1) What does it mean to conduct a fatigue test with R = -0.5?
2) If you have a material that is initially hard and strong, would you expect it to cyclically harden or soften? What would be a way of characterizing how strong it must be initially to make your answer more quantitative?
3) What is the typical effect of increasing mean stress on fatigue life?
4) Explain the significance of statistical scatter in fatigue life, especially how this may affect the use of S-N curves for engineering purposes.