Abstract

The toughest engineering materials include stainless steels, and some high entropy alloys and nickel-based alloys. Their common denominator is a high strain hardening capacity. In this talk, we will elucidate the origins of this effect by combining micromechanics-based damage modelling and fracture testing. The experiments consist in determining the J integral at cracking initiation Jc, critical crack tip opening displacement dc, essential work of fracture, and degree of crack tip necking for different plate thicknesses. The modelling relies on an advanced non-local Gurson type model that is used to simulate crack growth in elastoplastic solids within a small-scale yielding framework as well as in real fracture mechanics specimens. As a first step, the impact of strain hardening on the plane strain toughness is addressed numerically. A high strain hardening capacity is connected to a significant reduction of the magnitude of the plastic strain at a fixed distance from the crack tip, hence delaying void growth and coalescence. 3D crack growth is then simulated and experimentally characterized in the near plane stress thin plate regime where the toughness of ductile metals heavily depends on thickness. This dependence is mainly related to the extra dissipation associated to crack tip necking which, itself, is very much dictated by strain hardening capacity. This study demonstrates that extreme levels of toughness can be attained by selecting the optimum thickness and a high strain-hardening capacity.