In recent years functionally-graded composites have been proposed to develop strong surfaces that can withstand high contact and frictional forces. The present work presents a new graded composite that can be used for the development of surfaces with excellent strength properties. The composite is inspired by the human teeth, which nature builds as a hard and tough functionally-graded composite. The outer surface of teeth is of enamel, composed of prismatic hydroxyapatite crystallites, whereas the inner part of teeth is of dentine, composed collagen fibrils and hydroxyapatite. Enamel is hard, brittle, and wear resistant, while dentine is softer and flexible. The dentine-enamel junction is formed as a region at which enamel mixes with dentine in a continuous way. The nanomechanical properties of the transition zone have been recently revealed. Of particular interest in this investigation is the variation in the elastic modulus from the pure enamel to the pure dentine material, which leads to biomimetic graded composites that exhibit high surface strength. This work presents analytical solutions for the stress and displacement fields on an actual composite substrate, which is loaded by a line load. The elastic modulus of the substrate follows approximately the theoretical distribution.

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