Flexure Bearing Analysis Procedures and Design Charts

Abstract

Flexure bearings are used in cryocooler compressors and expanders to maintain the ingegrity of the clearance seal between the piston and cylinder. At present, three-finger spiral flexure designs are widely used, but the tangential linear flexure design patented by The Aerospace Corporation is gradually being adopted by the industry.

In this study, analytical procedures were developed to predict flexure performance for any geometric configuration, considering complex flexure design requirements for operating amplitude, flexure radial and axial stiffnesses, fatigue stress allowables, and dynamic characteristics. Rotating a single flexure finger about the center of the drive shaft, a repeated multi-finger geometric model is generated. This model is then analyzed by a nonlinear finite- element analysis code, varying various geometric and material design parameters, to determine the impact of these parameters on flexure performance. The procedures to perform all analysis tasks have been automated. Results have also been verified with available test data.

A set of three-finger spiral flexure design charts was developed using these analysis procedures. The design charts provide basic design characteristics of the spiral flexures. The procedures and charts can be used for verification of design margins and effectiveness, for optimization of new designs with specified constraints, or for the design tangential flexures.