The fatigue life behavior and internal wall erosion of inherently damped additive manufacturing (AM) specimens subjected to vibration bending are under investigation. This study originated in support of research that demonstrated 95% strain amplitude reduction due to damping capability of AM components with 1-3% internal volume of unfused powder. The demonstration of the damping capability has been carried out using several laser powder bed fusion (LPBF) specimens of various thicknesses, lengths, and unfused internal powder configurations. In addition, the capability has been demonstrated on both nickel-based alloys and steel specimens. Despite the promising inherent damping capability of the AM design method versus a fully-fused components, the damping mechanism of unfused powder motion raises structural integrity concerns that may hinder its viability as a future design application. The main concern is in regards to the interaction of powder particles and the interior walls of the inherently damped specimen during vibration loading. In other words, the inquiry of whether erosion of the interior walls of components will create local stress concentrations that will affect fatigue life of a component during operation has been presented. The following effort aims to explore the structural integrity concern of inherent damping components by comparing vibration bending fatigue life of unfused powder pocket and fully-fused nickel based alloy 718 specimens manufactured via the LPBF process. For this study, both the United States Air Force Developed hybrid-plate vibration bending fatigue and conventional vibration bending fatigue test methods will be explored. The latter of the two fatigue testing methods (the conventional) will mainly address how much the unfused powder interaction suppresses vibration during fatigue to failure. Also addressed in this study is how much erosion due to unfused powder interaction will occur on the interior walls of specimens during vibration fatigue testing. Specifically, measuring the wall thicknesses of cyclically loaded unfused powder pocket specimens and compared against pristine unfused powder pocket samples is necessary to understand erosion. Based on previous research efforts in this area, it is anticipated that the results for fully-fused and unfused powder pocket specimens are going to show comparable fatigue behaviors. It is also believed that erosion will be present along the interior walls; the presence of a galling phenomenon from high friction or elevated temperature interaction of powder is also expected. Nonetheless, the existence of porous features consistent with stock LPBF process parameters as well as high stress amplitudes towards the surface of the specimen will prove to be the dominating factor in crack initiation for fatigue failure.


Vibration Fatigue Assessment of Additive Manufactured Nickel Alloy With Inherent Damping

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

Turbo Expo - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.