Composite Joint Design for Cryotank Weight and Leak Reduction
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Solution Overview
Problem
Composite tanks, such as cryotanks, face issues with weight and leak paths due to conventional joint designs, which affect payload capacity and fuel efficiency in vehicles and spacecraft, and are prone to delamination under load.
Innovation Solution
A composite joint design featuring a curved wall with blind holes and oversized coarse threads for shear fittings, combined with bolts and washers, secures a cap over an opening, minimizing leak paths and delamination risks while optimizing weight and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If conventional joint designs are used in composite tanks, then the joint can be manufactured with standard methods, but the tank weight increases and fuel efficiency decreases
Solution Approach 1:
The shear fitting is nested within the composite wall structure, with threads formed inside blind holes that are countersunk into the wall. The cap members nest over the opening and engage with the shear fittings through threaded holes, creating a compact integrated joint that eliminates external fasteners and reduces overall tank weight while maintaining manufacturability
Solution Approach 2:
The joint components including the shear fittings, cap members, and the wall itself are constructed using composite materials. The shear fittings feature threads formed in composite material with specific fiber orientations (0°, 45°, 90°) to optimize strength-to-weight ratio, allowing the tank to achieve weight reduction while maintaining structural integrity and ease of manufacture through standardized composite processing techniques
2Reliability
If conventional joint designs are used in composite tanks, then the joint can be assembled with standard components, but the number of leak paths increases
Solution Approach 1:
The design extracts and eliminates traditional penetration-style fasteners that create multiple leak paths through the tank wall. Instead, the shear fittings are threaded into blind holes that are countersunk, and the cap members engage through threaded holes that do not penetrate the entire wall thickness, thereby removing unnecessary leak paths while maintaining a relatively simple joint structure
Solution Approach 2:
The joint is segmented into distinct functional components: shear fittings embedded in the wall, cap members covering the opening, and threaded engagement interfaces. This segmentation allows each component to be optimized for its specific function while reducing the overall complexity of the joint structure and minimizing the number of interfaces where leaks could occur
3Strength
If standard thread designs are used in composite walls, then the joint can be manufactured with standard tools, but delamination occurs under load
Solution Approach 1:
The thread design incorporates local quality variations with different fiber orientations at different angular positions within the composite wall. Specifically, 0° fibers provide axial strength, 45° fibers provide shear strength, and 90° fibers provide transverse strength. This localized optimization of fiber orientation at the thread interface prevents delamination under load while maintaining compatibility with standard thread formation tools and manufacturing processes
Solution Approach 2:
The invention changes the parameters of thread formation by using oversized coarse threads with specific pitch and diameter ratios, and by forming threads in composite material with controlled fiber orientations rather than traditional metal materials. This allows the joint to achieve higher strength while preventing delamination, and can be manufactured with adapted standard tools rather than requiring entirely new manufacturing processes
4Strength
If more fasteners are used to secure the cap, then the joint strength increases, but the weight of the tank increases
Solution Approach 1:
Both the shear fittings and cap members are constructed from composite materials with optimized fiber orientations, providing high strength-to-weight ratio. This allows the joint to achieve the required strength with fewer and lighter fasteners compared to traditional metal fastener designs, thereby reducing overall tank weight while maintaining joint strength
Data Source
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AI summary
A method, a composite joint, and a composite tank are presented. The composite tank comprises a curved wall, a plurality of shear fittings, and a plurality of bolts. The curved wall has an opening. The plurality of shear fittings is threaded into a plurality of blind holes in the curved wall around the opening. The plurality of bolts engages the plurality of shear fittings and joins a cap to the curved wall.