Determination of post-necking stress-strain relationship for zirconium low-oxidation based on actual cross-section measurements by DIC

摘要

Numerous equations have been proposed to describe the behavior of metal sheets under uniaxial tensile loading in the post-critical region. Here, the evolution of the cross-section is unknown and it is unclear which equation is most appropriate for which material. In this study, the evolution of the actual specimen cross-section is determined via digital image correlation (DIC); the data is then used to establish the post-necking stress-strain curve. Ultra-high-speed cameras were employed to capture the initiation of necking and fracture in zirconium low-oxidation (ZIRLO) sheets based on changes in the specimen cross-section. True stresses are calculated based on the actual cross-sectional area. The results indicate that the onset of local necking can be determined as the point at which the second derivative of the strain at different locations across the specimen cross-section diverge. The stress-strain data obtained by this rather direct method is considered more realistic than the data from conventional extrapolation method and is expected to be more appropriate in conjunction with a damage model.