The hen's egg: Fracture of shells loaded very slowly

1. Eggs were loaded at the equator, the load on each egg increasing at a constant, low rate dW/dt in the range from 8.7 to 0.39 g/s.

2. When loading continued until shell failure the mean value of the force at failure, Pf, decreased as the loading rate decreased.

3. Among eggs from a given population the mean value of the product P_fR_a was related to log ê (dW/dt) in a linear manner, where R_a is the reciprocal of the average curvature of the shell at the point of application of the load.

4. When loading had been halted shortly before the expected time of failure, delayed failure was observed in more than a quarter of the eggs.

5. The more closely the load approximated to the expected load at failure, the shorter the delay in eggs showing delayed failure.

6. There is a risk of loss of eggs through delayed shell fracture if they are stored in stacks of trays that permit some of them to bear loads that are not large enough to cause immediate fracture but are nevertheless fairly large.