Fatigue crack growth rate determination of graded titanium alloys and the influence of gradient for propagation life

To make sense of the crack growth rate distribution in graded material, a standard three-point bending fatigue test was performed on two groups of cracked graded titanium alloys TC11-TC4 and TA15-TA2. Test results show that the same components in different parts of graded structure shear an identical propagation property and the Paris formulas of the four kinds of 3D printing titanium alloy have been determined. The variation distribution of elastic modulus influences the stress intensity factor and inhibits the propagation of crack in the lower modulus side. During influence thickness of transition layer, propagation rate is between that of the two components and varies continuously, proving that gradient is able to eliminate the interface effect in the connection of dissimilar materials. A mixing law based on volume rate has been proposed to describe the distribution of crack propagation rate. In the test under constant periodic load, there was a remarkable difference in the propagation life of specimens only propagated along different directions. It means damage tolerance in graded structures can be improved with a reasonable arrangement of the gradient. The variation distribution of modulus and fatigue property both influence the propagation lives.