Washer Enlarged Bore for Composite Joint Strength
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Solution Overview
Problem
Conventional composite joints face challenges in strength reduction due to bolt installation, weight increase, and rework complexity, particularly in aircraft structures, where conventional straps add manufacturing costs and weight while increasing rework time.
Innovation Solution
A fastening system comprising a fastener, a washer with an enlarged chamfered or countersunk bore, and a collar, which distributes force away from the hole edge, enhancing the filled-hole tensile strength and reducing the weight of the composite joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional straps are used in composite joints, then clamp-up stress distribution is reduced, but device complexity and weight increase
Solution Approach 1:
The patent removes the strap component from the joint assembly and extracts its stress-distribution function into the washer design. The washer with enlarged bore and chamfer directly provides the stress distribution function that previously required a separate strap component, thereby reducing device complexity while maintaining strength.
Solution Approach 2:
The patent merges the stress distribution function (previously performed by the strap) into the washer component. By combining these functions into a single integrated washer design with enlarged bore and chamfer, the joint structure becomes simpler while achieving the same clamp-up stress distribution effect.
2Strength
If conventional straps are used in composite joints, then clamp-up stress distribution is reduced, but weight increases
Solution Approach 1:
The patent extracts the weight burden from the joint structure by eliminating the strap component. The washer with enlarged bore and chamfer provides the necessary stress distribution function without adding the extra weight of a separate strap, achieving weight reduction while maintaining strength.
3Ease of manufacture
If bolts are installed in composite panels, then composite panels are joined, but tensile strength near hole edges decreases
Solution Approach 1:
The patent applies beforehand cushioning by providing the washer with enlarged bore and chamfer before the bolt is installed. This pre-positioned washer structure cushions and distributes the clamp-up load away from the hole edges before stress concentration can occur, protecting the composite material from damage and maintaining tensile strength.
Solution Approach 2:
The washer acts as an intermediary component between the bolt and the composite panel. It mediates the stress transfer by distributing the clamp-up load over a larger area and directing it away from the critical hole edges, thereby protecting the panel while enabling the joining function.
4Strength
If washers are used to distribute force, then tensile strength increases, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the washer geometry - specifically enlarging the bore and adding a chamfer. These geometric parameter changes enable the washer to distribute force more effectively and increase tensile strength, while the modifications remain within standard manufacturing capabilities for simple disc-shaped components.
Data Source
AI summary
A fastening system comprises a fastener, a washer, and a collar. The fastener has a shaft extending through a hole in a composite panel. The washer is concentrically positioned on the shaft between a head of the fastener and the composite panel. The washer comprises an enlarged bore facing the composite panel. The enlarged bore is one of a chamfered bore or a countersunk bore. The collar secures the fastener relative to the composite panel.