Stiffened CFRP Ribs for Thermal Mismatch
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Solution Overview
Problem
Aluminum side of body ribs used in aircraft with CFRP wing boxes face thermal expansion mismatches and high fatigue loads, leading to inefficiencies and increased costs due to added weight requirements.
Innovation Solution
The use of stiffened carbon fiber reinforced polymer (CFRP) side of body ribs with a combination of aluminum and thermoplastic or thermoset stiffeners, connected via fasteners or co-bonding/co-curing, to form a CFRP rib assembly that matches the thermal expansion of the CFRP wing box while providing structural reinforcement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If aluminum side of body ribs are used to match thermal expansion of aluminum wing boxes, then thermal expansion compatibility is improved, but thermal expansion mismatch occurs when used with CFRP wing boxes
Solution Approach 1:
The patent employs a composite structure combining CFRP rib webs with aluminum stiffeners. The CFRP portion matches the thermal expansion characteristics of the CFRP wing box, while the aluminum stiffeners provide the necessary structural reinforcement to withstand high fatigue loads. This composite approach allows the rib assembly to be compatible with both CFRP and aluminum wing box configurations.
2Strength
If aluminum side of body ribs are used to meet high fatigue load requirements, then structural strength is improved, but weight increases making it not cost effective
Solution Approach 1:
The patent applies local quality by using aluminum stiffeners only in specific locations where high fatigue load resistance is required, rather than making the entire rib assembly from aluminum. The CFRP rib webs provide sufficient strength for normal loading conditions, while the aluminum stiffeners are strategically placed to reinforce areas subject to high fatigue loads, thereby reducing overall weight while maintaining structural integrity.
Solution Approach 2:
The hybrid composite structure combines the lightweight properties of CFRP with the high strength-to-weight ratio of aluminum in critical areas. This allows the rib assembly to achieve the necessary fatigue load resistance without the penalty of using solid aluminum construction throughout, thus reducing overall weight and improving cost-effectiveness.
3Stability of the object's composition
If monolithic or built-up aluminum rib configurations are used, then structural integrity is maintained, but thermal expansion mismatch and weight issues arise with CFRP wing boxes
Solution Approach 1:
The patent segments the rib assembly into distinct CFRP rib web portions and aluminum stiffener portions. This segmentation allows each material to be optimized for its specific function: CFRP for thermal expansion compatibility and general structural support, and aluminum for localized fatigue load resistance. The segmented design maintains structural integrity through proper connection mechanisms while avoiding the weight and thermal expansion issues of monolithic aluminum construction.
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 solution effectively addresses thermal expansion mismatches and high fatigue loads, reducing weight and costs by utilizing CFRP materials that are more efficient and cost-effective than traditional aluminum ribs, while maintaining structural integrity.
Implementation Method 1
an exterior of the interference fit fasteners may include stripes of a coating separated by non-coated stripes
Data Source
AI summary
A side of body carbon fiber reinforced polymer (CFRP) composite rib assembly that is formed by connecting an aft CFRP rib web, a middle CFRP rib web, and a forward CFRP rib web together. The side of body CFRP rib assembly includes a plurality of stiffeners connected to the aft CFRP rib web, the middle CFRP rib web, or the forward CFRP rib web. A first stiffener connects the aft CFRP rib web with the middle CFRP rib web and a second stiffener connected the forward CFRP rib web to the middle CFRP rib web. The stiffeners may be connected via fasteners or may be co-bonded or co-cured with the side of body CFRP rib web. The stiffeners connected to the side of body CFRP rib assembly may include more than one shape and may be aluminum, a thermoset, and/or a thermoplastic.