Mechanical Fatigue

Mechanical fatigue is demonstrated in rubbery materials by a progressive weakening of physical properties as a result of slow crack growth during application of dynamic loads or deformations. The most obvious of the changes is a gradual reduction in stiffness. Protracted static loading causes stress relaxation and may also result in time-dependent cracking of most synthetic amorphous elastomers, but usually not natural rubber. Under a steady load natural rubber crystallizes, and the crystallites apparently prevent further growth of cracks.