title: Isotropic microscale mechanical properties  of coral skeletons.
abstract: Scleractinian corals are a major source of biogenic calcium carbonate, yet the relationship between their skeletal microstructure and mechanical properties has been scarcely studied. In this work, the skeletons of two coral species:solitary Balanophyllia europaea and colonial Stylophora pistillata, were investigated by nanoindentation. The hardness HIT and Young's modulus E(IT) were determined from the analysis of several load-depth data on two perpendicular sections of the skeletons: longitudinal (parallel to the main growth axis) and transverse. Within the experimental and statistical uncertainty,the average values of the mechanical parameters are independent on the section's orientation. The hydration state of the skeletons did not affect the mechanical properties. The measured values, EIT in the 76-77 GPa range, and H(IT) in the 4.9–5.1 GPa range, are close to the ones expected for polycrystalline pure aragonite. Notably, a small difference in H(IT) is observed between the species. Different from corals, single-crystal aragonite and the nacreous layer of the seashell Atrina rigida exhibit clearly orientation-dependent mechanical properties. The homogeneous and isotropic mechanical behaviour of the coral skeletons at the microscale is correlated with the microstructure,observed by electron microscopy and atomic force microscopy, and with the X-ray diffraction patterns of the longitudinal and transverse sections.
authors.forename: Luca
authors.initials: L
authors.lastname: Pasquini
authors.forename: Alan
authors.initials: A
authors.lastname: Molinari
authors.forename: Paola
authors.initials: P
authors.lastname: Fantazzini
authors.forename: Yannicke
authors.initials: Y
authors.lastname: Dauphen
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Cuif
authors.forename: Oren
authors.initials: O
authors.lastname: Levy
authors.forename: Zvy
authors.initials: Z
authors.lastname: Dubinsky
authors.forename: Erik
authors.initials: E
authors.lastname: Caroselli
authors.forename: Fiorella
authors.initials: F
authors.lastname: Prada
authors.forename: Stefano
authors.initials: S
authors.lastname: Goffredo
authors.forename: Matteo
authors.initials: M
authors.lastname: Di Giosia
authors.forename: Michela
authors.initials: M
authors.lastname: Reggi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Falini
mesh_terms: D060105:Animal Shells / Q000502:physiology* / Q000648:ultrastructure*; D000818:Animals; D016880:Anisotropy; D037421:Anthozoa / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure*; D055119:Elastic Modulus / Q000502:physiology; D006244:Hardness / Q000502:physiology; D008954:Models, Biological; D016062:Porosity; D013045:Species Specificity; D013314:Stress, Mechanical