Oil-free turbomachinery relies on gas bearing supports for reduced power losses and enhanced rotordynamic stability. Gas foil bearings (GFBs) with bump-strip compliant layers can sustain large loads, static and dynamic, and provide damping to reduce shaft vibrations. The ultimate load capacity of GFBs depends on the material properties and configuration of the underlying bump strips structure. In high temperature applications thermal effects changing operating clearances and material properties can affect considerably the performance of the FB structure. The paper presents experiments conducted to estimate the nonlinear structural stiffness of a test FB for increasing shaft temperatures. A 38.17 mm inner diameter FB is mounted on a non-rotating hollow shaft affixed to a rigid structure. A cartridge heater inserted into the shaft provides a controllable heat source and thermocouples record temperatures on the shaft and FB housing. For increasing shaft temperatures (up to 188°C) a static load (ranging from 0 N to 133 N) is applied to the bearing and the deflection recorded. Load versus deflection tests render the FB static structural stiffness coefficient. In the test configuration, thermal expansion of the FB housing, larger than that of the shaft, nets a significant increase in bearing radial clearance which produces a significant reduction in the foil bearing structural stiffness. A simple physical model assembling individual bump stiffnesses predicts well the measured FB structural stiffness when accounting for variations with temperature of the bump elastic modulus and the actual radial clearance affected by the thermal growth of the shaft and bearing cartridge. Further tests identifying the FB structure dynamic stiffness and its equivalent viscous damping follow in a companion paper (Part II) for a similar range of shaft temperatures.

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