In situ analysis of crack fields and crack propagation

The fatigue and fracture properties of engineering materials are usually measured using standard test specimens.  However, real cracks in engineering structures are three-dimensional and more complex. Predicting whether and how quickly a crack will propagate with confidence and without excessive conservatism remains difficult. We aim to improve our understanding of crack propagation by investigating how the applied loading is mediated by the processes that occur around the crack. In other words, what are the local conditions that exist at the crack tip that allow it to propagate. These can be quite different from what we might expect if we only consider the remotely applied boundary conditions, which are the loads or displacements and crack geometry (length and shape).

One way to address this is to simultaneously examine both the strain and stress fields that exist when the crack propagates. This can be done by 2D and 3D digital correlation image analysis to obtain precise, in-situ, measurements of the material displacements at the surface and inside solid samples, and also measurements of the deformations of the crystal lattice by scattering of X-rays, neutrons or electrons. These measurements are used with numerical modelling to investigate the criteria for crack propagation. Some recent examples include nuclear graphite ( and, fatigue cracks in metals ( and and cleavage cracks in ceramics ( A requirement of this approach is the relationship between stress and strain. This can be non-linear and affected by damage, so its study is also necessary.

Several projects are available with the objective of developing novel methods to better characterise and understand the interaction between events at the crack tip and the surrounding deformation fields in structural materials. The projects will use experimental techniques that include SEM, XRD (synchrotron), Raman, optical and X-ray tomography and finite element modelling to study the propagation of cracks (brittle fracture, stress corrosion and fatigue).  The projects are suitable for graduates with an engineering, mathematical or physics background.

Strain mapping of a crack in graphite using synchrotron X-ray diffraction

Strain mapping of a crack in graphite using synchrotron X-ray diffraction (


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