Fiber Reinforced Composite Stepped Surface Fabrication
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Solution Overview
Problem
Fiber reinforced composite structures with stepped or curved surfaces face issues due to fiber bridging over tooling features, leading to incomplete compaction and reduced mechanical performance, as stiff fibers resist conforming to uneven surfaces.
Innovation Solution
The method involves laying up fiber reinforced material plies in a fixed axis rosette pattern over a tool with a curved stepped surface, forming slits in areas where bridging occurs, and consolidating the plies with additional orientations beyond conventional 0, 90, +/-45 degrees to ensure homogeneous properties and prevent fiber bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If stiff fibers are used to achieve high mechanical properties, then the mechanical performance is improved, but the fibers cannot conform to tooling features such as stepped surfaces, resulting in incomplete compaction
Solution Approach 1:
The continuous fibers are segmented by forming slits in the plies at locations where fiber bridging occurs. This segmentation allows the fiber ends to be pulled into the stepped features during compaction, ensuring complete consolidation while maintaining the high strength benefits of stiff fibers in the compacted regions.
Solution Approach 2:
Slits are formed locally at specific positions where fiber bridging occurs over stepped tooling features, rather than uniformly across the entire ply. This localized modification allows fibers to conform to tooling features at critical areas while maintaining the overall structural integrity and mechanical properties of the composite.
2Ease of manufacture
If fibers are allowed to bridge over tooling features, then the layup process is simpler, but the plies are not fully compacted, reducing laminate performance
Solution Approach 1:
Slits are formed in the plies before the compaction process begins, at locations where fiber bridging is anticipated to occur. This preliminary action prepares the fiber structure in advance, allowing the fibers to be pulled into the stepped features during compaction without requiring complex real-time adjustments to the layup process.
3Ease of manufacture
If conventional ply orientations (0, 90, +/-45 degrees) are used, then the manufacturing process is standard, but the off-axis properties and homogeneity are insufficient
Solution Approach 1:
The ply orientations are arranged in a fixed axis rosette pattern with asymmetric angular spacing rather than conventional symmetric stacking. This asymmetric arrangement, with plies oriented at specific angles relative to a fixed axis, creates a more homogeneous distribution of fiber directions throughout the laminate, improving off-axis properties while maintaining manufacturability.
Data Source
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AI summary
Fiber reinforced composite structures having curved stepped surfaces are fabricated by laying up plies (38) of fiber reinforced material over a tool having a stepped tool feature. The plies (38) are rotated about a fixed axis as they are laid up to substantially form a fixed axis rosette pattern. The plies are angularly oriented such that at least certain of the plies have fiber orientations (52) other than 0, +45, -45 and 90 degrees. Potential bridging of the fibers over the stepped tool features is reduced or eliminated by cutting slits (42) in the plies in the area of the stepped features, so that the plies can be fully compacted.