Contoured Composite Stiffener Fabrication via Variable Mandrel Geometry
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Solution Overview
Problem
The existing methods for fabricating composite structures, such as stiffeners, often result in wrinkling due to deformation and high friction during the lay-up process, especially when forming over contoured surfaces, leading to undesirable properties, material waste, and increased thickness and weight.
Innovation Solution
A method and apparatus that tailor the geometry of a lay-up mandrel to accommodate the material characteristics of the stiffener, allowing continuous fiber reinforcement without wrinkling by selectively widening or narrowing the mandrel to match the stiffener's curvature, thereby eliminating the need for cutting and splicing plies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If pre-preg plies are cut into sections and spliced together to form contoured stiffeners, then the contour curvature can be achieved, but the structural properties are reduced and additional plies are required increasing thickness and weight
Solution Approach 1:
The mandrel is designed with variable cross-sectional geometry that dynamically adapts to the desired stiffener contour. By selectively widening or narrowing the mandrel cross-section along its length, the apparatus enables continuous fiber reinforcement to conform to complex curvatures without cutting or splicing, thereby maintaining structural integrity while achieving the required shape
Solution Approach 2:
The mandrel geometry parameters (cross-sectional width, height, and contour profile) are specifically tailored to match the desired stiffener geometry. By changing the mandrel parameters along its length, the system enables continuous plies to be formed into contoured shapes without compromising fiber continuity or requiring additional corrective plies
2Shape
If pre-preg plies are cut and spliced to achieve desired curvature, then the contour can be formed, but the manufacturing process becomes time consuming and labor intensive
Solution Approach 1:
The variable cross-sectional mandrel provides a continuous, pre-configured form that guides the lay-up of continuous plies directly into the final contoured shape. This eliminates the need for sequential cutting, splicing, and positioning operations, significantly reducing manufacturing time and labor requirements while maintaining the desired curvature
Solution Approach 2:
The mandrel is pre-formed with the exact variable geometry required for the final stiffener contour. This preliminary preparation of the forming surface allows continuous plies to be draped and consolidated directly into the final shape in a single operation, eliminating subsequent machining or assembly steps
3Shape
If pre-preg plies are cut and spliced to form contoured stiffeners, then the curvature can be achieved, but material waste increases
Solution Approach 1:
The variable cross-sectional mandrel is designed to exactly match the desired stiffener geometry, allowing continuous plies to be formed to the precise final dimensions. This eliminates the need for over-material application and subsequent trimming, as well as the waste associated with cutting and splicing operations, thereby minimizing material loss
4Strength
If additional plies or doublers are added to compensate for cutting and splicing, then structural properties can be maintained, but the thickness and weight of the stiffener increase
Solution Approach 1:
The variable cross-sectional mandrel enables continuous fiber reinforcement to be formed directly into the final contoured stiffener geometry without cutting or splicing. This maintains full structural properties with the minimum required ply count, eliminating the need for additional weight-bearing doublers or plies that would be required to compensate for discontinuities created by cutting and splicing
Data Source
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AI summary
A mandrel having an out-of-plane curvature and a corresponding in-plane change in mandrel geometry is used to fabricate substantially wrinkle-free, fiber reinforced stiffeners having an out-of-plane curvature.