IN MOST FRACTURE TOUGHNESS test standards, the validity of the results of the test, i.e., JQ, JQc, δQ, etc., would now be checked. Since the first fracture toughness standard (E 399), results could be considered nonvalid for two very different reasons. First, the data might not be of high enough quality: the crack front could be crooked, the precrack may not be of sufficient length, or the initial estimated crack length does not correspond to the result of the optical measurement. Second, the data were found not to satisfy the size requirements specified for the result to be considered, a KIc, a JIc, or whatever.