Fracture parameters analysis of compact tension specimens with deflected fatigue cracks: ZK60 magnesium alloy

Precise monitoring of crack growth and a comprehensive understanding of crack propagation rate are crucial for the evaluation of the structural integrity of magnesium alloys with defects. Different crack deflections caused by the coupling of specimen orientations and crack sizes significantly increase the challenge to magnesium alloy evaluation. In this paper, the systematic finite element analysis was conducted for compact tension (CT) specimens with deflection cracks. A wide range of geometric variations including initial crack length, crack deflection angle and crack propagation length were analyzed. Complete solutions of the stress intensity factor (K_I and K_II), T-stress and the compliance at the load line were determined. The results showed that the geometric sizes have a significant coupling effect on the fracture mechanics parameters, and the non-deflected cracked formula recommended by the ASTM standard is not applicable to the deflection crack specimens. Then, a prediction method of kinked fatigue crack length of CT specimen based on the compliance multiplier method was proposed. To further verify the importance of the fracture parameters obtained, CT fatigue crack growth (FCG) tests of ZK60 magnesium (Mg) alloy under different orientations and initial crack sizes were carried out. The FCG rate curves of ZK60 Mg alloy under different crack growth driving forces were compared and illustrated. The developed compliance multiplication method can accurately predict the real-time crack propagation length.