Hamza S
The aim of the present review is to present some phenomenological observations on compression fatigue crack propagation of nacre samples. The first part of the paper reviews the characteristics of hierarchical structure and the mechanical properties of nacre, which characterize its specific properties. We have investigated the main chemical constituents of nacre and determined their mineral elements. Electron microscopy studies revealed that nacre is composed of a single-crystal aragonite. In the second part of the paper samples of nacre have been tested in compression-compression fatigue under cyclic loading and a Paris curve have been constructed at a fatigue ratio of about 10, subjected to a 30 Hz sinusoidal compressive load. It has been demonstrated that two driving forces ΔK and Kmax mainly govern the overall fatigue crack growth of nacre. Nacre shows considerable ability to stop cracking. By means of axial compression tests, we identified a single elastic and inelastic property. Measurements based on experiments were first done. Mean values of compressive strength and modulus of elasticity were obtained for several samples. A three-point bending test was performed on polished nacre samples according to the international standards for Young’s modulus, bending strength. An attempt is made to explain qualitatively the mechanical behavior of nacre in terms of its submicroscopic structure. It is concluded that the precise geometric arrangement of the plates is highly important. The results obtained provide a director for the design of orthopedic implants.
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