Influence of hen egg shape on eggshell compressive strength.

A b s t r a c t. Eggshell behaviour at static compression was investigated. Exact description of the eggshell contour shape was used for verification of a commonly accepted theory on the compression of bodies of convex form. Particularly, the shape of the eggshell contour was described using polar coordinates r, j, and radius of the curvature, R. Two compression axes were used to determine the rupture force, specific deformation, rupture energy and firmness. Energy absorbed by an egg at the moment of rupture was also determined. The least resistance to rupture was observed for eggs compressed between the poles. Also other quantities connected with the eggshell damage depend on the orientation of the loading force during egg compression. It was found that egg shape influenced the energy absorbed during egg loading, both in the pole and the equator planes. The other parameters were not affected by egg shape. The experiments revealed that the deformation behaviour of the eggshell was elastic. Elastic constants (39.9±8.5 GPa) and (0.345) were calculated. Two different methods were used and results of both procedures were nearly the same. Elastic constants were independent on the egg shape as well as on the loading force orientation. Presented numerical simulation of the experiments gave more detailed information on the stress state in the loaded eggshell. LS DYNA 3D finite element code was used for the simulation. K e y w o r d s: eggshell shape index, strength, elasticity, eggshell stiffness, numerical simulation