Composite Sandwich Shell Edge Joint with Barrel Nuts
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Solution Overview
Problem
Conventional joint designs for composite sandwich shell edges are inefficient in weight and prone to stress due to ductility issues in composites, limited bearing capability, and thermal expansion mismatches, leading to additional weight penalties and manufacturing costs.
Innovation Solution
A combination bonded and mechanically-fastened joint configuration using outboard and inboard buildup pads, bridging plies, and barrel nuts, which minimizes bending loads and avoids the need for drilling precision holes, allowing for efficient load transfer and thermal expansion management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional metal joint members are used with composite sandwich shells, then mechanical fastening is achieved, but weight efficiency deteriorates due to additional reinforcement requirements
Solution Approach 1:
The joint structure uses composite materials throughout - composite sandwich shell edges, composite buildup pads, and composite barrel nuts. This eliminates the need for metal joint members and reduces weight by avoiding the reinforcement requirements that metal fasteners impose on composite structures.
Solution Approach 2:
The invention replaces conventional metal mechanical fastening systems with composite barrel nuts that are mechanically attached to composite buildup pads. This substitution eliminates the need for metal-to-composite interfaces and the associated reinforcement requirements, reducing overall joint weight.
2Ease of manufacture
If thick solid laminates are used at shell edges to enable conventional metal fastening, then mechanical attachment is achieved, but manufacturing cost and complexity increase due to drilling close tolerance holes
Solution Approach 1:
The buildup pads are constructed from composite materials (solid laminates or sandwich construction) that can be mechanically attached using composite barrel nuts. This eliminates the need to drill close tolerance holes in the primary shell structure, reducing manufacturing complexity while maintaining fastening capability.
Solution Approach 2:
The joint is segmented into separate components: the shell edge, buildup pads, and barrel nuts. This allows the buildup pads to be independently fabricated and attached to the shell, avoiding the need to modify the primary shell structure with precision holes and reducing overall manufacturing complexity.
3Force
If asymmetrical flange configuration is used in sandwich edge joints, then load transfer is achieved, but additional bending loads are imposed on the adjacent shell requiring local reinforcement
Solution Approach 1:
The invention acknowledges the inherent asymmetry in sandwich edge joints but manages it through proper design of the buildup pads and barrel nut configuration. The asymmetrical flange configuration is optimized to minimize bending moments while maintaining effective load transfer, reducing the need for additional shell reinforcement.
4Ease of manufacture
If metal joint elements are used with composite structures, then mechanical fastening is achieved, but thermal expansion mismatch creates additional stresses requiring reinforcement
Solution Approach 1:
The joint structure uses homogeneous composite materials throughout - composite shell edges, composite buildup pads, and composite barrel nuts. This material homogeneity ensures matched thermal expansion coefficients, eliminating thermal expansion mismatch stresses that would occur with metal-to-composite interfaces.
Data Source
AI summary
A composite sandwich shell edge joint includes an outboard buildup pad, an inboard buildup pad spaced-apart and adjacent to the outboard buildup pad, an outboard face sheet extending from the outboard buildup pad, an inboard face sheet extending from the inboard buildup pad, bridging plies connecting the outboard buildup pad and the inboard buildup pad and at least one barrel nut installed in the buildup pads.