Beyond the orthogonal
On the influence of build orientation on fatigue crack growth in SLM Ti-6Al-4V
CD Rans (TU Delft - Structural Integrity & Composites)
J. Michielssen (TU Delft - Education AE)
Megan Walker (TU Delft - Structural Integrity & Composites)
W. Wang (TU Delft - Structural Integrity & Composites)
L. ’t 't Hoen-Velterop (Royal Netherlands Aerospace Centre NLR)
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Abstract
A challenge in developing an in-depth understanding of the crack growth resistance of Additively Manufactured materials is the fact that their mechanical properties have been shown to be both process and part-geometry dependent. Up to now, no studies have investigated the influence of off-axis (beyond the three orthogonal build orientations) orientations on the fatigue crack growth behaviour of selective laser melted Ti-6Al-4V. Furthermore, the widespread use of compact tension specimens for investigating the material behaviour generates data more suitable for plane-strain conditions, rather than the plane-stress state which is more applicable to many lightweight aerospace structures. To address this gap in knowledge, a comprehensive study was carried out to investigate the influence of off-axis build direction in thin SLM Ti-6Al-4V plates, with a focus on the influence of columnar grain orientation on the fatigue crack growth behaviour. It was found that although a macroscopic columnar grain structure is visible on the specimens, it had no discernible influence on the crack growth resistance when the specimen had undergone a stress relieving or HIP heat treatment.
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