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A device for in situ SEM examination of crack propagation during loading of compact tension specimens is described, with a specific demonstration on an alumina ceramic. The device facilitates direct qualitative observations of the inception and subsequent frictional pullout of grain‐localized bridges at the crack interface. Quantitative data on the bridging mechanism are obtained from measurements of the crack‐opening displacements behind the crack tip. The crack profile is found to be closer to linear than parabolic at the bridged interface. Deconvolution of these crack‐opening data allow for an evaluation of the closure tractions operative at the crack walls within the bridging zone, and thence the R ‐curve.
Rödel et al. (Thu,) studied this question.