Strain monitoring of a single-lap joint with embedded fiber-optic distributed sensors

Abstract

We have developed a fiber-optic distributed sensor which can measure strain distributions along fiber Bragg grating (FBG) with the high spatial resolution. This sensing system is based on optical frequency domain reflectometry and a long-length FBG whose length is about 100 mm can be used. We can identify the longitudinal strain at an arbitrary position along the FBG using signal processing technology. In this study, long-length FBGs were embedded into the adhesive layers of the two single-lap joints and we could successfully measure the strain distributions inside the adhesives. In one single-lap joint, the adherends were carbon fiber reinforced plastics and in another one, they were aluminum. The adhesive was epoxy in both cases. The measured results were compared with the calculated ones by nonlinear finite element (FE) analysis in which the large displacement and the elasto-plastic response of the adherend or adhesive material were account for. We found that in most of the applied loads, the agreement between the measured results and the calculated ones obtained from an intact FE model is excellent. While the measured strain distributions inside the adhesive layer of the aluminum single-lap joint were varied at the end of the overlap in the higher applied loads and they were much different from those of the intact model, an FE model with debonding was made and it could represent such variations. We could also monitor the strain distributions inside the adhesive during the manufacturing process and we observed the perturbation in residual strain distributions after curing. Consequently, we can say that the fiber-optic distributed sensor with the high spatial resolution is very useful not only to assess the structural integrity of adhesive joints but also to improve numerical analysis techniques and manufacturing processes for them.

Tensile force of geogrids embedded in pile-supported reinforced embankment: A full-scale experimental study

“…They have many unique advantages over the traditional electrical sensors such as light weight, small size, immunity to electromagnetic interference, and long-distance and wide-range measurement capability (Nichols et al, 2007;Yan et al, 2011;Yoon et al, 2011;Murayama et al, 2012). Several researchers have employed FBG sensors to measure the geosynthetic strain in reinforced embankments or landfills (Brianҫ;on and Simon, 2012; Zamara et al, 2012).…”

Evaluation of mode II fatigue disbonding using Central Cut Plies specimen and distributed strain sensing technology

“…[40][41][42][43][44] Among several possibilities, an interesting approach uses back-face strain measurements and correlates them to the damage evolution. [45,46] This method presented some improvements with the use of fiber optics and distributed strain sensing technology [47][48][49][50][51] and it seems to give valuable information about damage evolution on bonded joints. For this work, the compliance method using a clip extensometer was used to calculate the disbond growth rate of CCP specimens along with a backface strain measurement technique using optical fibers.…”

Structural health monitoring by using fiber-optic distributed strain sensors with high spatial resolution

“…In this paper, we show an application of the distributed sensing system to strain monitoring and damage detection of an adhesive joint [16].…”

“…So the authors have developed the sensing system to measure strain distribution with a high spatial resolution for a decade [15]. We have also applied the developed fiber-optic distributed sensor to load identification and damage detection in the field of SHM, especially for structures made of advanced composite materials [16][17][18]. In addition, fundamental studies have been also implemented in order to improve the applicability of them to SHM based on strain monitoring [19,20].…”