Instrumented nut, clamping sleeve, clamping device and method for tightening such a nut

The instrumented nut with a piezoresistive conductive polymer and electrodes, along with electrical impedance tomography, addresses the inaccuracy of torque wrenches and adhesive strain gauges, providing precise preload control and enhanced reliability in screw tightening.

FR3162488A1Active Publication Date: 2025-11-28LISI AEROSPACE
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Patent Information

Application Number
FR2024005326
Authority / Receiving Office
FR · FR
Patent Type
Applications
Current Assignee / Owner
Filing Date
2024-05-24
Publication Date
2025-11-28
Estimated Expiration
2044-05-24

AI Technical Summary

Technical Problem

Existing methods for determining the preload in screws during tightening are inaccurate, as they rely on torque wrenches that do not account for friction coefficients, and strain gauges require durable adhesives that can fail over time.

Method used

An instrumented nut with a piezoresistive conductive polymer layer and electrodes, combined with a clamping device and electrical impedance tomography, allows precise preload adjustment with reduced additional cost and increased reliability.

Benefits of technology

The solution enables precise control of screw preload, ensuring long-term durability by accurately measuring deformation and stress without the limitations of torque wrenches and adhesive-based strain gauges.

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Abstract

Instrumented nut, clamping sleeve, clamping device and method for tightening such a nut. The invention relates to an instrumented metal nut (10b) comprising a tubular body having a polygonal drive surface (14). The nut comprises, on at least one annular portion (34) of its outer surface: an electrically insulating layer (36) applied to the annular portion; a piezoresistive conductive polymer (38) whose ohmic resistance varies according to a stress exerted during tightening of the nut on a threaded fastener, said conductive polymer being applied to the electrically insulating layer; and at least two electrodes (40). Figure for the abstract: Figure 2
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