Shell, a naturally engineered egg packaging: Estimated for strength by non-destructive testing for elastic deformation

Eggshell is a naturally engineered packaging of its interior content and prediction of the egg fracture force (F) under non-destructive elastic shell deformation (D) remains a challenge. Specifically, since shell deflection function under a constant load is linear, it is difficult to calculate the maximum point for F and the respective value of D. The aim was to solve this problem experimentally by employing a measurement instrument commonly used to analyse the deformation of metals and alloys. The experiments were conducted on chicken eggs aligned in their morphological parameters. A curvilinear characteristic of the change in the function F = f(D), was achieved at extremely low shell compression speeds (0.010 to 0.065 mm s-1). This enabled us to (i) describe the obtained functions accurately with Gaussian curves; (ii) expand the range of non-destructive load on a chicken egg to 30 N; and (iii) develop empirical equations for a reasonably accurate prediction of maximum shell deformation (R2 = 0.906) and shell strength (R2 ≈ 1). It is suggested that it is possible to calculate shell strength by measuring its deformation at five points that corresponded to non-destructive loads of 10, 15, 20, 25 and 30 N. The methodological approach proposed can be used for the development of an effective shell strength calculation procedure by non-destructive testing. It depends on the appropriate tool for assessing and controlling the elastic shell deformation as well as the features of strength properties of the studied eggs.