Bending fatigue behaviour of direct metal laser sintering (DMLS), Nickel (Ni) Alloy 718 has been assessed as preliminary qualification to additively manufacture advanced gas turbine engine components. Motivation for this work comes from the possibility of using DMLS to improve functionality of hot‐section components. By using DMLS, turbine blades and heat exchangers cooling passages can be enhanced, leading to improved engine performance. This study focuses on vibratory high cycle fatigue (HCF) assessment of DMLS Ni Alloy 718 from two suppliers. Specimens were fatigued via vibration‐based bending and compared with published rotating bending cold‐rolled Ni Alloy 718. Tensile analysis and microscopy were also conducted to understand fatigue and fracture trends. HCF, tensile properties and microscopy comparisons show that fatigue and strength of DMLS Ni may be sensitive to post‐fusion treatments. Nonetheless, fatigue performance of DMLS Ni compares well with rotating bending fatigue of cold‐rolled Ni.

An experimental procedure for qualifying material properties from cyclically worked parts was investigated in support of aging gas turbine engines and digital twin initiatives. For aging components, remanufacturing or repair efforts are necessary to sustain the life cycles of engines; and for digital twin, the virtual representation of a part requires accurate geometric and component material property measurement. Therefore, having an effective, non-destructive way to assess the material performance of parts is necessary. Since low cycle, low strain, mechanical testing is the ideal experimental approach for non-destructively assessing material properties, investigating the accuracy and trends of tensile properties of fatigue loaded parts was important. The fatigued parts used for this study were specimens tested according to the George Fatigue Method, and the materials observed were cold-rolled Inconel Alloys 625 and 718, and direct metal laser sintering (DMLS) Nickel Alloy 718. The tensile material properties were compared against pristine (non-fatigued) and published data. The comparison for the cold-rolled 625 and 718 results show an increase and a decrease, depending on rolling direction, of tensile strength due to the effects of fatigue cycles; however, the variation of the vibration affected tensile properties are all within one standard deviation of the pristine data. The comparisons of DMLS Nickel Alloys was conducted against two sets of alloys from different suppliers, and the results showed that the tensile properties are sensitive to DMLS manufacturing parameters and post-sintering processes. A digital twin related, nondestructive, material property determination technique is also discussed in this manuscript. The true alloy density was determined with the water displacement method, and elastic modulus is determined with an iterative Ritz method model. The modulus is under-predicted with this method, but suggestions for improving the model are discussed.

An additive manufacturing (AM) process has been used to fabricate beam components with unique internal geometries capable of reducing weight and inherently suppressing vibration of the structure. Using the laser powder bed fusion (LPBF) AM process, four unique designs are investigated to quantify and understand the damping effectiveness of this manufacturing concept. Forced-response tests are conducted to validate the damping capability of each internal design configuration. The effects of external geometry, thermal distribution associated with internal friction, strain amplitude, and loading rate dependence on damping performance are studied. The results of the studied beams are compared to the damping performance of a fully-fused, or solid baseline LPBF beam. With only 1–4% internal beam volume alteration, the four unique beams are capable of providing up to ten times damping into their respective systems compared to the baseline, solid beam. From the studies of different parameter effects on damping, the main mechanism for vibration suppression is identified. Validation of the vibration suppression physics allows for internal feature optimization via LPBF that can maximize damping effectiveness.

This study observes coaxing effects on aerospace nickel alloys during vibration-based bending fatigue loading. The purpose of this analysis is to determine if Goodman diagrams can be constructed using bending fatigue life data at experimentally defined cycles to failure. The methodology for controlling the number of cycles to failure requires a series of understressing steps, where stress amplitude is incrementally increased at each step. This method, known as the step-test procedure, states that, for some materials, the stress amplitude corresponding to the controlled cycles-to-failure can be determined through linear interpolation between the failure step and the previous non-failure step. Using the step-test procedure, experimental bending fatigue life results were gathered from cold-rolled Inconel 625 and 718 plate specimens. These bending loads are applied with a vibration-based experimental method, known as the George fatigue method, which utilizes modal vibration for fatigue loading. The fatigue life results from the George fatigue method are compared to life data from previously published constant stress amplitude experiments to determine if coaxing affects the fatigue performance of the Inconel materials. Results show that Inconel 625 has an improved fatigue performance that could be attributed to several possible factors, including coaxing, while the Inconel 718 data is shown to be within a 50% confidence band of constant stress amplitude data from the same material stock. The findings in this study increases the knowledge necessary to attain more relevant and less conservative empirical data for designing against high cycle fatigue (HCF) failure of complex gas turbine engine components.

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