Problem

Limited data exists to study fatigue crack growth in laser engineered net shaped (LENS) fabricated Ti-6AL-4V alloys to base damage tolerant designs on. This hinders widespread adoption of LENS for high-integrity structural applications.

R&D Analysis

Researchers from General Dynamics, the Air Force Research Laboratory, Worcester Polytechnic Institute, Nutonian Inc., Babcock Power and the Advanced Photon Source (APS) used high-energy absorption contrast microtomography at the 1-ID X-ray beamline at the U.S. Department of Energy’s APS at Argonne National Laboratory to study fatigue cracks in-situ. 3D images were taken with micron-level resolution under load and at different stages of crack propagation. Fractured samples were elevated using ex-situfractography, and in-situ results were compared to conventional measurements based on compliance and direct current potential drop.

Result

X-ray microtomography, particularly when combined with ex-situ fractographic analysis can accurately calculate local small fatigue crack growth rates in LENS printed alloys. Local crack growth variations indicated the need for non-destructive and 3-D observations to accurately understand fatigue crack growth in LENS fabricated Ti-Gal-4V. In-situ X-ray measurements can confirm and/or highlight deficiencies in conventional defect measurement techniques.

Benefit of Working with Argonne

3-D microtomography was found to provide higher-resolution data of crack formation over time and with more accuracy of growth rates at earlier stages of crack growth than traditional ex-situ striation measurements.

More Information

“Characterization of fatigue crack growth behavior in LENS fabricated Ti-6Al-4V using high-energy synchrotron X-ray microtomography,” Additive Manufacturing, 12, 132-141 (2016). DOI: 10.1016/j.addma.2016.09.002