ASTM E1820-11e2

Assuming the presence of a preexisting, sharp, fatigue crack, the material fracture toughness values identified by this test method characterize its resistance to: (1) fracture of a stationary crack, (2) fracture after some stable tearing, (3) stable tearing onset, and (4) sustained stable tearing. This test method is particularly useful when the material response cannot be anticipated before the test. Application of procedures in Test Method E1921 is recommended for testing ferritic steels that undergo cleavage fracture in the ductile-to-brittle transition.

These fracture toughness values may serve as a basis for material comparison, selection, and quality assurance. Fracture toughness can be used to rank materials within a similar yield strength range.

These fracture toughness values may serve as a basis for structural flaw tolerance assessment. Awareness of differences that may exist between laboratory test and field conditions is required to make proper flaw tolerance assessment.

The following cautionary statements are based on some observations.

Particular care must be exercised in applying to structural flaw tolerance assessment the fracture toughness value associated with fracture after some stable tearing has occurred. This response is characteristic of ferritic steel in the transition regime. This response is especially sensitive to material inhomogeneity and to constraint variations that may be induced by planar geometry, thickness differences, mode of loading, and structural details.

The J-R curve from bend-type specimens recommended by this test method (SE(B), C(T), and DC(T)) has been observed to be conservative with respect to results from tensile loading configurations.

The values of δ_c, δ_u, J_c, and J_u may be affected by specimen dimensions.

1.1 This test method covers procedures and guidelines for the determination of fracture toughness of metallic materials using the following parameters: K, J, and CTOD (δ). Toughness can be measured in the R-curve format or as a point value. The fracture toughness determined in accordance with this test method is for the opening mode (Mode I) of loading.

1.2 The recommended specimens are single-edge bend, [SE(B)], compact, [C(T)], and disk-shaped compact, [DC(T)]. All specimens contain notches that are sharpened with fatigue cracks.

1.2.1 Specimen dimensional (size) requirements vary according to the fracture toughness analysis applied. The guidelines are established through consideration of material toughness, material flow strength, and the individual qualification requirements of the toughness value per values sought.

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

1.4 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.

Note 1—Other standard methods for the determination of fracture toughness using the parameters K, J, and CTOD are contained in Test Methods E399, E1290, and E1921. This test method was developed to provide a common method for determining all applicable toughness parameters from a single test.

A14.1.1 This annex covers the determination of the rate dependent J_Ic(t) and the J-integral versus crack growth resistance curve (J-R(t) curve) for metallic materials under conditions where the loading rate exceeds that allowed for conventional (static) testing, see Section 8.4.2.

A15.1.1 The normalization technique can be used in some cases to obtain a J-R curve directly from a force displacement record taken together with initial and final crack size measurements taken from the specimen fracture surface. Additional restrictions are applied (see A15.3) which limit the applicability of this method. The normalization technique is described more fully in Herrera and Landes (22) and Landes, et al. (23), Lee (24), and Joyce (21). The normalization technique is most valuable for cases where high loading rates are used, or where high temperatures or aggressive environments are being used. In these, and other situations, unloading compliance methods are impractical. The normalization method can be used for statically loaded specimens if the requirements of this section are met. The normalization method is not applicable for low toughness materials tested in large specimen sizes where large amounts of crack extension can occur without measurable plastic force line displacement.