Strain-Gauged Washer for Bolt Preload Measurement
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Solution Overview
Problem
Existing methods for measuring bolt preload in bolted joints are imprecise, costly, and require modifications to bolts or fastened components, making them unsuitable for applications where accuracy and simplicity are critical.
Innovation Solution
A strain-gauged washer with small, commercially available strain gauges embedded in slots within the washer, connected in series to enhance sensitivity, and made from materials that maximize strain while withstanding compressive loads, allowing direct measurement of compressive strain and bolt preload without altering the bolt or fastened components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thick collar is used in place of a standard washer to measure bolt preload, then measurement capability is improved, but the geometry of the bolted joint is changed, requiring different bolt length and dimensional changes to fastened components
Solution Approach 1:
The patent changes the parameter of washer thickness from conventional to a specific optimized thickness that allows strain gauge embedding while maintaining standard bolted joint geometry. This enables preload measurement without requiring different bolt lengths or dimensional changes to fastened components.
Solution Approach 2:
The patent embeds strain gauges within the thickness dimension of the washer, utilizing the internal volume rather than increasing external dimensions. This allows measurement capability to be added without changing the overall geometry of the bolted joint.
2Measurement precision
If strain gauges are placed in the washer to measure compressive strain, then measurement accuracy is improved, but the washer thickness must be increased to accommodate the gauges
Solution Approach 1:
The patent optimizes the washer thickness parameter to a specific value that provides sufficient space for strain gauge embedding while remaining within conventional thickness ranges. This allows accurate strain measurement without requiring excessively thick washers.
Solution Approach 2:
The patent embeds strain gauges within the washer thickness, nesting the measurement device inside the existing component rather than adding external dimensions. Multiple strain gauges are arranged in series within the available space to maximize measurement capability.
3Measurement precision
If multiple strain gauges are connected in series to increase effective gauge length, then measurement sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple strain gauges in series within the washer, merging their individual measurement capabilities into a single effective gauge with increased length and sensitivity. This approach achieves improved precision while keeping the overall device structure integrated and relatively simple.
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
Provides accurate, repeatable, and inexpensive bolt preload measurement, improving precision and reducing the need for modifications, enabling reliable measurement in various applications.
Implementation Method 1
one or more strain gauges placed in a slot in the washer and oriented through a thickness of the washer to measure compressive strain in the washer
Data Source
AI summary
This invention installs multiple miniature strain gauges inside a regular dimensioned bolt washer to accurately measure bolt preload. To enhance the strain gauge sensitivity, an alloy with low elastic modulus and high yield strength is selected to fabricate the metal washer. In addition, multiple gauges are connected in series to multiply the effective gauge length and enhance measurement sensitivity. Further, the stain gauges are encapsulated in the middle of the washer as opposed to on the external surface which offers much improved sensitivity and physical protection of the strain gauges.