Cavity expansion of a gradient-dependent solid cylinder

This paper presents an elasto-plastic analysis for cavity expansion in a solid cylinder. The solid is modelled using a strain gradient plasticity model to account for the influence of microstructures on the macroscopic mechanical behaviour. A numerical shooting method, together with Broyden’s iteration procedure, is developed to solve the resulting fourth-order ordinary differential equation with two-point boundary conditions for the gradient-dependent problem. Fully elastic-plastic solutions to the cavity expansion are obtained and they are compared with conventional results for a number of examples. The effects of microstructure on macroscopic behaviour for the cavity expansion problem are analysed. It is demonstrated that, with consideration of microstructural effects, the deformation and stress distributions in the cylinder are highly inhomogeneous during both the initial loading and the subsequent elastic and plastic expansion stages. The gradient effects can result in a stiffer response in the elastic regime (as compared with the corresponding conventional prediction), but a weaker response in the plastic regime. As expected, the overall elasto-plastic behaviour of the gradient- dependent cylinder depends on the material parameters as well as the cylinder thickness. It is shown that the strain gradient theory solutions reduce to the conventional ones as a special case when the dimension of the microstructures is negligible compared with the cylinder size. The results in this paper can be used as a benchmark for further numerical investigations of the cavity expansion problem.