Strain-based health indicators for the structural health monitoring of stiffened composite panels

Abstract

A common defect of composite-stiffened structures is the disbond at the interface between the two constituents (skin/stringer), as a result of inefficient manufacturing process or foreign object impacts in service. Generally, discontinuities within the volume of an elastic solid medium, subjected to mechanical load, cause anomalies on the strain field in the near vicinity of the discontinuity. Utilizing this observation, this work investigates the effect of artificially induced disbonds in the skin/stiffener interface of an aeronautical-grade generic element. A structural health monitoring methodology is developed, leveraging on numerically simulated strains along the stringer foot which aims to assess the health state of the panel as the size of the disbonds increases. The study is implemented using a parametric finite element model generating various disbond scenarios. Longitudinal strain values are acquired at the exact points where in reality actual fiber Bragg grating sensors will be located. Two types of commonly utilized strain-based health indicators are evaluated, and their drawbacks are revealed and discussed. A new health indicator is proposed that proves its capability to monitor growing disbonds while being both load- and baseline-independent.

Health Monitoring of Aerospace Structures Utilizing Novel Health Indicators Extracted from Complex Strain and Acoustic Emission Data

“…Several HIs for both constant and variable amplitude fatigue were developed and their performance was presented throughout fatigue tests. The strain-based HIs, i.e., HI 1 and HI 2 , were used in [7] to successfully detect damage in quasi-static numerical tests. The HIs investigated in the present work are intended for diagnostic and prognostics tasks in which monotonic trends are highly desirable; hence, the proposal of the fused HIs.…”

“…Even looking at the same sensor on two different specimens, it is not guaranteed that the behavior will be similar because the buckling modes may also affect the local behavior. However, this HI can provide useful information regarding the damage progression, as seen in [7], by successfully monitoring disbond growth. It is worth pointing out that HI 2 curves start to diverge when damage becomes significant.…”

“…The first proposed HI was previously used in [7,36]. In these works, HI 1 was tested on data from both QS simulations conducted in a FEM and experiments.…”

“…FOS, particularly Fiber Bragg Gratings (FBGs), have attracted the interest of numerous researchers and applied to various fields. Milanoski and Loutas [7] numerically studied a composite single-stringer panel with the use of virtual FBGs. They developed strain-based health indicators (HIs) for skin-stiffener disbond monitoring.…”

Leakage detection of water pipelines based on active thermometry and FBG based quasi-distributed fiber optic temperature sensing

“…The active thermometry, which operates in such a way that a heat pulse is introduced and the temperature response is measured simultaneously, is effective in determining thermal properties such as thermal resistivity, thermal diffusivity, specific heat, and soil water content (Bristow, 1998;Freifeld et al, 2008;Krishnaiah et al, 2004). On the other hand, distributed fiber optic sensing (DFOS) techniques have been widely employed for structural health monitoring of various structures due to their unique advantages, such as small profile, flexible shape, high sensitivity, immunity to electromagnetic interference, distributed and long distance monitoring capability (Fan et al, 2019;Gu¨emes et al, 2010;Li et al, 2004;Li and Wu, 2007;Milanoski and Loutas, 2020;Villalba and Casas, 2013;Yeager et al, 2018). It has been demonstrated that the active thermometry, when instrumented with the distributed fiber optic temperature sensing techniques, presents promising application capability in the field of SHM, such scour monitoring and free span detection of subsea pipeline (Zhao et al, 2012(Zhao et al, , 2013a(Zhao et al, , 2013b(Zhao et al, , 2015, rebar corrosion detection in reinforced concrete (Li et al, 2016), and liquid level monitoring of producing oil wells (Peng et al, 2014).…”