Fatigue Life Sensor with Crack Initiation Notch
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Solution Overview
Problem
Existing methods for measuring accumulated fatigue damage in structures subjected to repetitive loads, such as fatigue coupons and metal foil strain gauges, face challenges including structural weakening, limited sensitivity, and unintended crack propagation, which hinder accurate estimation of remaining fatigue life.
Innovation Solution
A sensor comprising a conductive foil with a crack initiation feature, bonded to a backing material, which increases electrical resistance as cracks propagate across the conductive path, allowing for more sensitive monitoring of fatigue progression without structural weakening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fatigue coupon is bolted onto the structure to measure fatigue damage, then the measurement capability is provided, but the structure is weakened and stress field is altered due to drilled holes
Solution Approach 1:
The patent extracts the measurement function from a separate bolted coupon and integrates it directly into the structure through surface-bonded strain gages. This eliminates the need for drilled holes and bolting, thereby maintaining structural strength while providing fatigue damage measurement capability through resistance change monitoring of the bonded gages
Solution Approach 2:
The patent uses an adhesive intermediary to bond the strain gage to the structure surface. This adhesive layer transfers strain from the structure to the gage without requiring mechanical fasteners, thus avoiding holes that would weaken the structure while enabling accurate strain and fatigue damage measurement
2Strength
If a metal foil strain gage is used to measure fatigue damage, then the measurement is provided without structural weakening, but the sensitivity is limited and unintended cracks may propagate
Solution Approach 1:
The patent applies local quality by placing crack initiation features (notches, holes, or surface defects) at specific locations on the structure where fatigue damage is most likely to occur. This concentrates the measurement function in high-stress regions, enhancing sensitivity to fatigue damage while maintaining overall structural integrity through localized rather than widespread modifications
Solution Approach 2:
The patent changes the physical state of the foil from annealed/softened to a condition where work hardening occurs during cyclic loading. This parameter change causes the foil to develop measurable resistance increases and controlled crack propagation that enhances sensitivity to fatigue damage while the adhesive bonding prevents unintended crack propagation in the structure
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 sensor provides a more perceptible and accurate measurement of fatigue damage, enabling effective tracking of structural fatigue life and timely removal from service, while minimizing unintended crack formation and maintaining structural integrity.
Implementation Method 1
A sensor includes a conductive path along which electrical current flows at an initial resistance measured prior to the structure being subjected to repetitive loads. One or more cracks propagate from the crack initiation feature across the conductive path to cause electrical resistance to increase
Implementation Method 2
A sensor comprises a conductive foil with a crack initiation feature, bonded to a backing material
Data Source
AI summary
A sensor for measuring the fatigue life of a structure subjected to repetitive loads is disclosed. The sensor includes a backing material arranged for securement to the structure, and a foil arranged for securement to the backing material. The foil includes a conductive path along which electrical current flows at an initial resistance measured prior to the structure being subjected to repetitive loads. A crack initiation feature in the form of a notch is located on the conductive path. In response to repetitive loads applied to the structure, one or more cracks propagate from the crack initiation feature across the conductive path to cause electrical resistance to increase whereby the progression of fatiguing of the structure may be determined.