Using marker bands in additively manufactured Ti-6Al-4V to measure small fatigue crack growth rates and equivalent initial damage sizes

Additive manufactured (AM) structural parts are being increasingly used within Defence platforms across all domains. In the air domain, it is necessary to correctly validate the durability and damage tolerance analysis tools used for certification and sustainment of AM parts. This is emphasised by MIL‑STD‑1530Dc1 and the United States Air Force structures bulletin EZ‑SB‑19‑001. One difficulty with this is that AM production processes are known to lead to multiple different types of discontinuities which can nucleate fatigue cracks. Depending on the size of these discontinuities, they have the potential to significantly reduce the fatigue life of the AM part.

The focus of this work is on demonstrating the viability of using marker bands to assist with obtaining both crack growth curves and small crack growth rate data and equivalent initial damage size distributions for AM Ti‑6Al-4V. This technique has previously been used successfully in many wrought aluminium components and full-scale tests. The work here showed that it was possible to design effective marker bands for AM Ti‑6Al‑4V. It is judged that further development of this technique would assist with correlating durability and damage tolerance tools used in the certification of this material.