Fabric Jacketed Unidirectional Noodle for Aircraft Spar Crack Resistance
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Solution Overview
Problem
Composite radius filler noodles in aircraft spars are prone to cracking due to thermal and mechanical stresses, which weakens the spar structure.
Innovation Solution
A composite radius filler noodle with a triangular core made of unidirectional pre-preg tape and covered with multiple layers of pre-preg fabric strips, which are pultruded or die-formed to create a fabric jacket that prevents crack propagation by providing higher fracture toughness and an arduous crack path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a composite radius filler noodle is used to fill gaps in aircraft spars, then the structural integrity of the spar is improved, but the noodle is prone to cracking due to thermal and mechanical stresses during curing and service
Solution Approach 1:
The noodle is segmented into a core region and a jacket region with distinct material compositions. The core uses unidirectional pre-preg tape for strength, while the jacket uses woven fabric for crack resistance. This segmentation allows each region to perform its specialized function without compromising the other.
Solution Approach 2:
The noodle employs a composite structure combining two different pre-preg materials: unidirectional pre-preg tape in the core and woven fabric pre-preg in the jacket. This composite approach leverages the high strength of unidirectional fibers and the crack-resistant properties of woven fabrics to achieve both structural integrity and reliability.
2Reliability
If multiple layers of fabric strips are added to the noodle to prevent crack propagation, then the fracture toughness is improved, but the manufacturing complexity increases
Solution Approach 1:
The woven fabric pre-preg jacket acts as a flexible protective shell around the core. This thin film structure provides crack resistance and fracture toughness while maintaining a relatively simple overall geometry that can be manufactured using conventional composite layup techniques.
3Reliability
If the noodle core is reduced in size to reduce thermal cracking, then the crack initiation risk is reduced, but the structural strength may be compromised
Solution Approach 1:
Different regions of the noodle are assigned different material qualities based on their functional requirements. The core uses unidirectional pre-preg tape optimized for strength, while the jacket uses woven fabric optimized for crack resistance. This local differentiation allows the core to remain relatively small without compromising overall structural strength.
Data Source
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AI summary
A composite, radius filler noodle comprising: a core (54) having a triangular cross-section configuration and first (56), second (58) and third (60) surfaces that extend along a length of the core; a plurality of pre-preg fabric first (64) strips stacked on the core first surface, the plurality of first strips having lengths that extend completely along the core length; a plurality of pre-preg fabric second (66) strips stacked on the core second surface, the plurality of second strips having lengths that extend completely along the core length; and, a plurality of pre-preg fabric third (68) strips stacked on the core third surface, the plurality of third strips having lengths that extend completely along the core length. Also claimed is a method for constructing a composite radius filler noodle.