Non-local plasticity effects on fracture toughness

The Mode I fracture strength in a nonlocal elastic-plastic material is analyzed under quasi-static steady crack growth. The plastic deformations are modelled using a constitutive model, where nonlocal plasticity effects are included in the instantaneous hardening moduli through a gradient measure of the effective plastic strain.

Fracture is modelled by a cohesive zone criterion. Results on the numerically obtained stress fields are presented, as well as results on the steady-state fracture toughness. It is shown that the nonlocal theory predicts lower steady-state fracture toughness compared to predictions by conventional J2-flow theory, since higher normal stresses in front of the crack tip are predicted.

Furthermore, the nonlocal material description increases the range of applicability of the cohesive zone model, since steady-state crack growth is possible for significantly larger values of the maximum stress in the traction-separation law normalised by the yield stress.