1. Stress and Strain:
* When a material is subjected to force, it experiences stress, which is the internal force per unit area within the material.
* This stress causes the material to deform or strain, changing its shape.
2. The Breaking Point:
* Every material has a yield strength, which is the maximum stress it can withstand before it starts to deform permanently.
* Beyond the yield strength, the material enters a plastic deformation stage, where it continues to deform even after the stress is removed.
* Eventually, the material reaches its fracture strength, where it can no longer withstand the stress and begins to break.
3. The Crack Forms:
* When a crack forms, it releases the stored energy within the material, causing a sudden change in the material's structure.
* The energy released creates vibrations that travel through the material and into the surrounding air.
4. Sound Waves:
* These vibrations in the air are what we perceive as sound.
* The frequency of the vibrations determines the pitch of the sound.
* A crack usually produces a high-pitched, sharp sound because the vibrations are very rapid.
Factors Affecting the Crack Sound:
* Material: Different materials have different fracture strengths and sound properties. A crack in a brittle material, like glass, will sound different from a crack in a ductile material, like metal.
* Size and Shape of the Crack: The size and shape of the crack affect how much energy is released and the frequency of the vibrations produced.
* Speed of Fracture: The faster the crack propagates, the higher the frequency of the sound waves.
In essence, a crack sound is the audible manifestation of a sudden, violent change in the structure of a material, caused by the release of stored energy.