Fracture and fatigue
fracture mechanics
fracture calculations
fatigue life
fatigue calculations

Fatigue 1

Fatigue is failure that occurs in structures that undergo repeated cyclic stress, for example bridges and connecting rods.

In fatigue it is possible for failure to occur at stresses much lower than the yield strength.

Fatigue is responsible for about 90% of all metallic component failures, and it is also possible for polymers and ceramics to fail by fatigue.

It is catastrophic in that it occurs without warning because it is a brittle fracture (with little or no plastic deformation) that occurs in materials that are normally ductile.

There are three different modes of fatigue loading, shown below:

Graph: reversed stress cycle

Reversed stress cycle

Repeated stress cycle

Random stress cycle

There are a number of fatigue parameters used to characterise the fluctuating stress cycle, shown below:

Graph: stress cycle

Mean stress

Stress range


Stress ratio R

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