A coupled Eulerian-Lagrangian extended finite element formulation for simulating large deformations in hyperelastic media with moving free boundaries

We present a coupled Eulerian-Lagrangian (CEL) formulation aimed at modeling the moving interface of hyperelastic materials undergoing large to extreme deformations. This formulation is based on an Eulerian description of kinematics of deformable bodies together with an updated Lagrangian formulation for the transport of the deformation gradient tensor. The extended finite element method (XFEM) is used to discretize the mechanical equilibrium and deformation gradient transport equations in a two-phase domain. A mixed interpolation scheme (biquadratic for the velocity and bilinear for the deformation gradient) is adopted to improve the accuracy of the numerical formulation. The interface describing the deformed shape of the body is represented by the level set function and is evolved using the grid based particle method. The performance of the scheme is explored in two-dimensions in the compressible regime. For an adequate spatial and temporal discretization, our numerical results are in good agreement with theory and with numerical results from the traditional Lagrangian formulation (in Abaqus). The advantage of the proposed formulation is that material motion is not coupled with that of the mesh; this eliminates the issues of mesh distortion and the need for remeshing associated with Lagrangian formulations when bodies undergo very large distortions. It is therefore well adapted to describe the motion of complex fluids and soft matter whose physical properties are intermediate between conventional liquids and solids.