Repairing Uneven Bond Surfaces in Composite Sandwich Structures
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Solution Overview
Problem
Existing methods for repairing damaged honeycomb composite structures in composite sandwich structures, such as those used in gas turbine engines, face challenges in achieving strong bonding between replacement honeycombs and uneven laminate surfaces, as adhesive bond strength declines with increased thickness and cannot effectively absorb surface irregularities.
Innovation Solution
A method involving the separation of the face sheet and original honeycomb from the skin, thinning the uneven bond surface to create a more even surface, applying a conformable layer and adhesives, and pressing a replacement honeycomb into this layer, followed by curing to restore the component structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If additional thickness of adhesive is used to absorb the unevenness of the dimpled imprints, then the bonding between replacement honeycomb and laminate is improved, but adhesive bond strength rapidly declines as thickness increases
Solution Approach 1:
The patent applies preliminary action by thinning the uneven bond surface before applying adhesive. The method involves removing material from high spots on the dimpled imprint surface to create a flatter substrate, then applying a conformable layer that can still accommodate remaining irregularities. This preliminary surface preparation allows for thinner adhesive application while maintaining bond strength.
Solution Approach 2:
The patent changes the physical parameters of the bonding interface by introducing a conformable layer with specific properties (thickness, compliance, adhesion). This layer has parameters optimized to bridge the gap between uneven substrate and flat honeycomb face, providing mechanical compliance while maintaining strong chemical bonds to both surfaces.
2Stability of the object's composition
If the ends of the replacement honeycomb are made to align perfectly with the dimpled imprints, then the structural integrity is improved, but this is unfeasible due to surface unevenness
Solution Approach 1:
The patent introduces a conformable layer as an intermediary between the uneven laminate surface and the flat replacement honeycomb face. This intermediate layer absorbs the misalignment and surface irregularities, allowing the honeycomb to be positioned correctly without requiring perfect alignment with the dimpled imprints, thus maintaining structural integrity while simplifying the manufacturing process.
Solution Approach 2:
The conformable layer functions as a flexible thin film that can deform to match the uneven substrate surface while presenting a flat bonding surface to the honeycomb. This flexible intermediate layer accommodates the geometric incompatibility between the dimpled imprint and flat honeycomb face, making alignment feasible without compromising structural integrity.
3Manufacturing precision
If the honeycomb is machined to have a flat surface, then the manufacturing precision is improved, but the flat surfaces do not conform well with uneven surfaces without crushing the honeycomb
Solution Approach 1:
The conformable layer serves as a mediator that allows the use of precisely machined flat honeycomb surfaces without requiring the underlying substrate to be equally precise. The compliant intermediate layer absorbs the surface mismatches, preventing stress concentrations that would otherwise crush the honeycomb structure while maintaining the benefits of precision-machined honeycomb faces.
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 method provides a structurally durable repair by reducing surface variation, allowing for a stronger bond between the replacement honeycomb and the laminate, maintaining the original dimensions and structural integrity of the composite sandwich structure.
Implementation Method 1
adhesives to bond the repair section to itself and the adjacent areas
Data Source
Figure 1~3
Figure 4~5
AI summary
A method of restoring a section of a component (20) having a honeycomb (26) bonded to a skin (24) includes the steps of separating a first honeycomb (26) from the skin (24), wherein the skin (24) includes an uneven surface. At least a portion of the uneven surface (24) is removed to form a bonding surface (47) on the skin (24). A conformable layer (66) is bonded to the bonding surface (47). Then a replacement honeycomb (26') is then bonded to the conformable layer (66).