The Steady Performance of Complaint-surface Aerostatic Thrust Bearings

Abstract

The object of the research is to predict and confirm the predicted steady performance of aerostatic compliant surface thrust bearings. The use of a compressible lubricant (air) instead of an incompressible lubricant (oil) forms a natural extension of previous work on hydrostatic bearings [201] to [205]. The design of the main experimental apparatus was assisted by the theory of Dowson and Taylor[201] modified for compressible lubricants. A subsidiary experimental apparatus to determine the bulk modulus of the elastomers to be used was also constructed, and the design was similar in principle of operation to one described by Rightmire [305]. Experiments were first performed on rigid bearings to develop the rig. A method of predicting load capacity was developed which was considerably simpler than previous theory [108]. The theory lines agreed well with the experiments if the experimentally determined discharge coefficient and the roughness of bearing surfaces are taken into account. Experimental determination of elastomer properties, i.e. bulk modulus and elastic modulus, indicated that the former is several orders of magnitude larger than the latter. This means that the Poisson's ratio of these elastomers is very close to 0.5 and the governing elastic equations, obtained by extending Dowson's theory, had to be modified further to account for nearly incompressible or completely incompressible elastomers. A mathematical model has therefore been established, and an attempt has been made to solve the equations by finite difference methods. The performance of various elastomers bonded to one rigid surface with varying aspect ratio and hardness was compared with the performance of unbonded elastomers and to rigid bearing performance. It was discovered that the unbonded elastomers have inferior performance to bonded ones, but they are superior to rigid bearings, and they also have advantages such as quick removal and easy exchange of damaged compliant layers.