ASTM B909-21

4.1?The property 4.1.1?Thermal quenching processes used with precipitation hardened aluminum alloy products can introduce significant residual stresses into the product.5 Mechanical stress relief procedures (stretching, compression) are commonly used to relieve these residual stresses in products with simple shapes. However, in the case of mill products with thick cross-sections (for example, heavy gauge plate or large hand forgings) or complex shapes (for example, closed die forgings, complex open die forgings, stepped extrusions, castings), complete mechanical stress relief is not always possible. In other instances residual stresses may be unintentionally introduced into a product during fabrication operations such as straightening, forming, or welding operations.

4.1.2?Specimens taken from such products that contain residual stress will likewise themselves contain residual stress. While the act of specimen extraction in itself partially relieves and redistributes the pattern of original stress, the remaining magnitude can still be appreciable enough to cause significant error in the test result.

4.1.3?Residual stress is a non-proportional internal stress that is superimposed on the applied stress and results in an actual crack-tip stress-intensity factor that is different from one based solely on externally applied forces or displacements, and residual stress can bias the toughness measurement. Conceptually, compressive residual stress in the region of the crack tip must be overcome by the applied force before the crack tip experiences tensile stresses, thus biasing the 4.1.4?Tests that utilize deep edge-notched specimens such as the compact tension C(T) are particularly sensitive to distortion during specimen machining when substantial residual stress is present. In general, for those cases where such residual stresses are thermal quench induced, the resulting 4.2?This guide can serve the following purposes:

1.1?This guide covers supplementary guidelines for plane-strain fracture toughness testing of aluminum products for which complete stress relief is not practicable. Guidelines for recognizing when residual stresses may be significantly biasing test results are presented, as well as methods for minimizing the effects of residual stress during testing. This guide also provides guidelines for an empirical correction as well as interpretation of data produced during the testing of these products. Test Method E399 is the standard test method to be used for plane-strain fracture toughness testing of aluminum alloys.

1.2?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.

1.3?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.