![]() ![]() These mechanisms can be exploited in materials design to retard crack growth via repair agents, residual stresses, phase transformations, plasticity-induced closure, crack deflection and crack bridging, etc. It is these micromechanisms that lie at the heart of the step-jumps in subcritical crack growth resistance achieved in new materials by tailored heterogeneity and interfaces at the micro- and nanoscales. However, it neglects the underlying competition between the intrinsic damage mechanisms occurring ahead of the crack and the extrinsic shielding mechanisms occurring behind the crack tip that influence fatigue behaviour. ![]() This global approach has served us very well, even in the case of relatively inhomogeneous materials, provided the crack is long relative to the scale of the heterogeneity. stress intensity factor K, crack-tip opening displacement (CTOD) J) that capture the local conditions at the crack tip, yet can be determined solely in terms of the crack length, externally applied loading and geometrical parameters. Finally, further opportunities for synchrotron X-ray microscopy are explored.Ĭonventional linear elastic fracture mechanics (LEFM) provides an established basis for analysing subcritical crack growth in terms of parameters (e.g. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. Conventionally, these are undertaken on separate synchrotron beamlines however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. ![]()
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