In
structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and ca ...
and
material science, fast fracture is a phenomenon in which a flaw (such as a crack) in a material expands quickly, and leads to
catastrophic failure
A catastrophic failure is a sudden and total failure from which recovery is impossible. Catastrophic failures often lead to cascading systems failure. The term is most commonly used for structural failures, but has often been extended to many othe ...
of the material. It proceeds in high speed and requires a relatively small amount of accumulated
strain energy
In physics, the elastic potential energy gained by a wire during elongation with a tensile (stretching) force is called strain energy. For linearly elastic materials, strain energy is:
: U = \frac 1 2 V \sigma \epsilon = \frac 1 2 V E \epsilon ...
, making it a dangerous failure mode.
Flaw
Stress acting on a material when fast fracture occurs is less than the material's
yield stress
In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...
. 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. The energy in the balloon comes from the compressed gas inside it and the energy stored in the rubber membrane itself.
The introduction of the flaw, which in this case is the pin prick, would lead to the explosion as the membrane fails by fast fracture.
However, if the same flaw is introduced to a balloon with less energy - as in the case of a partially inflated balloon - the fast fracture will not occur, unless the balloon is punctured progressively so that it reaches a critical pressure at which fast fracture occurs.
The occurrence of fast fracture can depend on the material. For instance, it transpires in the cases of brittle materials with less capacity for deformation even if the flaw only involves small defects caused by the manufacturing process.
See also
*
Yield (engineering)
In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and w ...
References
Mechanical failure
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