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Biocomposites such as bone exhibit synergistic superior mechanical properties compared to its constituents, protein (collagen) and mineral (hydroxyapatite). The importance of properties of constituents at the submicron scale with regard to the toughness and strength of bone is investigated employing a discrete lattice model. The results show that matrix failure as opposed to platelet breakage provides better toughness to the bone. There is a fairly sudden increase in the toughness of bone when the strength of mineral platelet to that of protein crosses a particular critical value. These could provide clues to the preparation of ultra-tough artificial composites and the treatment of diseases related to fragility of bone. . Downloaded from www.worldscientific.com by NANYANG TECHNOLOGICAL UNIVERSITY on 08/25/15. For personal use only. J. Mech. Med. Biol. 2008.08:527-539. Downloaded from www.worldscientific.com by NANYANG TECHNOLOGICAL UNIVERSITY on 08/25/15. For personal use only.

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Previously, buckling behavior of several conical and spherical shells have been studied with great rigor. In this paper, snap through buckling behaviour for metallic dished shells under uniform external pressure is investigated. These shells are geometrically complex since it consists of a shallow conical frustum with a flat closed top. Such shells find many engineering applications, for instance as actuator elements in control components in cryogenic engines. Currently, no clear guidelines exist for design performance evaluation of such peculiar shells. This paper aims to establish a valid FE methodology for buckling and post buckling analysis of such shells using ABAQUS in tandem with experiments. A parametric study is carried out to understand the effect of geometrical parameters and imperfection sensitivity of these shells to snap-through buckling. Moreover, experiments were carried out using 3-D Digital Image Correlation(3D-DIC) for measuring whole-field deflection and strains. Numerical analysis was carried out, using generalized Eigen value analysis and non-linear analysis using modified-Riks technique with various material models, to correlate with the experimental observations. Non-linear elasto-plastic analysis with perfectly elastic-plastic material model agrees well with the experimental observations. Comparison of results from the numerical study indicates that material plasticity has a major effect on critical buckling pressure.