Load-Indicating Washer with Collapsible Domed Cap
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Solution Overview
Problem
Current load-indicating washers for fasteners lack an effective mechanism to accurately measure and indicate preload thresholds in structural joints, particularly in aerospace manufacturing, where precise load distribution is critical to prevent over-stressing and ensure structural integrity.
Innovation Solution
A load-indicating washer with a domed cap that collapses into a cavity when the clamping force exceeds its yield strength, providing a mechanical indication of the load threshold through plastic deformation, allowing for the determination of clamp-up load at joints and preventing additional preload that could compromise structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional washers are used to distribute load, then load distribution is achieved, but preload indication capability is lost
Solution Approach 1:
The patent combines the load distribution function of a traditional washer with the preload indication function into a single integrated component. The domed cap structure serves both to distribute the fastener load across the joint surface and to indicate preload status through its deformation state, eliminating the need for separate indication devices.
Solution Approach 2:
The washer performs self-indication of preload status through the deformation of its own domed cap structure. The component uses its inherent structural properties to provide measurement information without requiring external sensors or additional systems, making the indication function intrinsic to the washer itself.
2Reliability
If domed cap is designed to collapse at yield strength, then preload threshold indication is achieved, but structural integrity risk increases
Solution Approach 1:
The washer is segmented into distinct functional zones: the domed cap portion designed for controlled deformation at specific load thresholds, and the flatter base portion that maintains structural integrity and load distribution. This segmentation allows different parts to serve different functions - indication versus structural support.
Solution Approach 2:
The domed cap is designed with specific geometric parameters (dome height, base radius, wall thickness) that determine its yield strength and collapse load. By carefully selecting these parameters, the washer collapses at a predetermined safe threshold well below the failure load of the joint, providing a safety margin while maintaining overall structural integrity.
3Strength
If washer material is made metallic for strength, then structural durability is improved, but manufacturing precision control becomes more difficult
Solution Approach 1:
The design uses metallic material with controlled physical properties and carefully selected geometric parameters of the domed cap to achieve predictable deformation behavior. The yield strength of the metal combined with the specific dome geometry creates a reliable collapse threshold that can be manufactured within standard tolerances.
Solution Approach 2:
The domed cap is designed as a disposable indication element that is replaced after use. This allows the use of metallic materials with inherent variability while maintaining precision through replacement rather than through extremely tight manufacturing tolerances on each individual component.
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 washer effectively indicates when the clamp-up load exceeds acceptable thresholds, preventing over-stressing and ensuring the structural integrity of joints by providing a clear mechanical response, which can be used to verify manufacturing tolerances and prevent structural damage.
Implementation Method 1
the domed cap is configured to collapse into the cavity upon application of a clamping force by the fastener that exceeds a yield strength of the domed cap
Data Source
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AI summary
A load-indicating washer for use with a fastener. The washer is comprised of a circular base plate, a domed cap that projects from the base plate, a cavity formed between the circular base plate and the domed cap, and a fastener hole that extends through the circular base plate and the domed cap. The domed cap is configured to collapse into the cavity upon application of a force that exceeds a threshold.