In structural engineering and material science, fast fracture is a term given to a phenomenon in which a flaw (such as a crack) in a material expands quickly, and leads to catastrophic failure of the material. Stress acting on a material when fast fracture occurs is less than the material's yield stress. A very representative example of this is what happens when poking a blown up balloon with a needle, that is, fast fracture of the balloon's material.
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