The mechanics and mechanisms of failure of hens’ eggs

The mechanics and mechanisms of failure of hens’ eggs have been examined experimentally under contact loading conditions relevant to industrial conditions by testing eggs of known provenance in compression between stiff platens. Deformation was modelled computationally as a Hertzian contact problem between a thin walled elastic shell and a rigid plate. Contact damage was determined by scanning electron microscopy and by optical examination of transverse sections through the shell. Small stable micro-cracks were found to initiate in the contact area before structural failure, which was characterised by the propagation of one or more macroscopic cracks. Structural failure does not correspond to crack initiation, but crack propagation. Stablemicro-cracks were not detectable by routine visual inspection or acoustic resonance, and combined with inconsistent cuticle coverage these could provide a pathway for pathogens to enter the egg contents and thus compromise egg safety.