Songyun Ma

Continuum damage modeling and simulation of hierarchical dental enamel

Dental enamel exhibits high fracture toughness and stiffness due to a complex hierarchical and graded microstructure, optimally organized from nano- to macro-scale. In this study, a 3D representative volume element (RVE) model is adopted to study the deformation and damage behavior of the fibrous microstructure. A continuum damage mechanics model coupled to hyperelasticity is developed for modeling the initiation and evolution of damage in the mineral fibers as well as protein matrix. Moreover, debonding of the interface between mineral fiber and protein is captured by employing a cohesive zone model. The dependence of the failure mechanism on the aspect ratio of the mineral fibers is investigated. In addition, the effect of the interface strength on the damage behavior is studied with respect to geometric features of enamel. Further, the effect of an initial flaw on the overall mechanical properties is analyzed to understand the superior damage tolerance of dental enamel. The simulation results are validated by comparison to experimental data from micro-cantilever beam testing at two hierarchical levels. The transition of the failure mechanism at different hierarchical levels is also well reproduced in the simulations.

Anisotropic constitutive model incorporating multiple damage mechanisms for multiscale simulation of dental enamel

An anisotropic constitutive model is proposed in the framework of finite deformation to capture several damage mechanisms occurring in the microstructure of dental enamel, a hierarchical bio-composite. It provides the basis for a homogenization approach for an efficient multiscale (in this case: multiple hierarchy levels) investigation of the deformation and damage behavior. The influence of tension-compression asymmetry and fiber-matrix interaction on the nonlinear deformation behavior of dental enamel is studied by 3D micromechanical simulations under different loading conditions and fiber lengths. The complex deformation behavior and the characteristics and interaction of three damage mechanisms in the damage process of enamel are well captured. The proposed constitutive model incorporating anisotropic damage is applied to the first hierarchical level of dental enamel and validated by experimental results. The effect of the fiber orientation on the damage behavior and compressive strength is studied by comparing micro-pillar experiments of dental enamel at the first hierarchical level in multiple directions of fiber orientation. A very good agreement between computational and experimental results is found for the damage evolution process of dental enamel.

Multiscale Experimental and Computational Investigation of Nature’s Design Principle of Hierarchies in Dental Enamel

Dental enamel possesses extraordinary mechanical properties due to a complex hierarchical and graded microstructure. In this study, multiscale experimental and computational approaches are employed and combined to study nature’s design principle of the hierarchical structure of bovine enamel for developing bio-inspired advanced ceramics with hierarchical microstructure. Micro-cantilever beam tests are carried out to characterize the mechanical properties from nano- to meso-scale experimentally. In order to understand the relationship between the hierarchical structure and the flaw-tolerance behavior of enamel, a 3D representative volume element (RVE) is used in a numerical analysis to study the deformation and damage process at two hierarchical levels. A continuum damage mechanics model coupled to hyperelasticity is developed for modeling the initiation and evolution of damage in the mineral fibers as well as protein matrix. Moreover, debonding of the interface between mineral fiber and protein is captured by a cohesive zone model. The effect of an initial flaw on the overall mechanical properties is analyzed at different hierarchical levels to understand the superior damage tolerance of dental enamel. Based on the experimental and computational investigation, the role of hierarchical levels on the multiscale design of structure in dental enamel is revealed for optimizing bio-inspired composites.