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BS EN ISO 7539-6:2018 pdf free

BS EN ISO 7539-6:2018 pdf free.Corrosion of metals and alloys – Stress corrosion testing
The use of precracked specimens acknowledges the difficulty of ensuring that crack-like defects introduced during either manufacture or subsequent service are totally absent from structures.Furthermore, the presence of such defects can cause a susceptibility to stress corrosion cracking which in some materials (e.g. titanium) may not be evident from tests under constant load on smooth specimens.The principles of linear elastic fracture mechanics can be used to quantify the stress situation existing at the crack tip in a precracked specimen or structure in terms of the plane strain-stress intensity.
The test involves subjecting a specimen in which a crack has been developed by fatigue from a machined notch to either a constant load or displacement at the loading points during exposure to a chemically aggressive environment. The objective is to quantify the conditions under which environmentally assisted crack extension can occur in terms of the threshold stress intensity for stress corrosion cracking, KIscc, and the kinetics of crack propagation.
The empirical data can be used for design or life prediction purposes, in order to ensure either that the stresses within large structures are insufficient to promote the initiation of environmentally assisted cracking, whatever pre-existing defects may be present, or that the amount of crack growth which would occur within the design life or inspection periods can be tolerated without the risk of unstable failure.
Stress corrosion cracking is influenced by both mechanical and electrochemical driving forces.The latter can vary with crack depth, opening or shape because of variations in crack-tip chemistry and electrode potential and may not be uniquely described by the fracture-mechanics stress intensity factor.
The mechanical driving force includes both applied and residual stresses. The possible influence of the latter shall be considered in both laboratory testing and the application to more complex geometries.Gradients in residual stress in a specimen may result in non-uniform crack growth along the crack front.BS EN ISO 7539-6 pdf free download.

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