Christine is correct on point 1. above.
The first change dates back to the Second World War with the publication of Code Case 979, which permitted a reduction in the design factor on tensile strength from 5 to 4, provided additional requirements were met. This was primarily motivated by the...
A very useful reference is Hales, R., Holdsworth, R., O'Donnell, M.P., Perrin, I.J., and Skelton, R.P., "A Code of Practice for Determination of Cyclic Stress-Strain Data", Materials at High Temperatures 19(4), pp. 165-185, 2002.
For an introductory overview of this topic, you should probably...
