ISO 7539-6-2018 金属与合金的腐蚀--应力腐蚀测试--第6部分：恒定负荷或恒定位移条件下试验用预破裂试样的制备和使用 Corrosion of metals and alloys -- Stress corrosion testing -- Part 6: Preparation and use of precracked specimens for tests under constant load or constant displacement

This document specifies procedures for designing, preparing and using precracked specimens for investigating susceptibility to stress corrosion. It gives recommendations for the design, preparation and use of precracked specimens for investigating susceptibility to stress corrosion. Recommendations concerning notched specimens are given in Annex A.
The term “metal” as used in this document includes alloys.
Because of the need to confine plasticity at the crack tip, precracked specimens are not suitable for the evaluation of thin products, such as sheet or wire, and are generally used for thicker products including plate bar and forgings. They can also be used for parts joined by welding.
Precracked specimens can be loaded with equipment for application of a constant load or can incorporate a device to produce a constant displacement at the loading points. Tests conducted under increasing displacement or increasing load are dealt with in ISO 7539-9.
A particular advantage of precracked specimens is that they allow data to be acquired, from which critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. The latter data can be taken into account when monitoring parts containing defects during service.th edition 2018-08 Corrosion of metals and alloys — Stress corrosion testing — Part 6: Preparation and use of precracked specimens for tests under constant load or constant displacement Corrosion des métaux et alliages — Essais de corrosion sous contrainte — Partie？6:？Préparation？et？utilisation？des？éprouvettes？préfissurées？pour？ essais sous charge constante ou sous déplacement constant Reference number ISO 7539-6:2018(E) ？ ISO 20