CFRP Stringer Termination Softening via Web Trim and Noodle
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Solution Overview
Problem
Conventional stringer runouts in aircraft and vehicles experience delamination and disbonding due to load discontinuity, leading to increased part numbers and costs, as existing solutions require specific designs for each load condition.
Innovation Solution
A stringer design with a longitudinal length defining an acreage, transition, and runout region, featuring a base flange, web, and noodle, where the noodle has a unidirectional fiber top portion and a stacked laminate bottom portion with varying ply orientations, and the web is trimmed to reduce cross-sectional area and modulus of elasticity, thereby softening the stringer termination end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional web trim curvatures and radius fillers are used to address load discontinuity at stringer runouts, then delamination damage growth is mitigated, but the number of parts increases and manufacturing complexity increases
Solution Approach 1:
The patent combines the web trim curvature and radius filler functions into a single integrated stringer runout design. The stringer web is trimmed with a specific curvature that simultaneously addresses load discontinuity and eliminates the need for separate radius filler components, thereby reducing part numbers while maintaining delamination mitigation
Solution Approach 2:
The patent creates a universal stringer runout design that can be applied across multiple aircraft types and load conditions. The standardized web trim curvature and runout geometry provide delamination mitigation for various applications, reducing the need for custom-designed stringers for each specific implementation
2Reliability
If custom stringer designs are created for specific load conditions, then delamination is controlled for that application, but part numbers increase and costs increase
Solution Approach 1:
The patent develops a universal stringer runout design with standardized web trim curvature and geometry that can be applied across multiple aircraft types and loading scenarios. This single design provides delamination control for various applications without requiring custom designs, thereby reducing part numbers and associated costs while maintaining effectiveness
3Force
If stringer cross-sectional area is reduced at runout, then load discontinuity is decreased, but stringer strength is reduced
Solution Approach 1:
The patent applies local quality by trimming the web curvature specifically at the runout region while maintaining the full cross-sectional area and strength properties in the main body of the stringer. The localized web trim at the termination end reduces load discontinuity without compromising the overall stringer strength, as the reduced section is confined to the runout area where full strength is less critical
Data Source
Figure 1A~1B
Figure 2A~2D
Figure 3A~3B
AI summary
A stringer (100) and corresponding method is provided having a runout design that softens the stringer. According to one aspect, the stringer includes a base flange (104), a web (102), and a noodle (114). The noodle (114) includes a unidirectional fiber top portion (212) and a stacked laminate bottom portion (210, 220) coupled to the top portion (212). The bottom portion (210, 220) includes a number of stacks (229A, 220B), each stack including three plies (108A, 108B, 108C) having three corresponding fiber orientations within an acreage region (202) of the stringer (100). In a transition region (204) of the stringer, the stacked laminate bottom portion (210, 220) includes a number of stacks (220B), each stack including the first and third plies (108A, 108C) of the acreage region. According to another aspect, the base flange is softened by dropping plies within the transition region. Yet another aspect includes trimming the web down to the noodle, while trimming through the noodle according to a trim radius to a height proximate the base flange.