In-situ measurement of near-tip fatigue crack displacement variation in laser melting deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

Laser melting deposition (LMD) is an attractive additive manufacturing technique for fabricating titanium alloy components. A variety of distinct layer bands, heat affected bands (HABs), were found in the LMDed sample, which lead to a periodic fluctuation in the fatigue crack growth rate. In this paper, an in-situ fatigue testing was performed to investigate the crack tip opening displacement (CTOD) variation within a full loading cycle. Digital image correlation (DIC) technique was implemented for obtaining the displacement fields at the vicinity of the crack tip. The crack closure phenomenon is observed from the CTOD variation and the crack opening stress level is different between HAB and non-HAB zone. Another key difference between HAB and non-HAB zone is the value of CTOD when the crack is opening. Besides, the variation of the CTOD loop and its influence on fatigue crack growth rate were also discussed in detail.