Experimental estimation of fatigue crack growth rate and study of stress ratio effect in thin aluminium alloy plates

摘要

Fatigue crack growth rate (FCGR) is expressed in terms of ΔJ (cyclic J-integral), ΔCTOD (cyclic crack tip opening displacement) and ΔCMOD (cyclic crack mouth opening displacement) instead of ΔK (cyclic stress intensity factor) in the well-known Paris equation. Conducting several tests on CT specimens made of aluminium alloy with specific chemical composition and having 2.9mm thickness according to standard test method ASTM E647, the proposed model is examined. The experimental results show that ΔJ and ΔCTOD, contrary to ΔK and ΔCMOD which are constant in R-ratio variations, vary with the variations of R-ratio in the range R=0.3 to R=0.6. Therefore, there is no need to enter R parameter directly in the well-known Paris equation if ΔJ or ΔCTOD parameter is used instead of ΔK in this equation. The constants of these equations are independent of loading unlike the constants of Paris equation. Finite element analysis is also performed and the results are compared with the experimental results.