Multi-Scale Adhesion and Fracture: From Eco-friendly Structures to Biomedical Devices.

摘要

This thesis presents the results of a combined experimental, analytical and numerical study of fracture and adhesion in: sustainable building materials (bamboo and natural fiber-reinforced composites), restoration of a historical statue (Adam by Tullio Lombardo), and drug eluting stents. In each of these cases, multi-scale mechanism-based models were used to predict robustness.;In an effort to study the functionally graded bamboo structure, bamboo cross sections were examined using optical microscopy. This revealed the details of the functionally graded distribution of fiber bundles. Atomic Force Microscopy (AFM) was also used to characterize the microstructures of the molecular fiber bundles. Then, nano-indentation was used to measure the graded elastic moduli along with the radial direction. The measured elastic moduli were incorporated in finite element simulation of deformation and crack growth in resistance-curve experiments. The predictions from the models were in agreement with measured resistancecurves obtained for moso culm bamboo in the outside, inside and side orientations.;OPC-based cementitious fiber reinforced composites were fabricated using slurry vacuum method with carbonate filler, phyllite or metakaolin matrices and polypropylene or sisal fibers. Optical microscopy was used to study the in-situ fiber-bridging images obtained during three-point bend fracture/resistance-curve experiments. Single-fiber tensile tests were also used to measure the fiber tensile strengths. The measured fiber strengths were included in crack bridging models that were used to predict composite resistance-curve behavior. The predictions were in good agreement with the measured resistance curves.;Drug Eluting Stents (DES) are small drug coated scaffolds used to open the blocked arteries for patients with cardiovascular diseases. The CYPHER RTM stent is a multilayered structure with drug, parylene C and bare 316L steel layers. Based on prior AFM adhesion work, Brazil Nut experiments were performed to measure the interfacial fracture energy release rate for the interface of silane-parylene and bare 316L steel at various mode mixities. Interfacial fracture mechanics models were used to then link nano-scale AFM measurements of adhesives to microscale fracture mechanics measurement of interfacial fracture energies at different mode mixities.;Brazil Nut is used to study the subcritical crack growth rate in marble/adhesive interfaces. Four types of adhesives, Paraloid B72, Paraloid B48, a hybrid of B72/B48 and Epoxy, were selected to bond the Carrara marble Brazil Nut disks with fractured and smooth surfaces. Creep crack growth experiments were used to measure the dependence of energy release rates on crack growth rates between the Carrara marble and thermoplastic and thermosetting adhesives. The measured crack growth rates were incorporated into fracture mechanics predictions of service lives that were shown to be consistent with the lives of historical objects.