ASTM E399-22

5.1?The property 5.1.1?Variation in the value of K_Ic can be expected within the allowable range of specimen proportions, a/W and W/B. K_Ic may also be expected to rise with increasing ligament size. Notwithstanding these variations, however, K_Ic is believed to represent a lower limiting value of fracture toughness (for 2 % apparent crack extension) in the environment and at the speed and temperature of the test.

5.1.2?Lower values of K_Ic can be obtained for materials that fail by cleavage fracture; for example, ferritic steels in the ductile-to-brittle transition region or below, where the crack front length affects the measurement in a stochastic manner independent of crack front constraint. The present test method does not apply to such materials and the user is referred to Test Method E1921 and E1820. Likewise this test method does not apply to high toughness or high tearing-resistance materials whose failure is accompanied by appreciable amounts of plasticity. Guidance on testing elastic-plastic materials is given in Test Method E1820.

5.1.3?The value of K_Ic obtained by this test method may be used to estimate the relation between failure stress and crack size for a material in service wherein the conditions of high constraint described above would be expected. Background information concerning the basis for development of this test method in terms of linear elastic fracture mechanics may be found in Refs 5.1.4?Cyclic forces can cause crack extension at 5.1.5?Plane-strain fracture toughness testing is unusual in that there can be no advance assurance that a valid 5.1.6 Residual stresses can introduce bias into the indicated 5.2?This test method can serve the following purposes:

1.1?This test method covers the determination of fracture toughness (1.1.1?The K_Ic test procedure is described in the main body of this test standard and is a mandatory part of the testing and results reporting procedure for this test method. The 1.1.2?The K_Isi test procedure is described in Appendix X1 and is an optional part of this test method. The K_Isi test procedure is based on a fixed amount of crack extension of 0.5 mm, and as a result, Note 1:?Plane-strain fracture toughness tests of materials thinner than 1.6 mm (0.063 in.) that are sufficiently brittle (see 7.1) can be made using other types of specimens 1.2?This test method is divided into two parts. The first part gives general recommendations and requirements for testing and includes specific requirements for the K_Ic test procedure. The second part consists of Annexes that give specific information on displacement gage and loading fixture design, special requirements for individual specimen configurations, and detailed procedures for fatigue precracking. Additional annexes are provided that give specific procedures for beryllium and rapid-force testing, and the 1.3?General information and requirements common to all specimen configurations:

1.4?Specific requirements related to test apparatus:

1.5?Specific requirements related to individual specimen configurations:

1.6?Specific requirements related to special test procedures:

1.7?The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.8?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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9?This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.