Fluted Core Sandwich Panel Joining with Stiffener Insert
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Solution Overview
Problem
Existing methods for joining sandwich truss core panels, especially curved panels, face challenges in accommodating variations in panel end positions and flute alignment, leading to suboptimal shear and stiffness capabilities in the final joint, particularly in large composite structures that exceed autoclave equipment size limits.
Innovation Solution
A method involving the alteration of panel ends by ramping facesheets and trimming fluted cores to form inter-panel gaps, where a pre-cured core stiffener insert with flanges and web configuration is used to align and bond the panels, accompanied by scarf splices, allowing for variations in flute alignment and reducing the need for local pad-ups and fasteners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pre-cured sandwich panels with fluted truss cores are joined using adhesively bonded scarf joints, then large composite structures can be fabricated outside autoclave equipment, but variations in flute alignment at panel joints reduce shear and stiffness capability
Solution Approach 1:
A temporary positioning device (TPD) is introduced as an intermediary element between panel ends during assembly. The TPD includes positioning blocks that fit into recesses in the panel ends, precisely locating the last panel end relative to the joint centerline before adhesive bonding. This mediator compensates for cumulative tolerance variations and ensures accurate flute alignment without requiring tight manufacturing tolerances on the panels themselves.
Solution Approach 2:
The panel ends are pre-prepared with recesses and positioning features before final assembly. The TPD is pre-configured with positioning blocks that correspond to these recesses. This preliminary preparation allows for quick and accurate positioning during assembly, ensuring proper flute alignment without requiring complex adjustment procedures during the bonding process.
2Reliability
If strict flute matching is required at panel joints, then shear and stiffness capability is maintained, but manufacturing complexity and time increase significantly
Solution Approach 1:
The TPD serves as a temporary intermediary that simplifies the manufacturing process by providing mechanical positioning guidance. Instead of requiring complex measurement and adjustment procedures to achieve flute alignment, the positioning blocks in the TPD guide the panel ends into correct alignment automatically, reducing manufacturing complexity while ensuring reliable joint performance.
Solution Approach 2:
The positioning blocks and recesses are designed to self-align the panel ends during assembly. The geometry of the positioning features automatically guides the panels into the correct position without requiring external measurement or adjustment, allowing the assembly process to self-correct tolerance accumulations and simplify manufacturing procedures.
3Reliability
If the position of the final core flute varies from the joint centerline, then the desired shear and stiffness capability cannot be maintained, but adjusting panel positions during assembly increases fabrication time
Solution Approach 1:
The TPD is prepared in advance with positioning blocks that correspond to recesses in the panel ends. During assembly, the panels are simply placed onto the TPD, which automatically positions the last panel end correctly relative to the joint centerline. This preliminary preparation eliminates the need for time-consuming measurement and adjustment operations during assembly, maintaining reliable flute alignment while reducing fabrication time.
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 enables the formation of joints with maintained shear and stiffness capabilities, reduces weight and fabrication time, and simplifies the fit-up process by accommodating various alignment conditions, making it a cost-effective and repeatable out-of-autoclave process.
Implementation Method 1
placing a layer of adhesive film over the ramped portions and the flanges
Data Source
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AI summary
Fluted core sandwich panels are joined together to form a composite structure. Variations in panel ends are accommodated by a core stiffener insert installed in a joint between ends of the panels.