Caveats on formulating finite elasto-plasticity in curvilinear coordinates

Abstract

Tensor analysis provides a frame-invariant foundation for continuum mechanics, yet numerical implementations rely on matrix representations expressed in user-selected bases. When these bases are non-Cartesian and non-orthonormal, additional terms arise that are normally absent or implicit in Cartesian formulations. Using cavity expansion as an initial model problem, this paper clarifies the roles of the deformation gradient, Jacobian, and shifter in finite-strain kinematics under axisymmetry. These quantities, typically straightforward in Cartesian frames, require more careful treatment in curvilinear coordinates, particularly in applications involving large deformations where axisymmetric reductions provide substantial computational savings. The formulation is further complicated when anelastic effects are included: the elastic and anelastic components of the deformation gradient and Jacobian must be distinguished, and the Cauchy stress depends on configuration changes beyond the current elastic state. This increases the complexity of the consistent linearisation required for finite element implementation. The paper provides a clear, step-by-step procedure for handling these contributions. The focus is practical rather than geometric. Instead of adopting a differential-geometric manifold framework, we work within standard Cartesian representations and use explicit changes of basis to obtain the required curvilinear forms. The resulting methodology enables robust finite element analysis of axisymmetric elasto-plastic problems undergoing finite strains.