FRP Tank Helical Layer Unevenness Fatigue Strength
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Solution Overview
Problem
Conventional hydrogen storage tanks with fiber-reinforced plastic (FRP) layers experience reduced fatigue strength due to stepped portions on the surface of the helical layer, which affects the adjacent hoop layer, leading to structural bends and unevenness.
Innovation Solution
The tank design incorporates a liner with an FRP layer featuring hoop and helical layers, where at least one inner helical layer has a smaller fiber bundle sectional area than outer layers, reducing surface unevenness and transferring it to adjacent layers, thereby minimizing structural bends and enhancing fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional helical layer is formed with standard fiber bundle size, then the layer can be manufactured efficiently, but stepped portions occur on the surface causing reduced fatigue strength in adjacent hoop layers
Solution Approach 1:
The patent changes the physical parameter of fiber bundle sectional area in the helical layer. By using smaller fiber bundles (e.g., 1/2 or 1/3 of the standard size), the stepped portions on the helical layer surface are eliminated or reduced, preventing stress concentration and maintaining fatigue strength of adjacent hoop layers while preserving manufacturing efficiency
Solution Approach 2:
The patent applies local quality by using different fiber bundle sizes in different regions or layers. Specifically, inner helical layers use smaller fiber bundles to achieve smooth surfaces, while outer layers may use standard sizes, creating localized optimization without compromising overall structure
2Manufacturing precision
If fiber bundles in helical layer are wound in parallel with tank axis to eliminate space between bundles, then surface unevenness is reduced, but the winding process becomes fundamentally difficult and bends cannot be eliminated
Solution Approach 1:
Instead of changing the winding geometry (which would be fundamentally difficult), the patent changes the fiber bundle size parameter. By using smaller fiber bundles with standard winding angles, the same surface smoothness effect is achieved while maintaining ease of manufacture and standard winding processes
3Reliability
If the sectional area of fiber bundles in inner helical layers is reduced, then surface unevenness decreases and fatigue strength is preserved, but the fiber volume content ratio must be increased to maintain burst strength
Solution Approach 1:
The patent balances two opposing parameter requirements: reducing fiber bundle sectional area (affecting surface quality and fatigue strength) while increasing fiber volume content ratio (affecting burst strength). By carefully controlling both parameters, the patent achieves both fatigue strength preservation and burst strength maintenance
Solution Approach 2:
The patent applies local quality by using smaller fiber bundles specifically in inner helical layers where surface smoothness is most critical for preventing stress concentration in adjacent hoop layers, while maintaining or increasing overall fiber volume content to preserve burst strength of the entire tank structure
Data Source
AI summary
A tank that includes layers of fiber reinforced plastics (FRP) formed by alternately winding hoop and helical bundles of fiber over its outer surface. The winding produces stepped portions, i.e. unevenness, in a helical layer positioned as the innermost layer. Such unevenness affects an outer layer (especially a hoop layer) directly adjacent to the innermost helical layer and lowers fatigue strength of the adjacent outer layer. In order to prevent this fatigue strength decrease, the bundle of fiber used for the innermost helical layer has a smaller sectional area than the bundles used for the outer layers. Consequently, decreasing the sectional area of the innermost helical bundle decreases the stepped portions, which, in turn, decreases the transfer of unevenness to the outer layer (especially a hoop layer) directly adjacent to the helical layer. As a result, fatigue strength of the adjacent outer layer (especially a hoop layer) increases.