Integrated Composite Strut Ends for Fatigue-Resistant Load Transfer
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Solution Overview
Problem
Current strut designs using metal end fittings in composite solutions suffer from weak joints, stiffness mismatch, and thermal expansion issues, leading to fatigue failure and suboptimal use of composite strength.
Innovation Solution
A continuous reinforced composite strut with integrated composite ends, utilizing robotic fiber placement of continuous fiber thermoplastic composites to create a structure with minimal metal, allowing continuous fibers to traverse the entire length and withstand loads efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal end fittings are used in composite strut solutions, then reliability and proven lifespan are improved, but weight increases and fatigue failure risk increases due to stiffness mismatch and CTE mismatch at the metal-composite joint
Solution Approach 1:
The patent merges the metal end fitting and composite strut body into a single integrated composite structure. The strut comprises a composite tube with integrated end fittings made from the same composite material, eliminating the metal-composite joint entirely. This integration removes the stiffness mismatch and CTE mismatch problems that cause fatigue failure, while simultaneously reducing weight by eliminating heavy metal components.
Solution Approach 2:
The patent uses composite materials for both the tube and end fittings, replacing traditional metal end fittings with composite end fittings that have matched mechanical properties to the tube. This allows the entire strut to be made from composite materials with consistent stiffness and thermal expansion characteristics, eliminating the weak joint between dissimilar materials while maintaining reliability.
2Strength
If metal end fittings are used in composite strut solutions, then structural strength at joints is improved, but fatigue failure increases due to stiffness mismatch and CTE mismatch at the metal-composite joint
Solution Approach 1:
The patent combines the tube and end fittings into a single monolithic composite structure, eliminating the metal-composite joint that creates stress concentrations and fatigue failure points. The integrated design ensures continuous fiber reinforcement throughout the entire strut, including the end fittings, providing both strength and fatigue resistance without the mismatch problems of dissimilar materials.
3Ease of manufacture
If continuous fibers are cut at joints to connect metal ends, then ease of manufacture is improved, but composite strength is reduced because the continuous composite fiber is cut at a joint
Solution Approach 1:
The patent merges the manufacturing process into a single integrated operation where continuous fibers are laid through the entire strut length including the end fittings without cutting. The composite end fittings are manufactured in-place as part of the tube, allowing continuous fiber reinforcement to extend through what would traditionally be a joint location, maintaining both strength and manufacturing efficiency.
4Ease of manufacture
If conventional filament winding operation is used, then ease of manufacture is improved, but strength is reduced due to alignment of the fibers not being optimized
Solution Approach 1:
The patent applies local quality by optimizing fiber alignment specifically at the end fittings and joint regions where loads are transferred. The manufacturing process places continuous fibers in precise orientations matched to the local stress patterns, with fibers running longitudinally through the tube and integrated into the end fittings. This localized fiber optimization maximizes strength at critical locations while maintaining manufacturing efficiency.
Data Source
AI summary
A composite strut includes a first end and first aperture opposite a second end and second aperture separated by a strut distance along a longitudinal axis. A compression block is disposed between the first and the second aperture. A tension strap has a first continuous fiber reinforced plastic composite wrapped repeatedly around the first aperture, along the top side of the compression block, around the second aperture and along the bottom side of the compression block at least two times, wherein fibers of the tension strap are oriented extending parallel to the longitudinal axis between the first and second apertures. An overwind has a second continuous fiber reinforced plastic composite wrapped repeatedly around the first continuous fiber reinforced plastic composite and the compression block between the first end and second end at least two times, wherein fibers of the overwind are oriented extending around the longitudinal axis.