It is commonly assumed in analysing fatigue data that there is a definite functional relationship between life in number of cycles and stress level. However, as has been pointed out several times (1, 2), an examination of the data shows considerable scatter. Even with carefully prepared smooth specimens, all from the same heat of steel, treated in the same manner and tested in the same laboratory, a range of 2 to 1 in number of cycles for failure at the same stress level is normal (1) and a range of 10 to 1 is not unusual (2). If the specimens are tested by different laboratories, slightly varying techniques will introduce further scatter (3).

This book provides a comprehensive guidance for the use of sound statistical methods and for the evaluation of fatigue data of welded components and structures obtained under constant amplitude loading and used to produce S-N curves. Recommendations for analyzing fatigue data are available, although they do not deal with all the statistical treatments that may be required to utilize fatigue test results, and none of them offers specific guidelines for analyzing fatigue data obtained from tests on welded specimens. For an easy use, working sheets are provided to assist in the proper statistical assessment of experimental fatigue data concerning practical problems giving the procedure and a numerical application as illustration.