Relationships of Egg Specific Gravity and Shell Thickness to Quasi-static Compression Tests

Abstract

The study was designed to determine the relationships of egg specific gravity and shell thickness to various mechanical properties of eggs as measured during quasi-static compression. To establish the relationships over a wide range of measurements of egg shell thickness and specific gravity, two ages of hens were exposed to a series of abrupt increases in environmental temperature. Eggs were thus available from 8 and 14 month old Hy-Line W-36 hens at 2.5-3.0° C. increments from 21.5 to 35° C. The hens were exposed to each temperature for one week. A total of 899 eggs were used. Specific gravity was precisely measured for each egg using the method based on Archimedes’ principle. A table model Instron was used for the quasi-static compression tests. The various parameters were measured during compression of the eggs at the equator. After breaking the eggs, shell thickness was measured at the equator.Most of the mechanical properties of egg shells observed by quasi-static compression tests showed significant and high correlation with egg specific gravity and shell thickness. Therefore, specific gravity and shell thickness are valid measurements to indicate shell strength of eggs over a wide range of strengths including weak egg shells. “Reference shell stiffness” (an observation taking into account the diameter of the egg) had correlation coefficients as high as those for “shell stiffness.” A parameter of “elastic stiffness” (calculated from the inflection point) was highly correlated with most physical and mechanical properties of egg shells.