Permeable Radius Filler for Composite Structures
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Solution Overview
Problem
Conventional methods for manufacturing radius fillers in composite structures are labor-intensive, time-consuming, and result in mismatched axial stiffness between the radius filler and the composite base member, leading to undesirable strength characteristics, particularly at the terminal ends of composite stringers.
Innovation Solution
A method involving the use of a permeable radius filler element that absorbs resin from the composite base member, which is then cured to bond the filler to the base member, reducing axial stiffness mismatch and improving strength characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If individual strips of prepreg composite material are laid up ply-by-ply into the radius cavity, then the radius filler can be manufactured to match the cavity shape, but the process becomes labor-intensive and time-consuming
Solution Approach 1:
The radius filler is divided into multiple pre-cut strips that can be independently prepared and then quickly assembled into the radius cavity. This segmentation allows each strip to be optimized for specific sections of the cavity while enabling parallel preparation and faster installation compared to sequential ply-by-ply construction.
Solution Approach 2:
The composite strips are pre-cut to precise widths and pre-formed to match specific portions of the radius cavity shape before installation. This preliminary preparation of strips with correct dimensions and curvatures eliminates time-consuming on-site shaping and assembly operations, significantly improving manufacturing productivity while maintaining precision.
2Strength
If unidirectional reinforcing fibers are used in the radius filler, then the axial stiffness of the radius filler increases, but this creates a mismatch with the axial stiffness of the composite base member leading to undesirable strength characteristics
Solution Approach 1:
Different sections of the radius filler are constructed with different fiber orientations and material properties to match the local stiffness requirements of the composite base member. The terminal ends use materials with reduced axial stiffness to match the lower stiffness of the base member at those locations, while central sections may use higher stiffness materials where needed. This localized variation in material properties eliminates the stiffness mismatch problem.
Solution Approach 2:
The axial stiffness parameter of the radius filler is varied along its length by changing fiber orientation angles, material composition, or ply stacking sequences. This allows the radius filler's axial stiffness to be dynamically adjusted to match the varying stiffness profile of the composite base member, preventing stress concentrations and improving overall structural reliability.
3Reliability
If a laminating machine is used to manufacture the radius filler with non-zero degree fiber orientations, then the axial stiffness mismatch is reduced, but the capital expense for construction, operation, and maintenance increases significantly
Solution Approach 1:
Instead of using expensive automated laminating machines, the solution uses manually laid-up composite strips that are pre-formed to match the desired fiber orientation patterns. The strip designs replicate the stiffness-matching profiles that would otherwise require complex automated equipment, achieving the same reliability benefit through simpler, more cost-effective means.
Solution Approach 2:
The solution employs disposable or reusable manual layup tools and pre-formed composite strips rather than investing in expensive, complex automated laminating machinery. This approach achieves the necessary fiber orientation control through straightforward manual processes, significantly reducing capital expenses while maintaining the ability to create stiffness-matched radius fillers.
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
The method enhances the strength and durability of composite structures by reducing axial stiffness mismatch and preventing cracking, while also being more efficient and cost-effective than traditional methods.
Implementation Method 1
absorbing resin from the composite base member into the permeable material of the radius filler element
Data Source
AI summary
A method of manufacturing a cured composite structure includes placing a radius filler element into a radius cavity extending along a length of a composite base member. The radius filler element is formed of a permeable material. The method also includes absorbing resin from the composite base member into the permeable material of the radius filler element. The method additionally includes curing or solidifying the resin in the radius filler element and in the composite base member to form a cured composite structure in which the resin bonds the radius filler element to the composite base member.