The present work uses a more accurate thermoelastic formulation than the classical equation, based on the inclusion of a higher order term, to analyze crack tip thermoelastic data. It is shown that this thermoelastic analysis (TSA) model can be fitted to the Christopher–James–Patterson crack tip field model and hence provides information on crack tip shielding. To validate the results of this analysis, stress intensity factors (SIFs) were compared with results obtained from digital image correlation (also fitted to the CJP model). A comparison was also made between these CJP‐derived SIF values and those obtained using a purely elastic Irwin–Westergaard approach. A high level of agreement was observed between DIC and TSA results in assessing ΔKCJP that is the net result of the driving and the shielding forces on the crack tip. The ability to assess shielding using TSA is a significant step forward in its potential use in a more accurate characterization of crack tip fields.

This paper describes a novel differential geometry method that is used in combination with 3D digital image correlation (3D-DIC) for crack tip field characterization on non-planar (curved) surfaces. The proposed approach allows any of the two-dimensional crack tip field models currently available in the literature to be extended to the analysis of a 3D developable surface with zero Gaussian curvature. The method was validated by analyzing the crack tip displacement fields on hollow thin-walled cylindrical specimens, manufactured from either 304L or 2024-T3 alloy that contained a central circumferential crack. The proposed approach was checked via a comparison between experimentally measured displacement fields (3D-DIC) and those reconstructed from a modified 2D crack tip model (utilizing either 2, 3, or 4 terms of the William's expansion series) and implementing a 3D geometrical correction. Further validation was provided by comparing model-derived stress intensity factors with values provided by empirical correlations.

A growing fatigue crack gives rise to a plastically deformed wake of material that envelops the crack. In this work, the plastic wake extent during fatigue crack growth is experimentally quantified by analyzing the crack tip displacement fields measured with digital image correlation. A novel technique based on use of a yield criterion is proposed that uses the undamaged state of the specimen as the reference state in the image processing. The plastic wake was identified by differentiation of the residual displacement fields obtained with a near-zero load level to avoid any rigid body motion. The plastic wake extent was then found by assuming that the boundary between the elastic and plastic regions would occur when the equivalent stress was higher than the yield stress of the material. The results presented can contribute to a better understanding of the mechanisms driving fatigue crack propagation.

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