A finite element analysis of the mechanical and thermal strength of avian eggs

The hot water washing of eggs has been implicated as one source of breakage. A method for estimating shell stresses during and after washing is outlined in this paper. The problem is posed mathematically as a coupled thermo-elastic problem which relates the development of internal pressure to the shrinkage of the shell and the expansion of the inner contents due to heating. Any internal pressure developed in turn stresses the eggshell. In this study we employ a finite element method to determine the effects of various parameters, including: egg size and shape, shell thickness and permeability, wash water temperature and duration of exposure. Results from this study agree closely with previous analytical results for the case of a round egg. More realistic eggshell geometries are considered in this study; the magnitude of stresses are predicted to be larger than those developed in the spherical shell model. The location of maximum stress varied with egg shape; substantial tensile stresses developed after 60 s washing. Internal pressure, and hence shell stresses, diminished rapidly upon removal of the wash water temperature at the shell surface. Incorporation of a static 10N load at the pole in conjunction with thermally-induced stresses greatly increased shell stresses, illustrating that hot water washing, combined with mechanical loads, creates a situation in which more eggs are likely to fail. A cool-down period of 30 s-60 s is predicted to diminish thermal stresses by 60–70%.