REASONS FOR INTER–STATE RURAL TO URBAN MIGRATION IN DELHI (A Case Study based on 1981 and 1991 Census Data)

Fracture Behavior of Inhomogeneous Biological Materials and Interfaces   Biological materials like bone, nacre, human tooth layers are inhomogeneous materials made up of soft collagen, and hard, hydroxyapatite (HAP) mineral arranged in such a fashion so that these materials have higher strength and toughness, the measure of crack resisting behavior in materials, at the same time, which is exclusive in nature for different class of materials available for different application areas. The interfaces in these biological materials are designed in such a fashion so that the load transfer between the constituents takes place so smoothly, therefore, become a region of strength, not susceptible to failure like in other man-made materials and composites. It is important to understand these aspects of biological materials so that they can be mimicked to the novel materials to satisfy the growing need of different industries.   This work is focused on studying different layers of human tooth, and its interface for crack initiation and growth, the crack arresting behavior of the interface layer of the outer cover of human tooth, the enamel, and the inner, dentine, called dentine enamel junction. These works are done by developing a numerical model using the commercial finite element analysis tool, ABAQUS. The crack growth pattern of the enamel and the dentine has also been investigated. The role of porosity and permeability on the energy release rate which is the measure of fracture toughness has also been investigated. The key features of the book are:

• Study on the role of shear modulus of the defect and the matrix material in which the defect is embedded on the energy release rate.
• The role of small coating layer between the outer matrix and the inner layer on the fracture behavior, especially the stress concentrations in these different layers due to change in the elastic modulus.
• The crack growth pattern in human enamel, the outer tooth layer.
• The crack arresting phenomena of the interfacial, dentine enamel junction (DEJ).
• The role of porosity and permeability on the energy release rate in the inner layer of human tooth, dentine.

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