Effect of Pre-strain on Failure Assessment of Titanium Pressure Vessel with Crack

To understand the effect of pre-strain on the integrity assessment of titanium structure with crack, the dependence of tensile mechanical parameters, fracture toughness, failure assessment diagram (FAD) on pre-strain was focused. Firstly, tensile tests reveal that with increasing the pre-strain value, the yield stress and the yield-ultimate strength ratio increase, but the ductility decreases, and the fracture toughness decreases. Then, based on finite element (FE) analyses of compact tension (CT) specimen and titanium pressure vessel with crack, the plastic zone near the crack tip decreases with increase of pre-strain, resulting in the decrease of J-integral. Moreover, the BS 7910:2013 failure assessment curves (FAC) of Options 1 and 3 vary with pre-strain, and the acceptable area decreases. Therefore, with increase of pre-strain, the reserve factor of yield stress increases but that of fracture toughness decreases significantly. In brief, the pre-strain affects the failure assessment of titanium pressure vessel with crack, and needs to be considered in the integrity assessment.