1.1 This practice is applicable to the fracture toughness testing of all aluminum alloys, tempers, and products especially in cases where the tests are being made to establish whether or not individual lots meet the requirements of specifications and should be released to customers. 1.2 Test Method E399 is the basic standard test method for plane-strain fracture toughness testing of aluminum alloys. This practice augments Test Method E399 in three main areas: 1.2.1 Specimen size selection, 1.2.2 Fatigue cracking requirements, and 1.2.3 Interpretation of results of invalid tests. 1.2.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.