The Role of the Organic Component in the Mechanical Behavior of Biomineralized Composites

Abstract

The roles of minor organic layers in influencing the mechanical response of such biomineralized composites as mollusk shells and sponge spicules have been investigated. The mechanisms whereby such minor constituents govern energy dissipation in rigid biomineralized structures are discussed, and a rationale for new modes of toughening that may relate more generally to families of ceramic- or glass/organic composites is offered. New results of simple torsional tests conducted on spicule fibers of a hexactinellid sponge, Euplectella aspergillum (Euplectella a.), compared with those done on melt-drawn glass fibers, showed an enhanced ability to resist failure in torsion, whereas the glass fibers did not. This behavior was attributed to the presence of a very thin adhesive viscoelastic phase between the siliceous layers of the spicule fibers, combined with the architectural and surface features of the spicule fiber.

New toughening concepts for ceramic composites from rigid natural materials

“…We have observed those differences qualitatively in the failure modes of sponge spicules that were tested in tension, bending, and torsion (Mayer et al, 2005a;Walter et al, 2007a;Mayer and Zhou, 2009), and over several decades of loading rate in bending (Walter et al, 2007b).…”

“…1) or the concentric cylindrical composite structure (Fig. 2) is related to how energy is partitioned among the various mechanisms that are involved in deformation and fracture during energy dissipation (Mayer and Zhou, 2009). Such combinations of energy dissipation may be expressed by: The creation of new surfaces (including microcracks) in mollusk shells can be observed in works by Vincent (1990), (Ashby et al, 1995).…”

“…Surface of an untested (normally considered "smooth") section of siliceous sponge spicule); laser confocal scanning microscope (LCSM) image(Mayer and Zhou, 2009; with permission of MRS).…”

“…LCSM image of spicule fiber deformed in torsion; lower right: outer surface; top right: next layer; left: third layer; the step heights can be measured by LCSM, and are found to be very small, on the order of 0.1 µm(Mayer and Zhou, 2009; with permission of MRS).NC PRFig. 6-Schematic radial cross-section of a typical bivalve showing (dark outer curved line) a protective thin organic skin, the periostracum, followed by a prismatic layer (PR) and an inner nacreous layer (NC).…”

“…SEM image of fibril formation during deformation of spicule of E. aspergillum(Mayer and Zhou, 2009; with permission of MRS).…”