Effect of ARB Processing on Fatigue Crack Closure in Commercially Pure Titanium

Fatigue crack closure in commercially pure titanium sheets severely deformed using the accumulative roll-bonding (ARB) process were investigated. Sheet processed through 6 cycles of ARB consists of fine equiaxed grains and elongated lamellar grains and shows a high 0.2% proof stress of 790 MPa. Fatigue crack closure was not observed in the ARB processed sheet. The effective threshold stress intensity factor ranges, Delta K-th.eff, of the ARB processed sheets and starting sheet are nearly the same. On the other hand, the resistance of the fatigue crack growth rate of the ARB processed sheet is higher than that of the starting sheet. It was found that ARB increases the resistance for the fatigue crack propagation but has no effect on the onset of propagation.