On improved crack tip plastic zone estimates based on T-stress and on complete stress fields

Cracked ductile structures yield locally to form a plastic zone (pz) around their crack tips, which size and shape controls their structural behaviour. Classical pz estimates are based solely on stress intensity factors (SIF), but their precision is limited to very low sn/SY nominal stress to yield strength ratios. T-stresses are frequently used to correct SIF-based pz estimates, but both SIF and SIF plus T-stress pz estimates are based on truncated linear elastic (LE) stress fields that do not satisfy boundary conditions. Using Griffith's plate complete LE stress field to avoid such truncated pz estimates, the influence of its Williams series terms on pz estimation is evaluated, showing that T-stress improvements are limited to medium sn/SY values. Then, corrections are proposed to introduce equilibrium requirements into LE pz estimates. Finally, these improved estimates are compared with pz calculated numerically by an elasticplastic finite element analysis.