Aerospace Engineering Brown Bag Lecture Series, Jonathan DeLozier and Aman Tanna

The October 1st Aerospace Engineering Brown Bag Lecture Series, featured Jonathan DeLozier and Aman Tanna.
Jonathan DeLozier presented,
"CFD Analysis of Hypersonic Converging Diverging Nozzle"
When designing a nozzle for flow field generation via a shock tunnel, it is essential to ensure proper geometry and subsequently proper flow characteristics. This presentation details a computational fluid dynamics based analysis used to study the performance of such a nozzle and verify its geometry. In particular, this presentation focuses on a converging-diverging nozzle designed using the axi-symmetric Method of Characteristics to produce uniform, Mach 5 flow. Discussion includes boundary condition selection, grid generation, solver selection, simulation results, and solution validation. Additionally, comparisons are made between results from various turbulence models and next steps for this analysis are discussed.
Aman Tanna presented,
"Data-Driven Process-Structure-HCF strength models for Additively manufactured Alloy 625"
This research aims to investigate the influence of the microstructure, defect features, and surface roughness on the high cycle fatigue (HCF) strength of IN625 manufactured using Laser Powder Bed Fusion (L-PBF) additive manufacturing (AM) process. 11 AM builds each containing several fatigue test specimens with axis of specimen oriented in either the z-direction (build direction) or transverse direction were manufactured to explore the influence of variations in laser scan speed, hatch spacing, and L-PBF machine system. These processing conditions resulted in variations in microstructure, defect features, and surface roughness, all of which can influence fatigue strength. All specimens were stress-relieved before removal from build plate and then a hot isostatic press- ing (HIP) was performed. Specimens were tested in either as-is condition, with no further machin- ing or polishing, or in a polished condition to establish the role of surface roughness on fatigue strength. The fatigue strength of each specimen was determined using a step test method. To establish a reference stress-life curve and to validate the step test method, fatigue tests were also conducted on a cold-rolled IN625 sheet having similar strengths as the AM specimens. Stress-life curves that include the influence of microstructure are estimated using the fatigue strength data and the reference stress-life curve from the wrought IN625. The fatigue fracture surfaces were characterized with SEM microscopy to determine the microstructure feature associated with fatigue crack nucleation and understand the variability of the fatigue results. Average roughness for all builds was measured to find trends with the high cycle fatigue results. Tensile test results for various mechanical properties including Young's modulus, yield strength, ultimate tensile strength and strain to failure z and xy specimens was plotted against fatigue strength to find trends. Fatigue strength was also evaluated against processing parameters to assess the influence and find optimal design parameters. Finally, mean stress correction methods for different R values were used to calculate average fatigue strength for designer specifications.