On the topic on the structure of the eggshell, have you realized that if damage to the shell is not so serious, while the shell is cracked, the content of the eggs do not leak out from the shell? This is because of a thin organic membrane on the inner side of the shell, which can remain intact even when the shell is cracked. Cracking of the shell is hypothesized to occur along these imperfections of the eggshell.
When visualized under a scanning electron microscope, clear “ridges” and “cracks” can be seen on the eggshell. In that case, shouldn’t the eggshell be resistant to cracking, since strong ionic interactions between the calcium and carbonate ions have to be broken for cracking to occur? However, the crystal lattice in the eggshell has many imperfections.
You may then wonder, the egg shell is made up of calcium carbonate, an ionic solid. This is because of surface curvature the equator has the largest radius of curvature, allowing for a smaller change in the geometry of the egg when compressed, and also better distribution of stresses within the eggshell. However, that is exactly the opposite of reality! Eggs are the strongest at the equator, followed by the base, and crack most easily at the tip. Intuitively, we may say it is the tip of the egg, which resembles a conical structure. Which part of the egg is most likely to crack when dropped from the same height? That may be a question some people have considered. The egg shell is compressed and distorted by the collision, and due to the application of the impact force at such a short time interval, the stresses in the egg shell cannot be redistributed quickly enough for the eggshell to crack under the stress. Observation of a high speed video of egg cracking allows us to see the result of such a dynamic impact. Studies show a value of 0.0004s of duration of impact, where a relatively large force is delivered to the eggshell in a very short interval time.įigure 1: Deformation of eggshell upon dynamic impact. When you drop an egg onto a table, what happens is the exertion of force onto the egg shell in a very short interval. However, have you actually considered the mechanism behind egg cracking? However, egg shells are always so brittle, easily cracked even when dropped from just 2cm onto a hard table. We have all had that feeling before: opening a box of eggs, and realizing that more than half had been broken on the way home from the supermarket, whether it is accidentally hitting the box against the wall, or dropping the entire egg carton on the floor, eggs are delicious, present in the cuisines of almost every culture, and an indispensable ingredient in baking.
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