Fan Case Bolt Hole Bushing Adhesive Shim Alignment
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Solution Overview
Problem
In gas turbine engine fan assemblies, maintaining precise control over bolt hole alignment and size is challenging, especially when using composite materials, as it requires tight tolerances to distribute shear loads effectively, and press-fitting bushings can cause local cracking.
Innovation Solution
The use of bushings with an outer diameter less than the bolt hole inner diameter, accompanied by an adhesive material forming a liquid shim between the bushing and the bolt hole, allowing for looser tolerances while maintaining alignment and load distribution without direct contact, which reduces the risk of cracking in composite materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If bushings are press fit into bolt holes through composite material fan case, then shear load transfer is achieved, but local cracking occurs that compromises fan case integrity
Solution Approach 1:
The patent introduces an intermediary substance (adhesive material or liquid shim) between the bushing and the composite fan case material. This intermediary layer allows the bushing to be installed without direct mechanical contact that would cause cracking, while still enabling effective shear load transfer from the bushing to the fan case through the adhesive bonding.
2Strength
If tight tolerances are used for bolt hole alignment in fan case, then shear load distribution is improved, but manufacturing complexity and difficulty increase
Solution Approach 1:
The patent changes the physical state and properties of the bonding interface by using adhesive material or liquid shim. This allows the system to accommodate larger dimensional variations and misalignments in the bolt holes while still achieving proper load distribution, effectively relaxing the manufacturing tolerance requirements without sacrificing structural performance.
3Measurement precision
If bushing outer diameter is made equal to bolt hole inner diameter for tight fit, then alignment precision is improved, but risk of cracking in composite material increases
Solution Approach 1:
The adhesive material or liquid shim serves as a mediator that decouples the alignment function from the mechanical fit function. The bushing can have a larger outer diameter that provides good alignment, while the adhesive layer fills the gap and provides the necessary mechanical bonding without creating stress concentrations that would cause cracking in the composite material.
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
This solution enables secure fastening and effective shear load transfer with reduced risk of component failure due to fatigue or cracking, allowing for the use of looser tolerances in bolt hole fabrication and ensuring proper alignment of bushings within the fan case.
Implementation Method 1
an adhesive material disposed within each annular gap between one of the plurality of bushings and the corresponding one of the plurality of fan case bolt holes, wherein the adhesive material forms a liquid shim separating the bushing outer surface from the bolt hole inner surface
Data Source
AI summary
In a fan case having an annular outer wall with a plurality of fan case bolt holes there through, bushings are inserted into the fan case bolt hole and are dimensioned to define an annular gap between the bolt hole inner surface and the bushing outer surface. An adhesive material disposed within each annular gap between the bushing and the corresponding fan case bolt hole, with the adhesive material forming a liquid shim separating the bushing outer surface from the bolt hole inner surface.