title: Nature's technical ceramic: the avian eggshell.
abstract: Avian eggshells may break easily when impacted at a localized point; however, they exhibit impressive resistance when subjected to a well-distributed compressive load. For example, a common demonstration of material strength is firmly squeezing a chicken egg along its major axis between one's hands without breaking it. This research provides insight into the underlying mechanics by evaluating both macroscopic and microstructural features. Eggs of different size, varying from quail (30 mm) to ostrich (150 mm), are investigated. Compression experiments were conducted along the major axis of the egg using force-distributing rubber cushions between steel plates and the egg. The force at failure increases with egg size, reaching loads upwards of 5000 N for ostrich eggs. The corresponding strength, however, decreases with increasing shell thickness (intimately related to egg size); this is rationalized by a micro-defects model. Failure occurs by axial splitting parallel to the loading direction-the result of hoop tensile stresses due to the applied compressive load. Finite-element analysis is successfully employed to correlate the applied compressive force to tensile breaking strength for the eggs, and the influence of geometric ratio and microstructural heterogeneities on the shell's strength and fracture toughness is established.
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, CA, USA.
authors.forename: Eric N
authors.initials: EN
authors.lastname: Hahn
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, CA, USA.
authors.forename: Vincent R
authors.initials: VR
authors.lastname: Sherman
authors.affiliation: Mechanical and Aerospace Engineering Department, University of California, San Diego, CA, USA.
authors.forename: Andrei
authors.initials: A
authors.lastname: Pissarenko
authors.affiliation: Mechanical and Aerospace Engineering Department, University of California, San Diego, CA, USA.
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Rohrbach
authors.affiliation: Biomaterials Laboratory, Military Institute of Engineering, Rio de Janeiro, Brazil.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Fernandes
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, CA, USA mameyers@eng.ucsd.edu.|Mechanical and Aerospace Engineering Department, University of California, San Diego, CA, USA.|Nanoengineering Department, University of California, San Diego, CA, USA.
authors.forename: Marc A
authors.identifier: 0000-0003-1698-5396
authors.initials: MA
authors.lastname: Meyers
mesh_terms: D000818:Animals; D002516:Ceramics / Q000737:chemistry*; D002645:Chickens; D019245:Compressive Strength; D004528:Egg Shell / Q000737:chemistry*; D010063:Ovum / Q000737:chemistry*; D013314:Stress, Mechanical
keywords: eggshell; fracture toughness; hoop stress; strength