CONICET | Buscador de Institutos y Recursos Humanos

The Weibull stress has been accepted as a fracture criterion for cleavage fracture of steels and it has been used for the analysis of fracture toughness. However, the effect of temperature and/or the yielding scale on the critical Weibull stress has not yet been clarified. In the present work, the dependence of the critical Weibull stress on temperature and constraint was investigated on a low carbon steel. Weibull parameters of the critical Weibull stress were statistically evaluated with various notched round bar tensile specimens. Three test temperatures of -196oC, -130oC and -100oC were selected at which fully cleavage fracture surfaces could be obtained. The locations of the triggering points for cleavage in all fractured specimens were quantified by SEM observation. Local stress and strain conditions at the triggering points were also estimated by means of both the FE solutions and the triggering points. The local stress at those points shows the dependence on the local strain. In the original formulation of the Weibull stress proposed by Beremin, an important number of nucleated micro-cracks are assumed and the fracture probability from micro-crack is mainly defined by only the maximum principal stress. However, the present test results suggest that the straining history for the micro-crack nucleation should also be considered for the cleavage fracture criterion.