Interleaved Composite Plank Stiffener for Panel Stress Reduction
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Solution Overview
Problem
Conventional composite plank stiffeners for panels, particularly in aircraft components, face issues with high free-edge intralaminar/interlaminar and thermal stresses due to their size and fiber layer configurations, leading to mechanical and thermal stress-related weaknesses.
Innovation Solution
The solution involves an interleaved layer construction of a composite panel with a plank stiffener composed of multiple sub-planks separated by adhesive layers, which are co-bonded to reduce stress transmission and alleviate residual stresses, and additional composite tapes interleaved within the panel to form a raised ridge for enhanced stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional composite plank stiffener is used, then the panel gains structural support, but high free-edge intralaminar/interlaminar and thermal stresses develop due to the plank's size and fiber layer configuration
Solution Approach 1:
The plank stiffener is divided into multiple discrete fiber layer groups stacked in the thickness direction, with each group containing multiple fiber layers. This segmentation allows independent stress management for each group while maintaining overall structural support, reducing the high free-edge intralaminar/interlaminar stresses that would develop in a conventional monolithic plank configuration
Solution Approach 2:
Different fiber layer groups are positioned at different locations within the plank thickness, with each group's fiber layers oriented to provide optimal local reinforcement. The fiber layers within each group are configured with specific orientations (including 0°, +45°, -45°, and 90° directions) to address local stress patterns, while the overall plank configuration provides global structural support, thereby reducing thermal and mechanical stresses through localized optimization
2Strength
If the plank thickness dimension is increased to provide greater stiffening, then mechanical stress and thermal stress in the plank increase
Solution Approach 1:
The thick plank is segmented into multiple discrete fiber layer groups stacked in the thickness direction. Each group contains multiple fiber layers that can be independently configured and cured. This segmentation reduces the continuous stress pathways that would exist in a monolithic thick plank, thereby reducing both mechanical stress and thermal stress while maintaining the overall stiffening capability through the combined effect of all groups
Solution Approach 2:
A matrix material is used as an intermediary substance between the discrete fiber layer groups. This matrix material allows for stress distribution and load transfer between groups while accommodating thermal expansion differences. The matrix material fills the spaces between fiber layers and groups, creating a composite structure that reduces stress concentrations while maintaining the thick plank's stiffening function
3Shape
If layers of composite material are stacked and co-cured to form a plank, then the plank configuration is achieved, but inherent weaknesses in the short transverse dimension are not addressed
Solution Approach 1:
Within each fiber layer group, fiber layers are oriented in multiple directions (0°, +45°, -45°, 90°) to provide localized reinforcement in the short transverse dimension and other critical directions. This multi-directional fiber arrangement addresses the inherent weaknesses of unidirectional composite layers by distributing loads across different orientations, strengthening the plank in directions perpendicular to the primary length direction while maintaining the overall plank configuration
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 construction effectively mitigates the stress-related weaknesses of conventional composite plank stiffeners, enhancing the mechanical and thermal stability of the panel while maintaining structural integrity.
Implementation Method 1
a first layer of adhesive on the bottom sub-plank; and, an intermediate sub-plank in the plank, the intermediate sub-plank engaging against the first layer of adhesive with the first layer of adhesive securing the intermediate sub-plank to the bottom sub-plank
Data Source
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AI summary
An interleaved layer construction of a composite panel (14) and a composite plank constructed of three sub-planks (16, 18, 22) that are adhered together and secured to the panel (14) stiffen and strengthen the panel (14).