A generalized essentially non-hourglass total Lagrangian SPH solid dynamics

Abstract: In this paper, we tackle a persistent numerical instability within the total Lagrangian smoothed particle hydrodynamics (TLSPH) solid dynamics. Specifically, we address the hourglass modes that may grow and eventually deteriorate the reliability of simulation, particularly in the scenarios characterized by large deformations. We propose a generalized essentially non-hourglass formulation based on volumetric-deviatoric stress decomposition, offering a general solution for elasticity, plasticity, anisotropy, and other material models. Comparing the standard SPH formulation with the original non-nested Laplacian operator applied in our previous work \cite{wu2023essentially} to handle the hourglass issues in standard elasticity, we introduce a correction for the discretization of shear stress that relies on the discrepancy produced by a tracing-back prediction of the initial inter-particle direction from the current deformation gradient. The present formulation, when applied to standard elastic materials, is able to recover the original Laplacian operator. Due to the dimensionless nature of the correction, this formulation handles complex material models in a very straightforward way. Furthermore, a magnitude limiter is introduced to minimize the correction in domains where the discrepancy is less pronounced. The present formulation is validated, with a single set of modeling parameters, through a series of benchmark cases, confirming good stability and accuracy across elastic, plastic, and anisotropic materials. To showcase its potential, the formulation is employed to simulate a complex problem involving viscous plastic Oobleck material, contacts, and very large deformation.