Image-based analysis for crack propagation resistance in polygranular nuclear graphite

To enable monitoring of graphite that has been exposed to irradiated high-temperature environments, there is a need for analysis methods that are suitable for fracture toughness measurements in small test specimens. 

In this paper (Nuclear Materials and Energy), which is written entirely with results from the Part II undergraduate project of Dan Scotson (2019-2020) working in James Marrow's research group, fracture propagation has been studied for candidate graphites for next-generation nuclear energy.  Cracks were studied in the double-cleavage drilled-compression (DCDC) geometry with the surface full-field displacements measured by digital image correlation.

The measured crack displacement field was injected as boundary conditions into a finite element model, allowing the J-integral to be evaluated via the contour integral method, which then provides the mode 1 stress intensity factor during quasistatic crack propagation.

The analyais was validated using Macor, a linear elastic fine-grained glass ceramic with known fracture toughness.  The outlook for fracture testing of irradiated graphite at elevated temperatures is considered.