Normalised fatigue and fracture properties of candidate titanium alloys used in the pressure hull of deep manned submersibles

Abstract

The current available design rules of submersible structures from ship classification societies are based on the philosophy of strength design. Nowadays, higher requirements have been made for improved safe and economic design and operation of the submersibles, and the material selection criterion has paid more attention to the synthetic properties of materials of interest including fatigue and fracture properties of materials. Titanium alloys with relatively high ductility are widely used in pressure hull of deep manned submersibles nowadays. Much work should be devoted to systematic investigation of properties evaluation for candidate titanium alloys for submersible structures. This paper gives experimental results of fatigue and fracture properties of two candidate titanium alloys potentially used in pressure hull of deep manned submersibles. Test results are discussed by normalisation considering strength of the material which is an effective way to evaluate fatigue and crack growth properties of two materials. And to save cost and material test time in the future, an improved crack growth rate model proposed by the authors is used for prediction and unification of wide range of their crack growth rates. The comparisons between test data and prediction curves agree very well, which validate that the improved crack growth rate model can be used for prediction and unification of crack growth property of Ti80 and TC4 ELI at different load ratios.