Comparison of DOFS Attachment Methods for Time-Dependent Strain Sensing

Area of Science:

• Materials Science
• Mechanical Engineering
• Sensor Technology

Background:

• Structural health monitoring (SHM) increasingly utilizes optical fibers (OFs) for strain sensing in critical sectors like aerospace and civil engineering.
• A significant challenge in OF-based SHM is the reliable attachment of sensors to diverse substrates, impacting strain transfer accuracy.
• Predicting strain loss due to attachment methods under long-term, time-dependent loading remains difficult.

Purpose of the Study:

• To investigate and compare the performance of different optical fiber attachment methods on various substrates under time-dependent loading.
• To analyze the influence of bondline quality on strain transfer efficiency and accuracy.
• To correlate residual strains and fluctuations with specific fiber attachment techniques.

Main Methods:

• Optical fibers were attached to metal, thermoset composite, and thermoplastic substrates.
• Distributed strain sensing was performed using optical backscatter reflectometry (OBR).
• Strains measured by distributed optical fiber sensors (DOFS) were compared against contact extensometer measurements during tensile creep tests.

Main Results:

• The quality of the bondline significantly affects strain transfer from the substrate to the optical fiber.
• Machine-controlled attachment processes, exemplified by in situ 3-D printing, yielded highly uniform bondlines.
• These uniform bondlines resulted in more accurate strain measurements compared to other methods.

Conclusions:

• Optimizing the attachment method is crucial for maximizing strain transfer accuracy in optical fiber-based SHM.
• In situ 3-D printing demonstrates a promising approach for achieving consistent and reliable optical fiber sensor attachment.
• Further development of automated attachment processes can enhance the long-term performance and predictive capability of SHM systems.