Studies and Models of Fracture Processes in Graphite

Rose and Tucker applied their fracture model to Sleeve graphite, an extruded, medium-grain, pitchcoke nuclear graphite used for fuel sleeves in the UK AGR (see Chapter 13). The performance of the model was disappointing the predicted 

While some of the direct observations discussed above are not in total agreement 

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Several additional, non-microstructural, inputs are required for the fracture model (i) Particle critical stress intensity factor, KIc. Here, the value determined in a previous study (Klc = 0.285 MPa in )[3] was adopted for all four graphites studied. This value is significantly less than the bulk Klc of graphites (typically -0.8-1.2 MPa rn). However, as discussed in the previous section, when considering fracture occurring in volumes commensurate in size with the process zone a reduced value of Klc is appropriate (ii) the specimen volume, taken to be the stressed volume of the ASTM tensile test specimens specimen used to determine the tensile strength distributions and (iii) the specimen breadth, b, of a square section specimen. For cylindrical specimens, such as those used here, an equivalent breadth is calculated such that the specimen cross sectional area is identical, i.e.,... 

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