Mechanics of Interfaces Within Biological and Biomimetic Materials
Author: Ahmad Khayer Dastjerdi Toroghi
Publisher:
Published: 2014
Total Pages:
ISBN-13:
DOWNLOAD EBOOK"Nature, through millions of years, has evolved mechanically superior materials which have recently become a rich source of inspiration. Virtually all hard biological materials are composites where stiff, elongated inclusions are bound together through a soft polymeric "glue". In some of these composites such as nacre and bone, the stiff component is a hard and stiff minerals (aragonite in nacre and hydroxyapatite in bone) forming mineral-polymer composite while for others, such as tendon and plant cell wall, a stiff and strong polymer (collagen in tendon and cellulose in plant cell wall) constitutes the inclusion part of the polymer-polymer composite. These building blocks are bonded by softer organic materials, and the overall properties of these natural materials are highly dependent on the properties of these "weaker" interfaces. While the mechanical properties and the role of inclusions are well studied and understood, there is far less work reported in literature on the mechanics and properties of weak biological interfaces, and their composition, structure and mechanics are poorly understood. In this study the mechanical properties of weak biological interfaces in mollusk nacre are measured and their mechanics of deformation and fracture is characterized. To this end, first, the fracture toughness of interfaces within three different types of nacre (namely top shell, pearl oyster, and red abalone) is, for the first time, determined through combing the result of chevron notch fracture test, micrographs obtained from scanning electron microscope, and linear elastic fracture mechanics concept. The results revealed that fracture toughness of polymeric interfaces within nacre is indeed extremely low, in the order of the toughness of the mineral inclusions. A novel experimental method called Rigid Double Cantilever Beam (RDCB) is developed to measure the fracture toughness of very soft polymeric and biological interfaces. The method not only determines the fracture toughness of interfaces but also yields their cohesive strength, extensibility and stiffness. The method is successfully implemented on three engineering adhesives, and their fracture toughness and cohesive law are reported. The RDCB test is also used to study the effect of substrate, and chemical treatment on the interfacial fracture toughness and cohesive properties of a biological adhesive fibrin network. An eight-chain based model is then proposed to elucidate the bell-shaped cohesive law of fibrin interfaces. The new method can be used to characterize the cohesive behavior of other important proteins such as bone osteopontin. Finally, an improved fracture mechanics based criterion is developed to predict the failure of biological and engineered staggered composites. The model captures the nonuniform distribution of shear stresses along the interfaces, and the resulting stress fields within the inclusions. The criterion can be applied for a wide array of material behavior at the interface and will lead to optimal designs for the interfaces, in order to harness the full potential of bio-inspired composites. " --