The boundary between the initiation and the propagation phase of fatigue and the explanation of Threshold region
Mr. Ma Jianxiao
PhD candidate in the Mechanical Engineering Dept.
Date & Time
Tuesday, 12 April 2022
In fatigue, the boundary between the crack initiation and propagation phases needs to be resolved. The Manson-Coffin equation and the Paris equation are the two fundamental equations, which are used in crack-free and cracked structures, respectively. By transforming these two equations, a relatively reasonable quantitative boundary has been proposed.
When the same idea was used in a cracked structure, the crack growth rate has been calculated by the Manson-Coffin equation containing two parameters——the magnitude of stress intensity factor and the stress ratio. Through the analysis of stress ratio and residual stress, a plausible meaning of the threshold region is explained. Pre-overload experiments show that overload is the cause of the threshold region.