Multi-Piece Bushing Assembly for Lower Hole Stress Concentration
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Solution Overview
Problem
Structures with openings or holes are prone to failure due to local stress concentrations, and bushings used to couple these structures can also fail under load, causing damage to both the bushing and the fastener.
Innovation Solution
A multi-piece bushing assembly is designed with a tubular component and a ring, where the tubular component is cold expanded into the structure and the ring is coupled via a pressure fit, creating a residual compressive stress layer and eliminating the need for an undercut shoulder, thereby reducing local stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-piece bushing is used, then the structure is simple and manufacturing is easier, but local stress concentrations occur at the shoulder and flange areas leading to bushing failure
Solution Approach 1:
The bushing is divided into multiple discrete components: a tubular component and a flanged component. This segmentation eliminates the continuous shoulder geometry that causes stress concentrations in single-piece bushings, as each component can be optimized independently and the joint between components creates a different stress distribution pattern.
Solution Approach 2:
The invention uses composite construction by cold expanding the tubular component onto the flanged component, creating a metallurgical bond that combines the advantages of both components while distributing stresses across the interface rather than concentrating them at a sharp shoulder transition.
2Ease of manufacture
If a traditional bushing with undercut shoulder is used, then the bushing can be installed, but additional machining is required increasing manufacturing complexity and cost
Solution Approach 1:
By segmenting the bushing into separate tubular and flanged components that are cold-expanded together, the design eliminates the need for undercut shoulders or complex machining features. The components can be manufactured using standard processes and assembled through cold expansion, reducing overall manufacturing complexity.
Solution Approach 2:
The invention changes the installation method from mechanical machining (undercut shoulders) to a cold expansion process. This parameter change in the installation approach eliminates the need for additional machining operations while ensuring proper fit and stress distribution.
3Reliability
If a bushing is used to protect openings from stress concentrations, then the structure is protected, but the bushing itself becomes susceptible to failure at stress concentration points
Solution Approach 1:
Segmenting the bushing eliminates the continuous stress path through a sharp shoulder, breaking the stress flow into discrete segments. This prevents the development of high stress concentrations at the shoulder-root intersection that would otherwise propagate through the entire bushing structure.
Solution Approach 2:
The cold-expanded composite construction creates a reinforced interface between components where the expansion process generates compressive residual stresses that counteract applied loads, effectively strengthening the joint area against failure while maintaining protection of the opening.
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
The multi-piece bushing assembly effectively reduces local stress concentrations, increases fatigue strength, and eliminates the need for additional machining, enhancing the reliability of the fastening assembly under loaded conditions.
Implementation Method 1
The first component is cold expanded into the structure and the second component
Implementation Method 2
creating a residual compressive stress layer
Implementation Method 3
the first component and the second component being formed as discrete components of the bushing assembly. The first component is coupled to the second component via a pressure fit
Data Source
AI summary
A bushing assembly for a structure having a first aperture is provided. The bushing assembly includes a first component configured to be received by the first aperture and having a second aperture. A maximum width of the first component defines an outer diameter. The bushing assembly further includes a second component positioned outside of the first aperture and coupled to the first component, the second component having a third aperture extending through the second component. The third aperture is dimensioned so as to be equivalent to the outer diameter of the first component, and the first component and the second component are formed as discrete components of the bushing assembly.