Modelling of localisation and scale effect in thick-walled cylinders with gradient elastoplasticity

We model the progressive localisation of deformation which causes failure around thick-walled cylinders under external radial pressure. The study is based on a second-gradient elastoplastic model developed to regularise the ill-posedness caused by material strain-softening behaviour. The stress increment is related to both the strain increment and its Laplacian. The gradient terms introduce an internal length scale to the material allowing robust modelling of its post-peak behaviour. The numerical implementation is based on a C-1 finite element displacement formulation. Mesh insensitivity in terms of load-displacement and failure mechanism is demonstrated. The internal length in the constitutive equations enables modelling of the scale effect in thick-walled cylinders, according to which the load required to induce failure appears to be much larger for small holes than for large holes. (C) 2001 Elsevier Science Ltd. All rights reserved.