In this study, the fatigue crack growth resistance of butt joints obtained by PMMC company was evaluated. It is considered that there are two kinds of aluminum alloy matrix/alumina particles: AA606 1/Al2O3/20p and AA7005/Al2O3/ 10p, while the docking efficiency of fire department AA6061/Al2O3/20p is 72%. At the same time, the elongation at break and the hardened joint are higher than the matrix material. On the contrary, the low cycle fatigue life is slightly reduced, and the base material is PMMCs.

The purpose of this work is to introduce and analyze that there are two different load ratios of R = Kmin/Kmax for the friction stir welding butt joint of PMMC company and parent company in FCG experiment, in which the lowest and highest stress intensity factors of Kmin and Kmax are at the crack tip respectively, and there are two possible crack positions under scanning electron microscope, namely weld nugget and thermo-mechanical affected zone (TMAZ), so as to evaluate the interaction of crack particles and the crack growth mechanism under load level. Different conditions (parent material/combination, Russian ratio, crack location, crack propagation mode) are discussed in order to quote the argument of simple crack closure. Both the classical Elber method and the recent method are based on the concept of partial crack closure (adjusting performance ratio, ACR company, 2/π method).