Shallow flaws under biaxial loading conditions - Part II: Application of aWeibull stress analysis of the cruciform bend specimen using a hydrostaticstress criterion

Cruciform beam fracture mechanics specimens have been developed in the Heav y Section Steel Technology Program at Oak Ridge National Laboratory to intr oduce a prototypic, far-field, out-of-plane biaxial bending stress componen t in the test section that approximates the nonlinear biaxial stresses resu lting from pressurized-thermal-shock ol pressure-temperature loading of a n uclear reactor pressure vessel (RPV). Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensio nal (constant-depth) shallow surface flaws. Tests were conducted under biax ial load ratios ranging from uniaxial to equibiaxial. These tests demonstra ted that biaxial loading can have a pronounced effect on shallow-flaw fract ure toughness in the lower transition temperature region for RPV materials. Two and three-parameter Weibull models have been calibrated using a new sc heme (developed at the University of Illinois) that maps toughness data fro m test specimens with distinctly different levels of crack-tip constraint t o a small-scale-yielding Weibull stress space. These models, with a new hyd rostatic stress criterion in place of the more commonly used maximum princi pal stress in the kernel of the Weibull stress integral definition, have be en shown to correlate the experimentally observed biaxial effect in crucifo rm specimens, thereby providing a scaling mechanism between uniaxial and bi axial lending states.