Mechanical properties, spectral vibrational response, and flow-field analysis of the aragonite skeleton of the staghorn
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Mechanical properties, spectral vibrational response, and flow-field analysis of the aragonite skeleton of the staghorn coral (Acropora cervicornis) Alejandro Carrasco-Pena1 • Mahmoud Omer1 • Bridget Masa1 • Zachary Shepard1 Tyler Scofield1 • Samik Bhattacharya1 • Nina Orlovskaya1 • Boyce E. Collins2 • Sergey N. Yarmolenko2 • Jagannathan Sankar2 • Ghatu Subhash3 • David S. Gilliam4 • John E. Fauth5
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Received: 30 January 2020 / Accepted: 11 September 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Understanding the structural and mechanical properties of coral skeletons is important to assess their responses to natural and anthropogenic challenges and to predict the long-term viability of hermatypic corals in a changing ocean. Here, we describe the microstructure of the critically endangered staghorn coral (Acropora cervicornis) skeleton and its mechanical properties, spectral and fluidic behavior, including uniaxial compressive strength, resistance to plastic deformation, spectral vibrational response, and flow-field analysis. We evaluated skeletons of A. cervicornis retrieved from a nursery off Broward County, Florida, USA. Optical micrographs and X-ray computed topography revealed a complex system of canals and pores that allow rapid skeletal elongation while retaining sufficient strength to withstand currents, waves, Topic Editor Morgan S. Pratchett
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00338-020-02003-8) contains supplementary material, which is available to authorized users. & Nina Orlovskaya [email protected] 1
Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA
2
Engineering Research Center for Revolutionizing Biomaterials, North Carolina A&T State University, IRC Building, Suite 242, Greensboro, NC 27411, USA
3
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
4
Department of Marine and Environmental Sciences, Nova Southeastern University Oceanographic Center, Dania Beach, FL 33004, USA
5
Department of Biology, University of Central Florida, Orlando, FL 32816, USA
and other physical forces. Compressive loading of the aragonite skeleton resulted in complex stress–strain deformation behavior; the unique pore arrangement resisted catastrophic cracks and prevented instantaneous failure. Vickers microhardness was 3.56 ± 0.31 GPa, which is typical for soft aragonite materials yet sufficient to withstand the hydraulic pressure of ocean waves. Impressions made by the diamond indenter had almost no cracks radiating from their corners, which again demonstrated the ability of the complex skeleton microstructure to suppress crack formation and growth (e.g., from the bites of grazers). Maps of the m1 mode Raman peak of identation surfaces showed evidence of residual strain. However, the m1 peak’s position barely changed (from 1083.6 cm-1 outside the impression to 1083.9 cm-1 in the center), indicating wea
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