Modeling of interface strength as well as interface deformation based on nanomechanics and development of interface database systems

Tao Qu, Purdue University

Abstract

Biomaterials such as bone and marine exoskeletons have primarily an organic phase (e.g. tropocollagen in bone, chitin in exoskeleton) and an inorganic phase (e.g. hydroxyapatite in bone, calcite in exoskeleton) arranged in a precisely organized multi-level hierarchical arrangement. Interfacial interactions between the organic and inorganic phases significantly affect the mechanical properties of such biomaterials. In presented study, idealized tropocollagen-hydroxyapatite and chitin-calcite interfacial systems are analyzed using a multiscale simulation framework that combines explicit three-dimensional molecular dynamics simulations with finite element simulations that take into account explicit microstructure in a three-dimensional hierarchy. The analyses focus on the shear deformation that occurs in interfaces of such materials when overall three-dimensional hierarchy is subjected to mechanical loading. In order to predict the interface stress magnitude in such systems during deformation, steered molecular dynamics simulations are performed to study the interfacial sliding process between the organic and inorganic phases at the nanoscale. A visco-plastic interfacial sliding model is used to calculate the interface strength and the shear viscosity of each interfacial system. In order to predict the effect of interface on the behavior of the material at the continuum level, a combined extended finite element and cohesive zone model framework is used to predict the fracture properties of bio-inspired laminates with bio-interfaces as the adhesive layers. Analyses show that at the nanoscale, the presence of the interface with larger viscosity is the main contributor of the toughening mechanisms to prevent catastrophic failure, by enhancing the shear contribution in the overall mechanical behavior, affecting the stress distribution, and promoting energy dissipation required for viscoelastic deformation of the organic phases. At the laminate level, finite element analyses indicate that interface has significant effect on the delamination as well as the intra-laminar fracture resistance. Interface with higher critical fracture energy leads to higher delamination resistance, while influence on the intra-laminar fracture resistance is much more complicated which depends on the local stress state at the interface. Theoretical predictions for the energy release rate as a function of phase angles of mode mix based on the stress profile at the interface are derived to illustrate the interface effect. Further, the interface database system which correlates the mechanical properties of the bio-inspired laminated composites with structural morphology and interfacial stress is proposed. The database system is expected to guide the selection of interfaces to optimize the performance of laminated composites using the biomimetic strategies.

Degree

Ph.D.

Advisors

Tomar, Purdue University.

Subject Area

Mechanics

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