ASTM G39-99

1.1 This practice covers procedures for designing, preparing, and using bent-beam stress-corrosion specimens.

1.2 Different specimen configurations are given for use with different product forms, such as sheet or plate. This practice applicable to specimens of any metal that are stressed to levels less than the elastic limit of the material, and therefore the applied stress can be accurately calculated or measured (Note 1). Stress calculations by this practice are not applicable to plastically stressed specimens.

Note 1-It is the nature of these methods that only the applied stress can be calculated. Since stress-corrosion cracking is a function of the total stress, for critical applications and proper interpretation of results, the residual stress (before applying external stress) or the total elastic stress (after applying external stress) should be determined by appropriate nondestructive methods, such as X-ray diffraction (1).

1.3 Test procedures are given for stress-corrosion testing by exposure to gaseous and liquid environments.

1.4 The bent-beam test is best suited for flat product forms such as sheet, strip, and plate. For plate material the bent-beam specimen is more difficult to use, because more rugged specimen holders must be built to accommodate the specimens. A double-beam modification of a four-point specimen to utilize heavier materials is described in 10.5.

1.5 The exposure of specimens in a corrosive environment is treated only briefly, since other methods deal with this aspect, for example, Specification D1141, Practices G30, G36, G44, and G50, and Method G43. The experimenter is referred to ASTM Special Technical Publication 425 (2).

1.6 The bent-beam method generally constitutes a constant strain (deflection) test. Once cracking has initiated, the state of stress at the tip of the crack as well as in uncracked areas has changed, and therefore the known or calculated stress or strain values discussed in this method apply only to the state of stress existing before initiation of cracks.

1.7 The values stated in SI units are to be regarded as standard. The inch-pound equivalents in parentheses are provided for information.

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 and health practices and determine the applicability of regulatory limitations prior to use. (For more specific safety hazard information see Section 8 and 12.1.)