Peter W. Voisey

Physical properties of egg shells

Synopsis A method of recording the stress distribution in egg shells about an applied force is described. Results indicate that the axes of stress can be predicted by a theoretical analysis, assuming the shell is spherical. The force required to fracture a shell was not predictable. From a theoretical approach, shell thickness, ultimate tensile strength and curvature were the important factors in shell strength. An external force produced tension at the inner shell surface and compression at the outer surface at the point of contact. The maximum tensile stress was at the point of application of force and diminished radially from this point. Because the shell material is brittle and therefore weaker in tension than in compression, the shell must fracture initially at the inner surface under the point of contact. It was concluded that shell behaviour in tension is a major factor contributing to shell strength.

Physical properties of egg shells: 3. An apparatus for estimating impact resistance of the shell

Synopsis A device is described for recording the maximum force imposed, by the impact of a falling steel rod, on egg shells. Maximum force occurred at the point of shell failure. Correlation between the maximum force during impact and shell thickness were highly significant but not considered adequate for predictive purposes. It was concluded that shell thickness accounted for only part of the variation in resistance of the shell to impact.