Comparison of DOFS Attachment Methods for Time-Dependent Strain Sensing

Abstract

Structural health monitoring (SHM) is a challenge for many industries. Over the last decade, novel strain monitoring methods using optical fibers have been implemented for SHM in aerospace, energy storage, marine, and civil engineering structures. However, the practical attachment of optical fibers (OFs) to the component is still problematic. While monitoring, the amount of substrate strain lost by the OF attachment is often unclear, and difficult to predict under long-term loads. This investigation clarifies how different attachment methods perform under time-dependent loading. Optical fibers are attached on metal, thermoset composite, and thermoplastic substrates for distributed strain sensing. Strains along distributed optical fiber sensors (DOFS) are measured by optical backscatter reflectometry (OBR) and compared to contact extensometer strains under tensile creep loading. The quality of the bondline and its influence on the strain transfer is analyzed. Residual strains and strain fluctuations along the sensor fiber are correlated to the fiber attachment method. Results show that a machine-controlled attachment process (such as in situ 3-D printing) holds great promise for the future as it achieves a highly uniform bondline and provides accurate strain measurements.

Three-Dimensional-Printed Sensing Samples Embedding Fiber Bragg Gratings: Metrological Evaluation of Different Sample Materials and Fiber Coatings

“…The effect of different infills is analyzed in several studies [22], [27], [35], [36], [40], where the mechanical and thermal properties of the sensor are shown to vary according to infill density and geometry. Embedding the fiber during the 3D printing process is preferable to gluing it in a second moment or on the external surface, since the embedding process ensures a consistent bond between the surfaces and yields a better measurement accuracy [41], [42].…”