Composite Ply Stacking Sequence for Wrinkle-Free Forming
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Solution Overview
Problem
Existing methods for forming composite articles on tools with curved or uneven surfaces often result in wrinkles, particularly at bevels or protrusions, due to the difficulty in conforming prepreg stacks without air trapping and fiber orientation issues.
Innovation Solution
A method involving a specific stacking sequence of prepreg plies with fibers oriented at 0°, 90°, 45°, and 135° angles, where plies with orthogonal fibers are arranged closest to the tool and forming medium, and diagonal fibers are placed between them, allowing for sliding and reducing shearing forces that cause wrinkles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a vacuum bag is used to conform the stack to the tool, then the stack can be pressed against curved surfaces, but wrinkles form at bevels and protrusions
Solution Approach 1:
The invention changes the fiber orientation parameters in the ply stack by placing plies with fibers at different angles (0°, 90°, 45°, 135°) in specific sequences. This parameter change allows the stack to better accommodate curved and beveled tool surfaces without wrinkling, as the varied fiber directions distribute stresses more evenly during vacuum bag forming.
Solution Approach 2:
The invention uses a composite stacking sequence combining plies with fibers in different orientations (0°, 90°, 45°, 135°) to create a multi-directional fiber architecture. This composite structure enables the material to handle complex tool geometries including bevels and protrusions without forming wrinkles, as each fiber direction contributes to stress distribution in different planes.
2Device complexity
If plies are stacked with fibers in the same direction, then the structure is simple, but wrinkles form during forming on tools with complex geometries
Solution Approach 1:
The invention introduces parameter changes by varying the fiber orientation angles in the ply stacking sequence. Instead of using uniform fiber directions, the patent specifies a pattern including 0°, 90°, 45°, and 135° orientations. This increases stacking sequence complexity but eliminates wrinkles on complex tool geometries by distributing mechanical stresses across multiple fiber directions.
3Strength
If the tool has bevels or protrusions to create thickened regions, then reinforcement is achieved, but wrinkles form in the flanges
Solution Approach 1:
The invention applies local quality by using plies with specific fiber orientations in specific locations within the stack. The stacking sequence is designed so that certain fiber directions are positioned to handle stresses in flange areas while other directions provide reinforcement in thickened regions. This localized optimization of fiber orientation prevents wrinkles in flanges while maintaining reinforcement benefits.
4Shape
If vacuum pressure is applied to remove air from the stack, then conforming is improved, but air trapping occurs at bevels and protrusions
Solution Approach 1:
The invention changes the structural parameters of the ply stack by incorporating multiple fiber orientations that facilitate air evacuation. The specific stacking sequence with 0°, 90°, 45°, and 135° plies creates pathways and reduces resistance to air flow during vacuum application, allowing more effective air removal from difficult-to-reach areas like bevels and protrusions while maintaining good surface conformity.
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 approach effectively prevents wrinkles in composite articles, especially on tools with complex geometries, while also enabling the formation of thickened regions for reinforcement, resulting in a smoother outer surface and improved mechanical properties.
Implementation Method 1
it requires the use of pressure onto stacks of prepregs or plies against a tool. A vacuum bag is used to achieve a pressure such that wrinkles and trapped air in the stack can be forced out under vacuum pressure.
Implementation Method 2
A vacuum bag is used to achieve a pressure such that wrinkles and trapped air in the stack can be forced out under vacuum pressure.
Implementation Method 3
The vacuum bag can be used for curing the resin of the plies in an autoclave or in an oven at elevated temperature and pressure.
Data Source
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AI summary
The present invention relates to a method of forming an article on a tool, the tool having one longitudinal direction and one transversal direction, wherein the method comprises the steps of: -arranging a stack (22) of plies (23) comprising fibres, so that when positioned on the tool (21) the ply (24) arranged closest to the tool (21) and the ply (25) arranged furthest away from the tool (21) have the fibres substantially orthogonal (3) to the longitudinal direction (L) of the tool,and arranging at least one ply having the fibres substantially in the same direction (2) as the longitudinal direction (L) of the tool(21) between the plies having fibres substantially orthogonal (3) to the longitudinal direction of the tool (21), -conforming the stack to the tool with a forming medium; and -removing the article from the tool. The present invention also relates to an article produced according to the method.