Discuss how geometry, surface condition and material quality can have; a) A significant influence on the fatigue life of a cyclically stressed component. (5 marks) b) Explain the differences between crack propagation for ductile and brittle materials in respect to plastic flow at the crack tip (please illustrate using explanatory diagrams). (8 marks) c) A cylindrical welded liquid gas tank of minimum fracture toughness K1c = 55 MNm 3/2 (in the welded region) is subject to a twice daily refill that pressurises the tank. The internal pressure is restricted to a maximum of 40 bar. The minimum pressure when the tank is empty at the end of each day is 5 bar. During annual ultrasonic non-destructive testing a surface (edge) crack of length a = 3 mm is detected in the tank wall adjacent to the weld fusion zone. Assume that the tank is refilled twice per day 365 days per year. The tank has been in service for 10 years and has another 30 years left before it is scheduled to be replaced. Given that: Shape factor Y = 1.1, A= 2x10-2 m (MNm 3/2)- & m = 3 Tank wall thickness (t) = 10 mm Tank radius (R) = 1m&1 bar = 0.1 MPa Assess by appropriate calculation whether the tank is safe for the rest of its designated service life.