Resources / Publications
Erik Nyberg (1), Dídac Llopart i Cervelló (1), Ichiro Minami (1)
Aerospace, 8, Issue 3, March 2021: 75. DOI: 10.3390/aerospace8030075
tribotesting; starved lubrication; cryogenic lubrication; space-tribology; COTS; X-ray microtomography; computed tomography; XMT; CT-scan; lab-to-field upscaling
Liquid lubricants are critical to enable long-life operation of high-performance machinery, such as geared actuators employed in robotics. In space applications, actuator gearboxes must operate in low temperatures, where liquid lubricants face inherent problems related to low temperature rheology. Heaters are relied upon to provide acceptable gearbox temperatures. Unfortunately, heating is energy-intense and does not scale well with increasing mechanism mass and performance. Effective boundary lubrication (BL), on the other hand, can minimize problems of low temperature rheology. BL relies on tribofilm formation over conventional fluid film separation. Effective space grade boundary lubricants can potentially allow for drastically reduced amounts of oil and the accompanying rheological problems. In this work, we describe the design of a methodology to evaluate and analyze tribology of actuator gearboxes operated under cryogenic oil-starved conditions in N2 atmosphere. The devised methodology enables research pertinent to space actuator tribology by accelerated testing and advanced analysis, as demonstrated by a lubricant candidate case study. Complementary microscopy techniques are discussed, and a novel methodology devised for gear internal microstructure analysis by X-ray microtomography (XMT) is presented.
Dragonfly was used to export cross-sectional images at every resolved voxel layer to produce a sequence of images (tiff-stack).
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