It has been claimed that KIC values can be predicted using the initiation values of J or COD from specimens much smaller than those required for an ASTM-valid test. A review of the available experimental evidence suggests that this claim is justified only where the failure mode is microvoid coalescence. Where cleavage occurs geometry effects become much more significant, and can lead to a change in fracture mode between large and small specimens. In these circumstances, reliable KIC predictions cannot be made.
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