Case study: Evaluation of Bolted-On Stub Shaft

Location: Collector end at a terminal stud in a generator

Issue: A repair solution was proposed to salvage a generator with damage on the collector end by installing a bolted-on stub shaft  after severing the existing damaged shaft outboard

Objective: Verifying the potential impact on structural integrity by adopting the proposed mitigating strategy

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Background

  • A repair solution was proposed to salvage a generator with damage on the collector end by installing a bolted-on stub shaft  after severing the existing damaged shaft outboard.

  • Finite element analysis (FEA) was performed to evaluate the potential impacts on structural integrity by adopting proposed solution.

  • Mechanical loadings under considerations include bolt clamped force, torque exerted on shaft to overcome bearing friction, torque exerted on shaft to accelerate during startup and centrifugal force under full  operating speed. 

Summary of Analyses

  • The specified bolt tightening torque is calculated to be sufficient to ensure strong contact at flange interfaces.

  • Stress concentrations were found at the flange interface as a result of bolt pretension load. However, these stresses are compressive and relatively mild.

  • The stress in the bolt appears not excessive and should not pose potential threats to the integrity of bolted-on structure. 

  • The proposed modification is therefore recommended based on the predicted sufficient margin demonstrated by FEA analysis.

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