Composite Stiffener Radius Gap Segmentation
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Solution Overview
Problem
Cracking in radius fillers of composite structures, particularly in aerospace applications, leads to delamination failures due to residual tensile strain and improper tooling, making it difficult to prevent crack formation entirely, especially as structures grow in size.
Innovation Solution
Incorporating an intermediate structure between stiffeners to split large radius gaps into smaller ones, reducing the likelihood of crack propagation by modifying the moment of inertia and restricting movement within the composite structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate structure is introduced between stiffeners to reduce radius gap size, then crack propagation is reduced and structural integrity is improved, but device complexity increases
Solution Approach 1:
The patent divides a large radius gap into multiple smaller radius gaps by introducing an intermediate structure (such as a intermediate stiffener or filler piece) between the main stiffener and the skin. This segmentation reduces the stress concentration in each individual gap, thereby preventing crack initiation and propagation while maintaining overall structural integrity.
Solution Approach 2:
The intermediate structure acts as a mediator element positioned between the main stiffener and the skin panel. This intermediary component distributes the thermal expansion stresses and mechanical loads more evenly, reducing the harmful stress concentration that would otherwise occur at a single large radius gap interface.
2Reliability
If residual tensile strain is reduced through improved tooling and handling, then crack formation is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The intermediate structure is designed to preemptively absorb and distribute thermal expansion stresses before they can concentrate at the radius gap interface. By providing this stress distribution mechanism in advance, the structure cushions against the harmful effects of residual tensile strains that occur during manufacturing and service, preventing crack formation without requiring perfectly controlled manufacturing conditions.
3Reliability
If the moment of inertia is modified to restrict movement in the composite structure, then crack propagation is reduced, but device complexity increases
Solution Approach 1:
By segmenting the radius gap into smaller gaps through the intermediate structure, the moment of inertia of the overall assembly is effectively modified. This segmentation creates multiple smaller stress paths rather than one large stress concentration point, restricting harmful movements and deformations that would lead to crack propagation.
Data Source
Figure 1~2
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AI summary
A composite structure (200) is provided. The composite structure (200) includes a first stiffener (208), a second stiffener (210), and an intermediate structure (216) positioned between the first and second stiffeners such that the first stiffener (208) is coupled to a first side (228) of the intermediate structure (216), and such that the second stiffener (210) is coupled to a second opposing side (230) of the intermediate structure (216). A first radius gap (218) is defined at least partially between the first stiffener (208) and the intermediate structure (216), and a second radius gap (220) is defined at least partially between the second stiffener and the intermediate structure.