The deceleration and acceleration of crack propagation following tensile overload and hold time

The effect of the hold time of a tensile overload on crack propagation behaviours following the overload was investigated. In the study, the crack propagation behaviour after the overload was observed under constant amplitude load with stress ratio zero and negative, respectively. The result of the study shows that the fatigue life, the deceleration and acceleration of the crack propagation depends on the magnitude, the hold time of the overload and the shape of the crack tip as well as the stress ratio of the constant amplitude load following the overload. The deceleration occurs if the compressive residual stress develops in the zone affected by the overload in front of the crack tip. Whereas, if the tensile residual stress develops in that zone, the crack is accelerated, and the fatigue life is shortened. In addition, the shape and the displacement of the crack tip affect the residual stress condition in front of the crack tip, and the crack can be advanced by the hold time of the overload, thus, it also enhances the acceleration of the crack propagation following the overload.