The mode I crack tip asymptotic response of a solid characterised by strain
gradient plasticity is investigated. It is found that elastic strains dominate
plastic strains near the crack tip, and thus the Cauchy stress and the strain
state are given asymptotically by the elastic K-field. This crack tip elastic
zone is embedded within an annular elasto-plastic zone. This feature is
predicted by both a crack tip asymptotic analysis and a finite element
computation. When small scale yielding applies, three distinct regimes exist:
an outer elastic K field, an intermediate elasto-plastic field, and an inner
elastic K field. The inner elastic core significantly influences the crack
opening profile. Crack tip plasticity is suppressed when the material length
scale ℓ of the gradient theory is on the order of the plastic zone size
estimation, as dictated by the remote stress intensity factor. A generalized
J-integral for strain gradient plasticity is stated and used to characterise
the asymptotic response ahead of a short crack. Finite element analysis of a
cracked three point bend specimen reveals that the crack tip elastic zone
persists in the presence of bulk plasticity and an outer J-field
