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

Quasi-static and dynamic compression and three-point bending tests have bee n carried out on Haliotis rufescens (abalone) shells. The mechanical respon se of the abalone shell is correlated with its microstructure and damage me chanisms. The mechanical response is found to vary significantly from speci men to specimen and requires the application of Weibull statistics in order to be quantitatively evaluated. The abalone shell exhibited orientation de pendence of strength, as well as significant strain-rate sensitivity; the f ailure strength at loading rates between 10 x 10(3) and 25 x 10(3) GPa/s wa s approx. 50% higher than the quasi-static strength. The compressive streng th when loaded perpendicular to the shell surface was approx. 50% higher th an parallel to the shell surface. The compressive strength of abalone is 1. 5-3 times the tensile strength (as determined from flexural tests), in cont rast with monolithic ceramics, for which the compressive strength is typica lly an order-of-magnitude greater than the tensile strength. Quasi-static c ompressive failure occurred gradually, in a mode sometimes described as "gr aceful failure". The shear strength of the organic/ceramic interfaces was d etermined to be approx. 30 MPa by means of a shear test. Considerable inela stic deformation of the organic layers (up to a shear strain of 0.4) preced ed failure. Crack deflection, delocalization of damage, plastic microbuckli ng (kinking), and viscoplastic deformation of the organic layers are the mo st important mechanisms contributing to the unique mechanical properties of this shell. The plastic microbuckling is analysed in terms of the equation s 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 rig hts reserved.