Threaded Spool Shaft Compliance Profile for Stress Redistribution
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Solution Overview
Problem
In rotating machinery, stress is concentrated at threaded connections, leading to fatigue and material degradation, particularly in highly loaded components, which can initiate cracks and require repair, and existing solutions add complexity or mass.
Innovation Solution
A stress redistribution system for threaded connections in rotating machinery, featuring a hollow shaft with a contoured inner surface that redistributes stress by increasing compliance at the loaded end and reducing it at the unloaded end, using a threaded fastener to apply compressive and tensile loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high axial clamp loads are used to connect components, then the connection strength is improved, but stress concentration at threaded connections increases leading to fatigue
Solution Approach 1:
The shaft wall thickness is varied locally along its length, being thinner at the loaded end and thicker at the unloaded end. This non-uniform thickness distribution creates different compliance characteristics at different locations, allowing the connection to maintain high clamp loads while redistributing stress to reduce fatigue at critical threaded connection points.
2Reliability
If stress is concentrated at threaded connections to maintain connection integrity, then connection reliability is improved, but fatigue initiation increases requiring repair
Solution Approach 1:
The shaft geometry is modified by changing the wall thickness parameter along its length. This parameter change creates a compliance gradient that redistributes the stress distribution along the threaded connection, reducing peak stresses that lead to fatigue initiation and extending the service life before repair is needed.
3Ease of manufacture
If conventional threaded connections are used with uniform shaft thickness, then manufacturing simplicity is maintained, but stress redistribution is insufficient leading to fatigue
Solution Approach 1:
The shaft is designed with non-uniform wall thickness, creating local variations in compliance along its length. This local quality variation enables stress redistribution without adding complex external components, maintaining manufacturing simplicity while significantly improving fatigue life through optimized stress distribution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Redistributes stress to prevent fatigue initiation and extend the service life of threaded connections by balancing load distribution among threads, without adding mass or complexity.
Implementation Method 1
The inner surface has a contour so that the wall has one thickness at the loaded end and another greater thickness at the unloaded end so that the wall has more compliance at the loaded end as compared to at the unloaded end. The compliance operates to reduce stress resulting from the load at the loaded end and to redistribute stress throughout the threaded connection.
Data Source
AI summary
Systems provide load redistribution and reduced stress at otherwise highly loaded threads. A system for a threaded connection includes a shaft that rotates about an axis. The shaft is a hollow cylinder with an inner surface and a wall defined around the inner surface. A fastener is in threaded engagement with the shaft. The fastener applies a compressive load holding the shaft under a tensile load. The threaded connection extends from a loaded end adjacent a place of application of the compressive load, to an unloaded end opposite the loaded end. The inner surface has a contour, and the wall has one thickness at the loaded end and another greater thickness at the unloaded end, so the wall has more compliance at the loaded end as compared to at the unloaded end to reduce a stress resulting from the load and redistributing stress throughout the threaded connection.