Fracture mechanisms of the Strombus gigas conch shell: II-micromechanics analyses of multiple cracking and large-scale crack bridging |
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| Affiliation: | 1. Department of Materials Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA;2. Institute of Solid State Mechanics, University of Technology Dresden, D-01062 Dresden, Germany;3. Department of Civil Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA;1. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA;2. Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USA;1. State Key Laboratory for Disaster Prevention & Mitigation of Explosion & Impact, PLA University of Science & Technology, Nanjing 210007, China;2. School of Civil & Architecture Engineering, Jishou University, ZhangJiajie, Hunan 427000, China;3. School of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China;4. Research Institute of Structural Engineering and Disaster Reduction, College of Civil Engineering, Tongji University, Shanghai 200092, China;1. State Key Laboratory for Turbulence and Complex System, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China;2. Beijing Innovation Center for Engineering Science and Advanced Technology, Peking University, Beijing 100871, China;1. Università degli Studi di Milano, Dipartimento di Scienze della Terra ‘A. Desio’, via Mangiagalli 34, Milano 20133, Italy;2. Department für Geo- und Umweltwissenschaften, Ludwig-Maximilians Universität München, Munich, Germany;3. Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071, Granada, Spain, and Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, 18100 Armilla, Spain;4. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK;1. Department of Materials Science and Engineering, University of California Berkeley, CA 94720, USA;2. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China;3. Department of Nanoengineering, Materials Science and Engineering Program, University of California San Diego, La Jolla, CA 92093, USA;4. Department of Mechanical and Aerospace Engineering, Materials Science and Engineering Program, University of California San Diego, La Jolla, CA 92093, USA |
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| Abstract: | Micromechanics analyses of the dominant energy-dissipating mechanisms responsible for the resistance to catastrophic fracture of the aragonitic shell of the giant Queen conch, Strombus gigas, are presented. The crossed lamellar microstructure of the shell is associated with a work of fracture that is three orders of magnitude higher than that of non-biogenic aragonite [J. Mater. Sci. 6 (1996) 6583]. Previous energy-based models predict that multiple “tunnel” cracks in the weak layers of the shell account for a factor of 20 of this increase in fracture energy. We show that the additional factor of ⪞300 results from the synergy between the tunnel cracking and crack bridging mechanisms, analogous to multiple energy dissipating mechanisms observed in brittle matrix composites. The theoretical models demonstrate that the microstructure of the shell of S. gigas is such that potential cracks evolve towards the desirable non-catastrophic ACK (Aveston–Cooper–Kelly) [Properties of fiber composites, Conference Proceedings 15, National Physical Laboratory, IPC Science and Technology Press, 1971] limit, a situation in which all bridging ligaments remain intact along the crack wakes. Load–deflection experiments at temperatures ranging from −120 to 200 °C suggest that a glass transition occurs within the organic (proteinaceous) phase at ∼175 °C, and demonstrate the critical role that this organic “matrix” plays in the resistance of the shell to catastrophic crack propagation. |
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