A contact and sliding interface algorithm for the combined particle-element method

This article presents a new contact and sliding interface algorithm for the Combined Particle-Element Method (CPEM) as applied to intense loading computations that include severe distortions. The CPEM is a recent development that allows for conversion of distorted elements into meshless particles. The advantages of this method are that the lower-strained particles (stress points) are computed with a fast and accurate finite-element formulation, and the higher-strained particles are computed with a meshless-particle formulation that can handle severe distortions. Furthermore, the meshless-particle algorithm, with Moving Least Squares (MLS) strain rates and Element-Free Galerkin (EFG) weak-form forces, is consistent and does not exhibit tensile instabilities. It is also well suited for conversion of finite elements into variable-connectivity meshless particles because the conversion does not require deletion of elements and addition of particles. Instead there is simply a branch point based on equivalent plastic strain. The basic approach can also be used for the element algorithm only or the particle algorithm only. Unfortunately, the CPEM has some characteristics that can introduce significant inaccuracies when used with existing contact/sliding algorithms. This article identifies and evaluates these issues, it provides a new and improved algorithm, and it demonstrates the capabilities and accuracy of the new algorithm with example computations.