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 E 399 is the basic test method to be used for plane-strain fracture toughness testing of aluminum alloys. The purpose of this practice is to provide supplementary information for plane-strain fracture toughness of aluminum alloys in three main areas: 1.2.1 Specimen sampling, 1.2.2 Specimen size selection, and 1.2.3 Interpretation of invalid test results. 1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are provided for information only. 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.