Crack shape evolution of single edge through cracked specimens under mode-I loading

Crack shape evolution of single edge through cracked specimens under mode-I loading is studied by means of theoretical analysis, numerical simulation and experimental investigation. Firstly, based on the Paris formula and taking into account the effective stress intensity factor range ratio (U), which characterizes the degree of crack closure, a modified crack growth rate equation is derived. Then, taking the 10 mm thick Al 6061-T6 alloy plate as an example, numerical simulation analysis is conducted. The shape change of crack front during crack propagation is characterized by tunnel depth and surface angle. Finally, fatigue crack growth test is conducted adopting the crack front marking technique to validate the simulation results. The results indicate that the crack growth rate is mainly controlled by the maximum stress intensity factor (K_max) and the U under a certain stress ratio (R). The crack propagation mainly includes two stages, the initial crack propagation stage and the stable crack propagation stage. During the initial crack propagation stage, the crack growth rate in the central layer is greater than that in the surface layer. After approximately 4 mm of crack growth in the central layer, the crack propagation enters the stable stage. In the stable crack propagation stage, the growth rate of the entire crack front is similar, and the shape of the crack front remains almost unchanged.