ASTM G39-99(R2021) pdf free download

ASTM G39-99(R2021) pdf free download.Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens
1. Scope
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 is 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 (see Note 1). Stress calculations by this practice are not applicable to plastically stressed specimens. N OTE 1—It is the nature of these practices 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). 2 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 speci- men holders must be built to accommodate the specimens. A double-beam modification of a four-point loaded 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 practices deal with this aspect, for example, Practices D1141, G30, G36, G44, G50, and G85. The experimenter is referred to ASTM Special Technical Publication 425 (2). 1.6 The bent-beam practice 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 practice apply only to the state ofstress existing before initiation of cracks. 1.7 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard. 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 appro- priate safety, health, and environmental practices and deter- mine the applicability of regulatory limitations prior to use. (For more specific safety hazard information see Section 7 and 12.1.) 1.9 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Terminology
3.1 Definitions ofTerms Specific to This Standard: 3.1.1 cracking time—the time elapsed from the inception of test until the appearance of cracking. 3.1.1.1 Discussion—The test begins when the stress is applied and the stressed specimen is exposed to the corrosive environment, whichever occurs later. 3.1.1.2 Discussion—The specimen is considered to have failed when cracks are detected. Presence of cracks can be determined with or without optical, mechanical, or electronic aids. However, for meaningful interpretation, comparisons should be made only among tests employing crack detection methods of equivalent sensitivity. 3.1.2 stress-corrosion cracking—a cracking process requir- ing the simultaneous action ofa corrodent and sustained tensile stress. This excludes corrosion-reduced sections that fail by fast fracture. It also excludes intercrystalline or transcrystalline corrosion which can disintegrate an alloy without either applied or residual stress.
4. Summary of Practice
4.1 This practice involves the quantitative stressing of a beam specimen by application of a bending stress. The applied stress is determined from the size of the specimen and the bending deflection. The stressed specimens then are exposed to the test environment and the time required for cracks to develop is determined. This cracking time is used as a measure of the stress-corrosion resistance of the material in the test environment at the stress level utilized.