A Numerical Study on Global and Local Parameters Controlling Fracture in the Brittle‐ductile Transition Temperature Region

Abstract

In this report on fracture studies pertinent to the brittleductile transition region the predictive capability of a local fracture parameter, i.e. maximum tensile stress normal to the crack plane (=maximum principal stress), and of a global fracture parameter, i.e. the J-integral, are compared for SENB and CNT specimens fractured at -70°C. The influence of constraint is also investigated, both locally as defined by the ratios of mean (hydrostatic) stress and maximum principal stress to von Mises stress, and globally as defined by the factor m =J/(uy.CTOD). Results obtained indicate that stress fields in a varying constraint environment (i.e. varying both spatially and with extent of plastic deformation) are not uniquely characterized by J and require additional information on the amount of constraint. Fracture predictions based on maximum principal stress ahead of the crack tip exhibit far less scatter than those based on J, but further investigations are required on the geometry (in)dependence of this local parameter. NOMENCLATURECTOD, 6, = Crack Tip Opening Displacement J = J integral m =constraint factor [m = J/(o,.CTOD)]x, = critical material distance for cleavage fracture u = stress uf = cleavage fracture stress uy = material yield stress uyy = normal stress in y-direction, normal to crack plane An = crack growth (stable, fibrous)