Abstract: The damage tolerance properties of metal materials commonly used in aircraft structures were compared and discussed. In view of the poor damage tolerance characteristics of TC4 and TA15, two extralow interstitial (ELI) titanium alloys TC4ELI and TA15ELI were developed. A feasibility study was performed on the damage tolerance structure design for the ELI titanium alloys. The crack growth life, residual strength, and total fatigue life experiments were conducted on both the two ELI titanium alloys and common titanium alloys. The experimental results show that: compared with the common types, the ELI titanium alloys have higher fracture toughness and slower crack propagation rate, similar residual strength and total fatigue life. Under equivalent loading, the detectable crack growth life of the ELI titanium alloys is longer than that of the aluminum alloys. Consequently, in aircraft structure design, the damage tolerance method could be adopted with the ELI titanium alloys TC4ELI and TA15ELI.

Key words: titanium alloys, damage tolerance, structural design, extralow interstitial, crack growth, total fatigue life