Effects of control mode and R-ratio on the fatigue behaviour of a metal matrix composite

Thick specimens of [0]32 SiC/Ti-15-3 were cycled under a variety of loading conditions. Specimens were fatigued in strain- and load-controlled modes at both R = 0 (zero-tension) and R = −1 (fully reversed) loading ratios. In addition, a hybrid strain-controlled mode at R = 0 was used to simulate the true strain-controlled behaviour. The strain-controlled specimens had longer lives compared with the load-controlled specimens when cycled at an R-ratio of zero. Under fully reversed loading, there was no difference between the strain- and load-controlled modes. The hybrid strain-controlled data were found to approximate the load-controlled data better, rather than the true strain-controlled situation. Damage occurred through transverse fibre cracks for R = 0 loading for both the load- and strain-controlled modes. However, fully reversed loading caused matrix cracking to be the operative damage mechanism.