Embedded Sensor Fasteners for Crack Detection
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Solution Overview
Problem
In aircraft components with multiple layers joined by fasteners, inconsistencies in clamp-up and preloading, along with damage such as galling, can mask crack detection, leading to reduced aircraft life and high inspection and rework costs, as conventional nondestructive testing methods struggle to accurately assess material conditions near fasteners.
Innovation Solution
Embedding sensor conductors into fasteners to create an interrogating field and measure responses, allowing for nondestructive evaluation of material conditions, including stress, cracks, and temperature, while using state-sensitive indicator layers to enhance sensitivity, and integrating sensors into the fastener structure for easier installation and deeper penetration of inspection fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional eddy-current sensors are used to inspect damage around fasteners, then nondestructive evaluation can be performed, but the fastener and material edges strongly influence the sensor response and mask crack detection
Solution Approach 1:
The patent extracts the sensor functionality from external conventional eddy-current sensors and embeds it directly into the fastener structure. The fastener itself becomes the sensing element, with sensor conductors integrated into the fastener body, allowing the fastener to sense material conditions without being interfered with by external sensor placement issues
Solution Approach 2:
The patent merges the fastener's mechanical joining function with the sensor's detection function into a single integrated component. The fastener structure incorporates sensor conductors that generate interrogating fields and detect material conditions, combining structural and sensing roles in one element
2Measurement precision
If bolt-hole eddy current testing is performed to inspect material near fasteners, then damage can be evaluated, but the fastener must be removed by drilling out
Solution Approach 1:
The fastener performs self-diagnosis by incorporating sensor conductors that continuously monitor material conditions around the fastener hole. The fastener itself generates the interrogating field and detects changes in material properties, eliminating the need for external inspection equipment and fastener removal
Solution Approach 2:
The sensor conductors are embedded into the fastener structure during manufacturing, preparing the fastener for future monitoring functions before actual use. This preliminary integration of sensing capability allows immediate inspection upon installation without requiring subsequent removal or disassembly
3Measurement precision
If sensor conductors are embedded into fasteners for continuous monitoring, then crack detection accuracy improves, but fastener structure complexity increases
Solution Approach 1:
The fastener is designed to perform multiple functions simultaneously: mechanical joining, generating interrogating electromagnetic fields, and sensing material conditions. The sensor conductors are integrated into the fastener structure, allowing the same component to serve both structural and sensing roles without requiring separate dedicated sensing elements
Solution Approach 2:
The patent changes the electrical parameters of the fastener by incorporating conductive elements that can generate and detect electromagnetic fields. The fastener's material properties or attached indicator layers are modified to be sensitive to stress, temperature, or damage states, enabling sensing capability through parameter changes rather than adding complex mechanical sensing mechanisms
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
This approach enables effective monitoring of material conditions and damage around fasteners without removing them, improving detection accuracy and reducing inspection costs by allowing for cradle-to-grave monitoring and enhanced functional performance.
Implementation Method 1
a fastener that has an integrated or embedded drive conductor which is used to impose a magnetic field in the test material
Implementation Method 2
conventional eddy-current sensing involves the excitation of a conducting winding, the primary, with an electric current source of prescribed frequency. This produces a time-varying magnetic field
Implementation Method 3
measuring a response of a sense conductor near the test material
Data Source
AI summary
Damage and usage conditions in the vicinity of fasteners in joined structures are nondestructively evaluated using the fasteners themselves. Sensors or sensor conductors are embedded in the fasteners or integrated within the fastener construct, either in the clearance gap between the fastener and the structure material or as an insert inside the shaft or pin of the fastener. The response of the material to an interrogating magnetic or electric field is then measured with drive and sense electrodes both incorporated into the fastener or with either drive or sense electrodes external to the fastener on the material surface. In another configuration, an electric current is applied to one or more fasteners and the electric potential is measured at locations typically between the driven electrodes applying the current. The potential is measured circumferentially around the fastener at locations on the material surface or across pairs of fasteners throughout or along the joint. The voltage or potential measurement electrodes may be collinear with the drive electrodes. State sensitive material layers can be added either to the fastener or the test material layers in order to enhance observability of the test material condition, such as the presence of a crack, mechanical stress, delamination, or disbond.