moments and hence bending stress are life limiting parameters of shafts. Moreover, the effects of transverse loading inclination, loading spacing, and loading variation on the bending moment developed in shafts are studied. Analytical, numerical, and experimental approaches were adopted. Notched steel rods were used in fatigue experiments. The fatigue lives of those rods were measured and recorded. The bending moment applied to the rod specimen was calculated and compared to those obtained from the analytical and numerical approaches. The studies revealed that the simply supported end conditions will result in a shaft diameter that is 88% larger. However, the fixed-fixed end condition will result in a shaft diameter that is 67% smaller. The average bending moments of the simply supported and the fixed-fixed end conditions will result in the most accurate shaft diameter. Moreover, the maximum bending moment occurred when the load inclination angle θ = 0.0. It also increased with increasing the load ratio P₁/P₂ and the load spacing ratio l₁/L, where P₁, P₂, l₁, and L are respectively the left-hand load, the right-hand load, the position of P₁ from the left-hand support, and the total length of the shaft.