When is a notch a Crack? Analysis of an early paper by Rod Smith and Keith Miller

In 1978 Rod Smith published a paper, co-authored by Keith Miller, on the subject of notch fatigue limits. Of the many valuable contributions which Rod made to our field, this paper stands out for me. I believe it to be an excellent example of good science, bringing clarity to a field which was (and still is) characterized by complexity. In what follows I introduce the paper and in particular a type of plot used in it, which I propose to name the Smith-Miller diagram. This diagram is of great practical use in engineering design for the assessment of stress concentration features and also has applications in forensic failure analysis and in undergraduate teaching, areas in which Rod Smith also excelled.