Research of Helicoidal Layup of Clam Shell

Abstract

Molluscan shell is a kind of natural composite with excellent fracture strength and fracture toughness, which can be attributed to its unique microstructures. Scanning electron microscope (SEM) observation shows that Clam shell is a bio-ceramic composite consisting of aragonite and organic materials. These aragonite and organic materials distribute in the shell in the form of layers parallel with the surface of the shell. The observation also shows that the aragonite layers contain numerous thin and long aragonite strips, which are dozens of nanometers in diameter and can be regarded as aragonite fibers. These aragonite fibers align in the layers with different orientations. A kind of particular helicoidal layup of these aragonite fibers is found. The maximal pull-out force of the helicoidal layup of the aragonite fibers is analyzed, which accounts for the high fracture toughness of the shell. A comparative experiment for the maximal pull-out forces of both the helicoidal and the 0° layups is conducted, which shows that the maximal pull-out force of the helicoidal layup is markedly larger than that of the conventional 0° layup.