Investigation of strain localization on marine structural steels: Uniaxial tests

Results of a series of uniaxial tests to investigate fracture initiation states of AH32 steel, a ship structural steel, are presented. Strains at fracture are obtained using digital image correlation analysis via DaVis LaVision software, and the corresponding states of stress are obtained via a plastic flow rule and a hardening relationship using the measured strains. The strain fields are calculated to the point of fracture initiation where the fracture initiation is defined as the condition when the first visible crack appears in the digital image of the test specimen. The software provides displacement and strain fields of the entire region and any specified sub-region of the imaged surface, which uses a so-called ‘geometric mask’. The strain values are mask-size dependent due to the local nature of deformation before fracture. Therefore, in the current study, strain fields are obtained for various mask sizes to investigate the effect of mask size on failure strain, i.e., strain localization phenomena, with the minimum mask size chosen at roughly the limit of the continuum scale (O (100 μm)). The evolution of the stress and strain fields as a function of loading is provided for different mask sizes. Moreover, comparison of the failure strain as mask sizes are decreased provides information on strain convergence. In this investigation, non-convergence behaviors are obtained for all experiments, as failure strain increased as the mask sizes are decreased.