Measurement of fatigue crack deformation on the macro- and micro-scale: Uniform and non-uniform loading

Abstract This paper describes the experimental measurement of near-tip displacement fields for a fatigue crack growing in a small compact-tension specimen. The specimen is pre-cracked conventionally, but then loaded in-situ in a scanning electron microscope. Digital image correlation is applied to the images collected and is analysed using an elastic model to produce stress intensity factor histories. A simple elastic/plastic model due to Pommier and Hamam is also applied, and the resulting behaviour is discussed. A single overload is applied to the specimen, and the effect of this on the elastic and elastic–plastic results is examined. The results are also compared to earlier work of a similar nature using a long-distance microscope, which gives an understanding of crack behaviour at a macroscopic length scale.