A General Strategy to Alleviate Volumetric Locking in 3D Finite Elements

  • Usta, Tolga (University of Stuttgart, Institute for Struct)
  • von Scheven, Malte (University of Stuttgart, Institute for Struct)
  • Bischoff, Manfred (University of Stuttgart, Institute for Struct)

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Three-dimensional finite elements are essential for the accurate representation of the complete stress state in solid mechanics. Nevertheless, nearly incompressible material behavior, such as rubber-like materials and metal plasticity, poses a persistent challenge due to volumetric locking. Over several decades, numerous techniques have been proposed to address this challenge. For eight-node hexahedral elements, one-point integration with hourglass control is a well-known and widely accepted method [1]. Despite its effectiveness, constructing a hexahedral-element-dominated mesh for complex structural geometries is difficult and, in many cases, impractical. In contrast, tetrahedral elements are well suited for meshing complex geometries and they are therefore often used in automatic meshing algorithms. Consequently, addressing volumetric locking within the tetrahedral element family is of particular importance. The standard four-node tetrahedral element with linear shape functions is fundamentally prone to volumetric locking due to its inherent geometrical constraints. The ten-node tetrahedral element with quadratic shape functions does not suffer from such geometrical constraints; however, volumetric locking can still occur, since the underlying cause is related to a material property, namely the bulk modulus. The method proposed in [2] splits the element stiffness matrix into constant and higher-order parts and removes volumetric locking by modifying the bulk modulus associated with the higher-order contributions, while preserving the constant part to ensure consistency. This method was later revisited and extended to an explicit time integration scheme in [3]. In this work, it is discussed how this method can be applied to plasticity. The particular challenge in this context is the fact, that the bulk modulus (or Poisson’s ratio, respectively) are not just material parameters that are accessible to direct manipulation. Instead, they depend on the flow rule. We gratefully acknowledge the support for this research from the DigiTain project (19S22006K), funded by the Federal Ministry of Economic Affairs and Energy (BMWE), following on a resolution of the German Bundestag.