Structural basis for the fracture toughness of the shell of the conch Strombus gigas

Abstract

Natural composite materials are renowned for their mechanical strength and toughness: despite being highly mineralized, with the organic component constituting not more than a few per cent of the composite material, the fracture toughness exceeds that of single crystals of the pure mineral by two to three orders of magnitude. The judicious placement of the organic matrix, relative to the mineral phase, and the hierarchical structural architecture extending over several distinct length scales both play crucial roles in the mechanical response of natural composites to external loads. Here we use transmission electron microscopy studies and beam bending experiments to show that the resistance of the shell of the conch Strombus gigas to catastrophic fracture can be understood quantitatively by invoking two energy-dissipating mechanisms: multiple microcracking in the outer layers at low mechanical loads, and crack bridging in the shell's tougher middle layers at higher loads. Both mechanisms are intimately associated with the so-called crossed lamellar microarchitecture of the shell, which provides for 'channel' cracking in the outer layers and uncracked structural features that bridge crack surfaces, thereby significantly increasing the work of fracture, and hence the toughness, of the material. Despite a high mineral content of about 99% (by volume) of aragonite, the shell of Strombus gigas can thus be considered a 'ceramic plywood' and can guide the biomimetic design of tough, lightweight structures.

Structure and mechanical properties of selected protective systems in marine organisms

“…This growth has been shown to depend strongly on both nutrient availability and ambient environmental conditions [101]. At quasi-static loading rates in compression, the shells of abalone [66,97,102,103], conch [104,105] and giant clam [96] employ a variety of toughening mechanisms, realized through the brick-and-mortar structure of their nacre, including crack deflection and microbuckling of the calcium carbonate plates to induce a gradual "graceful failure." These toughening mechanisms are imaged in Fig.…”

A novel biomimetic approach to the design of high-performance ceramic–metal composites

“…These structural biological materials are sophisticated hierarchical composites based on brittle minerals and ductile polymers, which can exhibit mechanical properties that are far beyond those that can be achieved using the same synthetic compounds (Meyers et al 2008a). In particular, the principles of biologically controlled self-assembly in seashells have generated much recent interest (Jackson et al 1988;Kamat et al 2000;Evans et al 2001;Wang et al 2001;Rubner 2003;Mayer 2005); indeed, it has been suggested that their sophisticated structures can offer guidelines for the development of new generations of structural materials (Ortiz & Boyce 2008;Aizenberg & Fratzl 2009). …”

PREPARATION OF CALCIUM OXIDE FROM <i>Achatina fulica</i> AS CATALYST FOR PRODUCTION OF BIODIESEL FROM WASTE COOKING OIL

“…Achatina fulica (Indonesian; bekicot) is also containing CaCO 3 in the shell with high yield (88-99%) [15]. In Indonesia, the habitat of Achatina fulica usually is in banana tree and it is consumed with special name "crispy fried bekicot".…”