Mitigating kinematic locking in the material point method

The material point method exhibits kinematic locking when traditional linear shape functions are used with a rectangular grid. The locking affects both the strain and the stress fields, which can lead to inaccurate results and nonphysical behavior. This paper presents a new anti-locking approach that mitigates the accumulation of fictitious strains and stresses, significantly improving the kinematic response and the quality of all field variables. The technique relies on the Hu–Washizu multi-field variational principle, with separate approximations for the volumetric and the deviatoric portions of the strain and stress fields. The proposed approach is validated using a series of benchmark examples from both solid and fluid mechanics, demonstrating the broad range of modeling possibilities within the MPM framework when combined with appropriate anti-locking techniques and algorithms.