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J Mech Behav Biomed Mater. 2009 Dec;2(6):607-12. doi: 10.1016/j.jmbbm.2009.04.003. Epub 2009 May 4.

Interfacial shear strength in abalone nacre.

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Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093-0411, USA.


The shear strength of the interface between tiles of aragonite in the nacre of red abalone Haliotis rufescens was investigated through mechanical tensile and shear tests. Dog-bone shaped samples were used to determine the tensile strength of nacre when loaded parallel to the plane of growth; the mean strength was 65 MPa. Shear tests were conducted on a special fixture with a shear gap of 200 microm, approximately 100 microm narrower than the spacing between mesolayers. The shear strength is found to be 36.9+/-15.8 MPa with an average maximum shear strain of 0.3. Assuming the majority of failure occurs through tile pull-out and not through tile fracture, the tensile strength can be converted into a shear strength of 50.9 MPa. Three mechanisms of failure at the tile interfaces are discussed: fracture of mineral bridges, toughening due to friction created through nanoasperities, and toughening due to organic glue. An additional mechanism is fracture through individual tiles.

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