A comprehensive review on advancements in compliant structures of gas foil journal bearings

Gas foil journal bearings (GFJBs) are widely considered technically advanced bearings and a viable alternative to conventional rolling element and oil-lubricated bearings in high-speed rotating machinery. GFJBs offer advantages such as reduced maintenance, improved efficiency, and the ability to operate in challenging environments. A traditional GFJB consists of (i) a smooth top foil for the generation of hydrodynamic pressure, (ii) a compliant corrugated foil beneath the top foil for tailoring stiffness, and (iii) a bearing base to hold the foils together. The shape and geometry of corrugated thin foil are primarily designed for the essential stiffness and load-carrying capacity of the bearings. The thickness of thin foils is in the range of 100–150 μm. The fabrication of complaint thin foils to their desired shapes and sizes is quite challenging. Engineers and researchers around the world have designed and published various advanced design structures of GFJBs to improve their static and dynamic characteristics. The corrugated or compliant structure is the most significant component of GFJBs from design and fabrication point of view. Therefore, a modest attempt is made by the authors to review and report systematically on various foil journal bearings reported in open literature. The study covers four primary categories, which are centered around the design of compliant structures, materials, manufacturing processes, and coatings over the years. By analyzing the state-of-the-art advancements, this review aims to identify key areas for further research, explain technological trends, and underline the pivotal role of GFJBs in various high-speed applications across industries.