Composite Stringer Ply Orientation for Stiffness and Weight
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Solution Overview
Problem
Existing composite stringers in aircraft face limitations in increasing specific strength and stiffness without adding weight, as high percentages of plies in a single primary load direction can weaken the stringer in non-primary load directions, leading to early cracks or splits, and traditional fiber orientations are inefficient in distributing loads.
Innovation Solution
The method involves orienting reinforcing fibers at ±α and ±β degrees with respect to the primary loading axis, where α is between 2 and 12 degrees, and β is between 50 and 85 degrees, to enhance strength in tension, compression, shear, and bearing loads, while reducing the number of plies needed for similar transverse strength, thereby increasing stiffness and reducing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high percentage of plies are oriented in a single primary load direction to increase stringer stiffness, then stringer stiffness in primary load direction is improved, but stringer strength in non-primary load direction deteriorates causing early cracks or splits
Solution Approach 1:
The patent applies local quality by varying fiber orientation angles in different plies of the composite stringer. Specifically, it uses a mix of 0-degree plies (for primary load stiffness) and ±45-degree plies (for non-primary load strength and crack suppression) in specific sequences. This local variation in fiber orientation within the composite structure allows simultaneous optimization of both primary and non-primary load performance without requiring uniform fiber distribution throughout the entire stringer.
2Strength
If more plies are added to increase stringer stiffness, then stringer stiffness is improved, but stringer weight increases
Solution Approach 1:
The patent applies parameter changes by optimizing the fiber orientation angles and ply sequence parameters of the composite stringer. Instead of simply adding more plies, it changes the orientation parameters (using specific combinations of 0-degree and ±45-degree plies) and sequence parameters to achieve higher stiffness-to-weight ratio. This allows the stringer to attain required stiffness levels with fewer plies, thereby reducing overall weight while maintaining structural performance.
3Ease of manufacture
If traditional fiber orientations (0/+45/-45/90 degrees) are used, then manufacturing standard compliance is improved, but load distribution efficiency deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the composite stringer into distinct ply groups with specific fiber orientations (0-degree plies and ±45-degree plies) arranged in a tailored sequence. This segmentation allows each ply group to perform its specialized function: 0-degree plies for primary load carrying and ±45-degree plies for shear and non-primary load resistance. The segmented ply architecture optimizes load distribution efficiency while maintaining compatibility with standard manufacturing processes through conventional autoclave curing and fiber placement techniques.
Data Source
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AI summary
An aerospace vehicle (100) includes a plurality of composite stiffeners (220). Each stiffener of the plurality has a stack of plies of reinforcing fibers. To increase stiffness without increased weight, at least some of the plies in the stack have reinforcing fibers oriented at ±α with respect to an axis of primary loading, where α is between 2 and 12 degrees. At least some of the plies in the stack have reinforcing fibers oriented at ±β with respect to the axis of primary loading, where β is between 50 and 85 degrees.