[Physics] Why do chocolate bars usually break at the cleavages

Question

Why do chocolate bars usually break at the cleavages?

The chocolate bar is less thick at cleavages. How can we relate thickness and fracture point of chocolate bar?

Answer 1

When you tries to break a chocolate bar, a shear stress is applied to the chocolate bar. Once the chocolate reaches its yield strength, the stress at which a material begins to deform plastically, it will break. Thicker materials have higher yield strength than thinner ones, so the thinner cleavages will break first.

Strength of Materials