Font Size: 

There is an increasing use of titanium in primary aircraft structures withbulkheads in the F-22, Super Hornet, and the Joint Strike Fighter being made oftitanium. Until recently it was thought that cracking in titanium and high strengthaerospace steels was relatively well understood. However, this paper analyses aseries of NASA, and Boeing studies into cracking in Ti-6AL-4V to reveal a weakR ratio effect with little closure in Region II. We also see that, in each case, thedata conforms to the Generalised Frost-Dugdale crack growth law. This study alsoimplies that the mechanisms driving cracking in high strength aerospace steelsand Mil Annealed Ti-6Al-4V are similar.