Crack tip fields in ductile materials with martensitic phase transformation – A numerical 2D study

• Crack tip blunting in a TRIP-steel is simulated with finite elements.
• The impact of strain-induced phase transformation on mechanical fields is studied.
• A second maximum in opening stress and increased stresses and triaxiality are found.
• Implications for the fracture process are comprehensively discussed.
• Transformation toughening is explained for ductile failing TRIP-steels.

TRIP-steels show attractive mechanical properties attributed to martensitic phase transformation. The present work studies the influence of phase transformation on mechanical fields at stationary, blunting cracks. Finite deformation analysis of crack opening is done numerically utilizing a recently developed material model. The hardening effect of martensite formation causes increased stresses and triaxiality and a second maximum in opening stress ahead of the tip. Implications for fracture processes are discussed and beneficial effects of strain-induced phase transformation are concluded. A delayed crack propagation mechanism in the fracture process zone and shielding according to phase transformation around the process zone are implied.