Editing Ivory (section)

== Mechanical characteristics ==
While many uses of ivory are purely ornamental in nature, it often must be carved and manipulated into different shapes to achieve the desired form. Other applications, such as ivory piano keys, introduce repeated wear and surface handling of the material. It is therefore essential to consider the mechanical properties of ivory when designing alternatives.

Elephant tusks are the animal's incisors, so the composition of ivory is unsurprisingly similar to that of teeth in several other mammals. It is composed of dentine, a biomineral composite constructed from collagen fibers mineralized with [[hydroxyapatite]].<ref name=":0" /> This composite lends ivory the impressive mechanical properties—high stiffness, strength, hardness, and toughness—required for its use in the animal's day-to-day activities. Ivory has a measured hardness of 35 on the [[Vickers hardness test|Vickers scale]], exceeding that of bone. It also has a [[flexural modulus]] of 14 GPa, a [[flexural strength]] of 378 MPa a [[fracture toughness]] of 2.05 MPam<sup>1/2</sup>.<ref name=":1">{{Cite journal |last1=Vollrath |first1=Fritz |last2=Mi |first2=Ruixin |last3=Shah |first3=Darshil U. |date=January 2018 |title=Ivory as an Important Model Bio-composite |journal=Curator: The Museum Journal |volume=61 |issue=1 |pages=95–110 |doi=10.1111/cura.12236 |issn=0011-3069|doi-access=free }}</ref> These measured values indicate that ivory mechanically outperforms most of its most common alternatives, including celluloid plastic and [[polyethylene terephthalate]].<ref name=":1" />

Ivory's mechanical properties result from the microstructure of the dentine tissue. It is thought that the structural arrangement of mineralized collagen fibers could contribute to the checkerboard-like Schreger pattern observed in polished ivory samples.<ref name=":0" /> This is often used as an attribute in ivory identification. As well as being an optical feature, the Schreger pattern could point towards a micropattern well-designed to prevent crack propagation by dispersing stresses.<ref name=":1" /> Additionally, this intricate microstructure lends a strong anisotropy to ivory's mechanical characteristics. Separate hardness measurements on three orthogonal tusk directions indicated that circumferential planes of tusk had up to 25% greater hardness than radial planes of the same specimen.<ref name=":2">{{Cite journal |last1=Cui |first1=F.Z. |last2=Wen |first2=H.B. |last3=Zhang |first3=H.B. |last4=Li |first4=H.D. |last5=Liu |first5=D.C. |date=December 1994 |title=Anisotropic indentation morphology and hardness of natural ivory |url=http://dx.doi.org/10.1016/0928-4931(94)90035-3 |journal=Materials Science and Engineering: C |volume=2 |issue=1–2 |pages=87–91 |doi=10.1016/0928-4931(94)90035-3 |issn=0928-4931}}</ref> During hardness testing, inelastic and elastic recovery was observed on circumferential planes while the radial planes displayed plastic deformation.<ref name=":2" /> This implies that ivory has directional [[viscoelasticity]]. These anisotropic properties can be explained by the reinforcement of collagen fibers in the composite oriented along the circumference.<ref name=":2" />