During my third year at McGill University, I was fortunate enough to be accepted into the SURE program. With a research grant by NSERC and my supervisor, Professor Mathieu Brochu, I was able to pursue my passion of emerging materials engineering technologies for the applications in the aerospace industry. The particular technology during this research was the laser powder bed fusion, to consolidate metallic components from their powdered form.
Alongside a PhD student, I studied the laser powder bed fusion process, with the goal to develop a procedure to measure the residual stress by using two different X-Ray Diffraction (XRD) machines. I took this opportunity to learn how to interpret data from XRD experiments and calculate the residual stress based on deviations in the measured lattice parameters. MATLAB became an essential tool for the visualization of residual stress measurements which helped us identify the differences in methods of evaluating residual stress. The XRD intensity plots from an annealed iron powder samples (near zero residual stress) versus a 3-D printed 316-L stainless steel sample illustrates the stark differences in stress measurements.
With this knowledge, I was able to evaluate the residual stress of printed components with different raster paths. The raster path or scanning pattern is an important processing parameters as it has a direct effect on the thermal distribution within the components during printing. Three paths were evaluated in this case: stripe, meander, and chessboard. These laser raster paths were applied to (20x20)mm stainless-steel cubes with the x-axis stress orientation shown in the figure below.
From my analysis, the meander pattern exhibited the largest residual stress in the printing direction. This outcome was expected as this pattern displayed high thermal gradients during the melting and cooling cycles in additive manufacturing. Narrow temperature peaks and large gradients was found to be the main source of residual stress that affected the final printed samples.
If you'd like to know more about how residual stress is evaluated using XRD or how the raster path influences the stress in a printed metal component, please don't hesitate to email me at: ilhanesmail@gmail.com
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