2 A New Formula on Fatigue Crack Propagation

Although many researches have been done on the cracked body in the expansion of low stress and many theories and solutions are also put forward, the incidents of cracks expanding to destruction still occur from time to time, thus mechanism of crack expanding needs for further study. Because the cyclic load acting on the cracked body is a dynamic load, the crack growth mechanism is revealed from the view of Dynamics. So, new expansion formula of the crack is proposed and the physical meanings of parameters in the formula are explained. The theory provides a solid mechanical foundation for the remaining life of the cracked body.