a) What are the three basic factors required to produce fatigue failure. [3 marks] b) Describe, with the use of the diagrams, the typical cyclic waveforms for R = -1, R = 0 and R = 0.8 and label the values for mean stress, stress range and stress amplitude. [6 marks] c) Draw a Goodman diagram, indicating both the Goodman line and Gerber parabola. How might such a diagram be used to describe safe operating conditions? [8 marks] d) Describe the process of crack initiation under low cycle fatigue conditions with the aid of diagrams. [8 marks]