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We have started from the premise that fatigue crack growth is simply the permanent displacement
of atoms from the tip of a crack. From there it naturally follows that we must observe and measure
displacements in the vicinity of a crack at a scale and resolution that is appropriate to the phenomena that we
are dealing with and the analytical models that we wish to use. In this paper we describe our use of digital image
correlation to measure crack tip displacement fields of a growing fatigue crack, and provide a range of
experimental data for the use of other researchers.