title: An over-nonlocal implicit gradient-enhanced damage-plastic model for trabecular bone under large compressive strains.
abstract: OBJECTIVE
  Investigation of trabecular bone strength and compaction is important for fracture risk prediction. At 1-2% compressive strain, trabecular bone undergoes strain softening, which may lead to numerical instabilities and mesh dependency in classical local damage-plastic models. The aim of this work is to improve our continuum damage-plastic model of bone by reducing the influence of finite element mesh size under large compression.
  
  
  METHODS
  This spurious numerical phenomenon may be circumvented by incorporating the nonlocal effect of cumulated plastic strain into the constitutive law. To this end, an over-nonlocal implicit gradient model of bone is developed and implemented into the finite element software ABAQUS using a user element subroutine. The ability of the model to detect the regions of bone failure is tested against experimental stepwise loading data of 16 human trabecular bone biopsies.
  
  
  RESULTS
  The numerical outcomes of the nonlocal model revealed reduction of finite element mesh dependency compared with the local damage-plastic model. Furthermore, it helped reduce the computational costs of large-strain compression simulations.
  
  
  CONCLUSIONS
  To the best of our knowledge, the proposed model is the first to predict the failure and densification of trabecular bone up to large compression independently of finite element mesh size. The current development enables the analysis of trabecular bone compaction as in osteoporotic fractures and implant migration, where large deformation of bone plays a key role.
authors.affiliation: Faculty of Medicine, Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstr. 78, Bern, CH-3014, Switzerland.
authors.forename: Hadi S
authors.initials: HS
authors.lastname: Hosseini
authors.affiliation: Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague, Zikova 1903/4, Praha 6, 166 36, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Horák
authors.affiliation: Faculty of Medicine, Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstr. 78, Bern, CH-3014, Switzerland.
authors.forename: Philippe K
authors.initials: PK
authors.lastname: Zysset
authors.affiliation: Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague, Zikova 1903/4, Praha 6, 166 36, Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Jirásek
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena / Q000502:physiology*; D001842:Bone and Bones / Q000502:physiology*; D019245:Compressive Strength / Q000502:physiology*; D050723:Fractures, Bone; D006801:Humans; D008954:Models, Biological
keywords: bone localization; densification; large deformation; nonlocal damage; softening