Abstract
This paper introduces the use of digital image correlation for the measurement of surface displacements in the neighbourhood of a crack tip, both at the macro- and micro- scale. Various methods of interpreting the measured data and producing a crack driving force are then discussed, including the use of the full CJP model. A reduced set of parameters are then proposed, corresponding to the three principal interaction forces between the plastic enclave and the surrounding elastic material. Our own results, and those of Vasco Olmo, previously reported in the literature are then reanalysed using this new framework, and excellent agreement between two independent experiments is obtained. Implications for the analysis of further data sets are then discussed.
Highlights
U nderstanding the mechanics of fatigue crack propagation is important if we are to safely operate a wide range of engineering systems
This paper introduces the use of digital image correlation for the measurement of surface displacements in the neighbourhood of a crack tip, both at the macro- and micro- scale
The CJP model attempts to capture some of the additional phenomena generated by a fatigue crack with a plastic wake
Summary
U nderstanding the mechanics of fatigue crack propagation is important if we are to safely operate a wide range of engineering systems. Most of the methods are based on the Paris law relation between da/dN and delta K This ‘law’ is justifiably popular, it is in essence a simple empirical curve fit to laboratory data obtained at constant remote load amplitude. Our developing work at Oxford in the area described above has been presented previously at the Forni di Sopra [1], Malaga [2], and Urbino [3] IJ Fatigue/FFEMS workshops. It has employed digital image correlation on the macro and micro scale to measure and analyse near tip displacements fields. At Urbino [3], we reported measurements taken during in-situ loading of a fatigue crack in a scanning electron microscope (Fig.1.)
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