Analysis of an Intermediate Rear Axle Shaft Failure

Abstract

Because it is not immediately obvious whether bending or torsion has been the major cause of failure both effects are considered independently [5,6]. Bending under static loading The total weight of the rear axle system is W=50 kg [0.9 kN] and is assumed to be evenly shared by the two rear wheels. The bending moment occurring along the shaft may simply be determined from taking the product of the wheel reaction force and the moment arm (from wheel centre to location of interest) (Figure 4). M = W/2 x (760-516) = 61 Nm As the shaft wheel hub diameter, d = 12.5 mm, so bending stress, 3 32 / M d σ = Π 3 2 32 61/ 0.0125 318 / x x MN m = Π = Torsion due to drive transmission In this case the main primer mover is the engine of the Motorcycle. The power rating, P = 13.42 kW with an output speed, N=5000 rpm (Figure 5). The maximum shaft driven speed=5000x16/40 (sprocket teeth ratio) = 2000 rpm. The maximum applied torque in the drive shaft, T 60 2 T P N = ÷ Π = 13420x60/(2000x2π) = 64 Nm Shear stress due to drive, τ 3 16 / T d τ = Π 3 2 16 64 / 0.0125 167 / x x MN m = Π = Results of Fatigue Tests of Steel Specimens Subjected to Combined Bending and Torsion [6]. Material fatigue strength Grade 40C8 IS: 1570-88 stainless steel grade is used for the shaft and the following material data is obtained from Appendix B of Ref 3 and stress concentration factor data also from Appendix C of Ref 3. Ultimate Tensile strength σ T =560-670 MN/m 2 Yield stress=320 MN/m 2 Stress concentration factor at end of keyway, 9. 1 = T K [shaft with radial hole chart d/D=4/12] Stress concentration factor at change of diameter, 4. 1 = T K [stepped diameter with fillet r/D=3/12] Discussion of Findings According to American Society of Mechanical Engineers code for the Design of transmission of shafts, the maximum permissible working stress in tension or compression may be taken as: a) 112 M Pa for shafts without allowance for keyway b) 84 M Pa for shafts with allowance for keyway The maximum permissible shear stress may be taken as: a) 56 M Pa for shafts without allowance for keyway Figure 2: Failed Shaft. Figure 3: Shaft in assembled condition. Figure 4: Schematic layout of the transmission system of the prototype. Figure 5: Shaft failure in combined loading.