Chopped Fiber Gap Filler for Aircraft Stringer Cracking
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Solution Overview
Problem
Aircraft stringer gaps filled with laminate structures or uni-noodles are prone to cracking due to thermal and mechanical property differences, leading to weakened stiffener interfaces and reduced load-carrying capabilities, necessitating additional reinforcement.
Innovation Solution
The use of a gap filler made from chopped carbon fibers oriented in multiple directions, mixed with a thermoset resin, which are randomly distributed throughout the filler to match the thermal expansion rates of the stringer and skin, reducing stress and preventing cracking, and are inserted into the stringer gaps and covered with a skin for curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If laminate structures or uni-noodles are used to fill stringer gaps, then the gaps are filled and structural continuity is provided, but cracking occurs due to thermal and mechanical property differences
Solution Approach 1:
The patent changes the material parameters of the gap filler by using chopped carbon fibers with a coefficient of thermal expansion matched to the stringer and skin materials. This parameter matching prevents thermal stress accumulation that causes cracking, while the chopped fiber configuration provides structural continuity to fill the gap effectively.
Solution Approach 2:
The patent employs a composite material consisting of chopped carbon fibers embedded in a matrix material. This composite structure combines the high strength and thermal expansion characteristics of carbon fibers with the binding properties of the matrix, creating a gap filler that simultaneously provides structural continuity and cracking resistance through multi-directional fiber reinforcement.
2Strength
If gap filler is inserted into stringer gaps and covered with skin, then the stringer assembly strength is enhanced, but additional reinforcement may be needed with conventional fillers
Solution Approach 1:
By changing the material parameters of the gap filler to match the thermal and mechanical properties of the surrounding stringer and skin components, the patent eliminates the need for additional reinforcement. The matched coefficient of thermal expansion prevents differential stress that would otherwise require extra reinforcement elements.
Solution Approach 2:
The patent achieves homogeneity in material properties between the gap filler and the surrounding structure. The chopped carbon fiber composite is formulated to have similar thermal expansion and mechanical characteristics to the stringer and skin, creating a homogeneous assembly that behaves uniformly under thermal and mechanical loads without requiring additional reinforcement.
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
The multi-directional chopped fiber gap filler relieves thermal stress, enhances the structural integrity of the stringer interface, and reduces the likelihood of cracking, thereby increasing the strength and reliability of the stringer assembly while minimizing additional reinforcement needs.
Implementation Method 1
chopped carbon fibers oriented in multiple directions, mixed with a thermoset resin, which are randomly distributed throughout the filler to match the thermal expansion rates of the stringer and skin, reducing stress and preventing cracking
Data Source
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AI summary
A method to increase strength and toughness of aircraft structural components is disclosed. An examplary component includes a composite structure (208) of an aircraft, a stringer (200) coupled to the composite structure (208) of the aircraft, where the stringer (200) and the composite structure (208) form a stringer radius gap. A gap filler (202) is disposed in the stringer radius gap, which includes chopped fibers randomly distributed throughout an entire volume of the gap filler (202).