Question

Hint: Use trial and error procedure to identify the critical crack length required for brittle fracture Integrate Paris law numerically to obtain number of cycles to failure Problem 3 (40 marks) The cross-section of a prototype gun barrel is shown in the figure below. Under repeatod firing, the barrel rapidly develops an array of 40 radial cracks, which undergo fatigue growth as a result of cyclic pressurization. It is a requirement that the fatigue life of the barrel, based on an initial crack length of 5 mm and firing pressure of 400 MPa, shall exoeed the predicted wear life of 10,000 rounds. Does the proposed barrel meet the specification? As a modification, it is proposed that the barrel be fully autofrettaged (a process in which high pressures are applied to the bore during manufacture in order to induce internal yielding, and hence an advantageous compressive stress ficld ncar the bore). What is the fatigue life of the modified barrel? A new round is proposed which would operate at a higher pressure. What is the maximum working pressure of the autofrettaged barrel which would meet the original life specification of 10,000 rounds? Comment on the effect of autofrettage on the fatigue life of the component. What effect does full autofrettage have on the fatigue growth rate of external radial cracks? (Material properties: Yield stress Y-1200 MPa, KK-90 MPamn, Paris' law m-3.1, C-L45S x 10-11, for crack growth in m/cycle). An approximate solution (error 109%) for the stress intensity factor for a peessurized thick cylinder with 40 radial cracks is provided for reference. Hint: Find a fit for Q(a/W) in Fig 2 using suitable software and proceed in the same way as Problem 2 50mm Pressure 100mm Fig I: Prototype pun herrel with multiple radial craciks emanating from the inner radius (Problem 3 up

Answer 1