Carbon-fiber structures has many advantages over traditional materials, but special care must be taken when bonded joints are used. A crack can propagate and cause the failure of the structure. The presence of a crack and its length can be monitored in example by means of backface strain measurements. In this work the backface technique is applied by using an array of 10 Fiber Bragg Grating (FBG) sensors applied on a carbon-fiber bonded joint. This is an interesting solution because these sensors can be embedded in carbon-fiber structures nearly without producing a load effect thanks to their small cross section. Special care must be used with FBG sensors because the expected strain profile is non-homogeneous (computed using a FEM analysis) and the FBG spectra can be altered and prevented from correct measurements (simulations using a T-matrix model were conducted). The specimen was tested with a pulsating tensile force, so that a crack developed and propagated below the optical sensors. The comparison of the observed crack position and the one inferred from the measured position of the minimum of the longitudinal strain pattern showed a good correlation, with errors lower than 10% except a small range where a 20% error was observed.

Date Published: 17 October 2012
PDF: 4 pages
Proc. SPIE 8421, OFS2012 22nd International Conference on Optical Fiber Sensors, 84214Y (17 October 2012);

Published in SPIE Proceedings Vol. 8421:
OFS2012 22nd International Conference on Optical Fiber Sensors
Yanbiao Liao; Wei Jin; David D. Sampson; Ryozo Yamauchi; Youngjoo Chung; Kentaro Nakamura; Yunjiang Rao, Editor(s)