{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,9]],"date-time":"2026-05-09T11:47:22Z","timestamp":1778327242260,"version":"3.51.4"},"reference-count":30,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2020,3,17]],"date-time":"2020-03-17T00:00:00Z","timestamp":1584403200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The increasing utilization of carbon fiber reinforced plastic (CFRP) in the aeronautical industry calls for a structural health monitoring (SHM) system for adhesively bonded CFRP joints. Optical glass fiber with inscribed fiber Bragg gratings (FBGs) is a promising technology for a SHM system. This paper investigates the intrusive effect of embedding optical glass fibers carrying FBGs on adhesive bond strength and adhesive layer thickness and quality. Embedding the optical glass fibers directly in the adhesive bond has the advantage of directly monitoring the targeted structure but poses the risk of significantly reducing the bond strength. Optical glass fibers with different cladding diameters (50, 80, 125 \u00b5m) and coating types (polyimide, with a thickness of 3\u22128 \u00b5m, and acrylate, with a thickness of ~35 \u00b5m) are embedded in structural and repair film adhesives here. Without embedded optical glass fibers, the film adhesives have an adhesive layer thickness of ~90 \u00b5m (structural) and ~100 \u00b5m (repair) after curing. The intrusive effect of the fiber embedding on the adhesive bond strength is investigated here with quasi static and fatigue single lap joint (SLJ) tensile shear tests. Also, the influence of hydrothermal aging procedures on the quasi static tensile shear strength is investigated. It is found that optical glass fibers with a total diameter (glass fiber cladding + coating) of ~145 \u00b5m significantly reduce the quasi static tensile shear strength and increase the adhesive layer thickness and number of air inclusions (or pores) in the structural film adhesive joints. In the repair adhesive joints, no significant reduction of quasi static tensile shear strength is caused by the embedding of any of the tested fiber types and diameters. However, an increase in the adhesive layer thickness is detected. In both adhesive films, no effect on the quasi-static tensile shear strength is detected when embedding optical glass fibers with total diameters &lt;100 \u00b5m. The applied aging regime only affects the repair film adhesive joints, and the structural film adhesive joints show no significant reduction. A polyimide-coated 80 \u00b5m optical glass fiber is selected for fatigue SLJ tensile shear tests in combination with the more sensitive structural film adhesive. No significant differences between the S-N curves and tensile shear fatigue strength of the reference samples without embedded optical fibers and the samples carrying the polyimide-coated 80 \u00b5m optical glass fibers are detected. Thus, it is concluded that the influences of embedding optical glass fibers with total diameters &lt;100 \u00b5m on the fatigue limit of the tested film adhesive joints is negligible.<\/jats:p>","DOI":"10.3390\/s20061665","type":"journal-article","created":{"date-parts":[[2020,3,18]],"date-time":"2020-03-18T08:20:44Z","timestamp":1584519644000},"page":"1665","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":17,"title":["Influence of Embedding Fiber Optical Sensors in CFRP Film Adhesive Joints on Bond Strength"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3601-7520","authenticated-orcid":false,"given":"Neele","family":"Grundmann","sequence":"first","affiliation":[{"name":"Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Wiener Stra\u00dfe 12, 28359 Bremen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hauke","family":"Br\u00fcning","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Wiener Stra\u00dfe 12, 28359 Bremen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Konstantinos","family":"Tserpes","sequence":"additional","affiliation":[{"name":"Laboratory of Technology &amp; Strength of Materials, Department of Mechanical Engineering &amp; Aeronautics, University of Patras, Patras 26500, Greece"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tim","family":"Strohbach","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Wiener Stra\u00dfe 12, 28359 Bremen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Bernd","family":"Mayer","sequence":"additional","affiliation":[{"name":"University of Bremen, Faculty of Production Engineering, 28359 Bremen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,3,17]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"342","DOI":"10.1016\/j.paerosci.2010.05.001","article-title":"Structural health monitoring techniques for aircraft composite structures","volume":"46","author":"Diamanti","year":"2010","journal-title":"Prog. 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