Quasi-static and dynamic mechanical response of Haliotis rufescens (abalone) shells

Quasi-static and dynamic compression and three-point bending tests have been carried out on Haliotis rufescens (abalone) shells. The mechanical response of the abalone shell is correlated with its microstructure and damage mechanisms. The mechanical response is found to vary significantly from specimen to specimen and requires the application of Weibull statistics in order to be quantitatively evaluated. The abalone shell exhibited orientation dependence of strength, as well as significant strain-rate sensitivity; the failure strength at loading rates between 10 x 10(3) and 25 x 10(3) GPa/s was approx. 50% higher than the quasi-static strength. The compressive strength when loaded perpendicular to the shell surface was approx. 50% higher than parallel to the shell surface. The compressive strength of abalone is 1.5-3 times the tensile strength (as determined from flexural tests), in contrast with monolithic ceramics, for which the compressive strength is typically an order-of-magnitude greater than the tensile strength. Quasi-static compressive failure occurred gradually, in a mode sometimes described as graceful failure. The shear strength of the organic/ceramic interfaces was determined to be approx. 30 MPa by means of a shear test. Considerable inelastic deformation of the organic layers (up to a shear strain of 0.4) preceded failure. Crack deflection, delocalization of damage, plastic microbuckling (kinking), and viscoplastic deformation of the organic layers are the most important mechanisms contributing to the unique mechanical properties of this shell. The plastic microbuckling is analysed in terms of the equations proposed by Argon (Treatise of Materials Science and Technology. Academic Press, New York, 1972, p. 79) and Budiansky (Comput. Struct. 1983, 16, 3). (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.