As shown in Figure P4, a circular shaft made of the 17-4 PH steel of Table P4 has a diameter of d = 60 mm and an initial crack length of ai = 0.5 mm. It is subjected to bending and is cycled between Mmin = 2 kN?m and Mmax = 14 kN?m. How many cycles are required to grow the crack to failure by brittle fracture?

Problem 4 As shown in Figure P4, a circular shaft made of the 17-4 PH steel of Table P4 has a diameter of d = 60 mm and an initial crack length of a; = 0.5 mm. It is subjected to bending and is cycled between Mmin = 2 kNm and Mmax = 14 kNm. How many cycles are required to grow the crack to failure by brittle fracture? P M K = FS SS (tension, P) S = S (bending, M) St Sb F for small a Limits for 10% on F 4P 32M a 0.728 < 0.2 or 0.35 d Note: 'Different limits for tension or bending, respectively. Figure P4 Table P4 Constants for the Walker Equation Yield Toughness Walker Equation Material 00 KIC Co Co m MPa MPa m mm/cycle in/cycle (ksi) (ksiin) (MPam)" (ksivin)" (R 0) (R < 0) 17-4 PH steel 1059 120 3.29 x 10-8 1.63 x 10-9 2.44 0.790 (154) (109)