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- Biomechanics and Modeling in Mechanobiology
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- National Science Foundation
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Anisotropy and Heterogeneity in Finite Element Models of Trabecular Bone Alters Expected Failure OutcomesAt the nanoscale bone is composed of aligned mineralized collagen fibrils organized into packets along the surface of trabecular bone creating an anisotropic tissue microstructure. Newer packets at the trabecular surfaces are usually less mineralized than older bone in the interior of the trabeculae, which along with irregular mineral deposition within packets, forms a heterogeneous material across the span of a trabeculae. However, finite element (FE) models of bone typically use homogenous isotropic material properties, because it is challenging to build anisotropy and heterogeneity into a model in a way that is applicable to the complex geometries of trabecular bone. Both the material anisotropy and heterogeneity may influence the stress state of trabecular bone, and it is important to understand the implications of such differences for determining bone biomechanical failure. It was hypothesized that taking into consideration both the tissue anisotropy and heterogeneity of bone’s biomechanical properties would alter the expected failure locations by reducing tensile stress on near surface elements of an FE model of canine trabecular bone. The objective of this study was to test this hypothesis and to develop a method to apply anisotropic and heterogeneous material properties to a model automatically from micro-computed tomography (μCT) data.
Finite element modeling of meniscal tears using continuum damage mechanics and digital image correlation
Meniscal tears are a common, painful, and debilitating knee injury with limited treatment options. Computational models that predict meniscal tears may help advance injury prevention and repair, but first these models must be validated using experimental data. Here we simulated meniscal tears with finite element analysis using continuum damage mechanics (CDM) in a transversely isotropic hyperelastic material. Finite element models were built to recreate the coupon geometry and loading conditions of forty uniaxial tensile experiments of human meniscus that were pulled to failure either parallel or perpendicular to the preferred fiber orientation. Two damage criteria were evaluated for all experiments: von Mises stress and maximum normal Lagrange strain. After we successfully fit all models to experimental force–displacement curves (grip-to-grip), we compared model predicted strains in the tear region at ultimate tensile strength to the strains measured experimentally with digital image correlation (DIC). In general, the damage models underpredicted the strains measured in the tear region, but models using von Mises stress damage criterion had better overall predictions and more accurately simulated experimental tear patterns. For the first time, this study has used DIC to expose strengths and weaknesses of using CDM to model failure behavior in soft fibrous tissue.
This publication contains a finite element model for the analysis of single bone trabeculae under consideration of bone tissue heterogeneity and tissue anisotropy. The model for bone tissue heterogeneity and anisotropy follows: Hammond, M.A., Wallace, J.M., Allen, M.R. and Siegmund, T., 2018. Incorporating tissue anisotropy and heterogeneity in finite element models of trabecular bone altered predicted local stress distributions. Biomechanics and Modeling in Mechanobiology, 17(2), pp.605-614. In this publication the finite element model, material set assignment and local orientations are provided. This dataset contains an inp file in the syntax of Abaqus/Standard software v2017.
This publication contains a finite element model for the analysis of bone core under consideration of bone tissue heterogeneity and tissue anisotropy. The model for bone tissue heterogeneity and anisotropy follows: Hammond, M.A., Wallace, J.M., Allen, M.R. and Siegmund, T., 2018. Incorporating tissue anisotropy and heterogeneity in finite element models of trabecular bone altered predicted local stress distributions. Biomechanics and Modeling in Mechanobiology, 17(2), pp.605-614. In this publication the finite element model, material set assignment and local orientations are provided. This dataset contains an inp file in the syntax of Abaqus/Standard software v2017.
EFFECT OF MATRIX VISCOELASTICITY ON PREDICTION OF RESIDUAL STRESSES IN ORTHOGONAL 3D WOVEN COMPOSITESIn this paper, the effect of matrix viscoelasticity on the development of residual stresses in 3D woven composites is investigated using Finite Element Analysis. Based on experimental observations, it is hypothesized, that the stresses develop mainly due to the difference in the coefficients of thermal expansion between the fiber reinforcement and the matrix. The model considered is a “1x1 orthogonal” 3D woven composite unit cell that is generated using x-ray computed microtomography data. In this study, cooling after curing is considered under the assumption of zero stress at the beginning of the cooling. In addition to the full time- and temperature-dependent viscoelastic formulation, the applicability of two simplified constitutive methods, elastic and variable time pseudoviscoelastic, is investigated. It is observed that the pseudo-viscoelastic method predicts similar cumulative stress distribution (Von Mises and Hydrostatic) compared to the full viscoelastic results. The elastic model presented the highest stress values while the full viscoelastic model presented the lowest stress values.