PSI - Issue 28

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ScienceDirect

Procedia Structural Integrity 28 (2020) 1473–1480 Structural Integrity Procedia 00 (2020) 000–000 Structural Integrity Procedia 00 (2020) 000–000

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© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo Abstract This paper investigates a strain-based structural health monitoring (SHM) method for damage detection and propagation assessment in composite sandwich structures. As case example, an idealized Airbus A-340 spoiler is considered. Critical failure modes of such sandwich structures composed of fiber reinforced polymer (FRP) face layers and a honeycomb core are, e.g., face layer delamination and debonding from the core. The latter challenges today’s non-destructive evaluation methods, and thus, shall be addressed in the present work. For investigation an idealized spoiler model in the scale 1:2 composed of glass fiber reinforce polymer (GFRP) face layers and a honeycomb core is considered. The damage assessment is realized by static strain measurements along so-called zero-strain trajectories (ZST) at the loaded structure. A zero-strain direction exists for every spatial strain state with major strain directions with opposite signs (tensile and compression). Connecting zero-strain directions at various points of a structure yields a ZST. This allows the monitoring of a ZST by, e.g., a distributed fiber optical sensor (FOS) or fiber Bragg grating sensors (FBG). However, for the undamaged pristine state and defined loading there would be no strain measured along these trajectories. A structural change, i.e., damage initiation and propagation would influence the strain state and therefore yield a strain value along the ZST of the pristine structure. Consequently, strain measurements along a ZST represent a most sensible feature for damage assessment. The work investigates the use of strain measurements along ZST for the monitoring of debonding initiation and propagation at the edge of the spoiler model sandwich structure by means of numerical and experimental analysis. The considered face layer debonding is semicircular and located at the trailing edge of the idealized spoiler. For damage propagation analysis it is increased step-by-step. As load case, a true wind-load condition of the A-340 spoiler is considered. An in-depth numerical FEM investigation is performed to calculate the ZST for the pristine structure and the changes in the strain states caused by the damage. The experimental validation of the FEM model is realized by strain measurements via a digital image correlation system (DIC) at the statically loaded idealized spoiler. Finally, the possible application of strain measurements along a ZST for debonding initiation and growth will be demonstrated and its potential and issues for real online monitoring will be discussed. 2020 The Authors. Published by Elsevier B.V. T i is an open access article under the CC BY- C-ND license (http: // cr ativec mmons.org / licenses / by-nc-nd / 4.0 / ) r ie unde responsibility of the European St uctural Integr ty Society (ESIS) ExCo. Keywords: Structural Health Monitoring (SHM); Aircraft Structures; Composite; Fiber reinforced composite (FRP); Sandwich structures Abstract This paper investigates a strain-based structural health monitoring (SHM) method for damage detection and propagation assessment in composite sandwich structures. As case example, an idealized Airbus A-340 spoiler is considered. Critical failure modes of such sandwich structures composed of fiber reinforced polymer (FRP) face layers and a honeycomb core are, e.g., face layer delamination and debonding from the core. The latter challenges today’s non-destructive evaluation methods, and thus, shall be addressed in the present work. For investigation an idealized spoiler model in the scale 1:2 composed of glass fiber reinforce polymer (GFRP) face layers and a honeycomb core is considered. The damage assessment is realized by static strain measurements along so-called zero-strain trajectories (ZST) at the loaded structure. A zero-strain direction exists for every spatial strain state with major strain directions with opposite signs (tensile and compression). Connecting zero-strain directions at various points of a structure yields a ZST. This allows the monitoring of a ZST by, e.g., a distributed fiber optical sensor (FOS) or fiber Bragg grating sensors (FBG). However, for the undamaged pristine state and defined loading there would be no strain measured along these trajectories. A structural change, i.e., damage initiation and propagation would influence the strain state and therefore yield a strain value along the ZST of the pristine structure. Consequently, strain measurements along a ZST represent a most sensible feature for damage assessment. The work investigates the use of strain measurements along ZST for the monitoring of debonding initiation and propagation at the edge of the spoiler model sandwich structure by means of numerical and experimental analysis. The considered face layer debonding is semicircular and located at the trailing edge of the idealized spoiler. For damage propagation analysis it is increased step-by-step. As load case, a true wind-load condition of the A-340 spoiler is considered. An in-depth numerical FEM investigation is performed to calculate the ZST for the pristine structure and the changes in the strain states caused by the damage. The experimental validation of the FEM model is realized by strain measurements via a digital image correlation system (DIC) at the statically loaded idealized spoiler. Finally, the possible application of strain measurements along a ZST for debonding initiation and growth will be demonstrated and its potential and issues for real online monitoring will be discussed. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo. Keywords: Structural Health Monitoring (SHM); Aircraft Structures; Composite; Fiber reinforced composite (FRP); Sandwich structures 1st Virtual European Conference on Fracture Strain measurements along zero-strain trajectories as possible structural health monitoring method for debonding initiation and propagation in aircraft sandwich structures Thomas Bergmayr a, ∗ , Markus Winklberger b , Christoph Kralovec b , Martin Schagerl a,b a Christian Doppler Laboratory for Structural Strength Control of Lightweight Constructions, Johannes Kepler University Linz, 4040 Linz, Austria b Institute of Structural Lightweight Design, Johannes Kepler University Linz, 4040 Linz, Austria 1st Virtual European Conference on Fracture Strain measurements along zero-strain trajectories as possible structural health monitoring method for debonding initiation and propagation in aircraft sandwich structures Thomas Bergmayr a, ∗ , Markus Winklberger b , Christoph Kralovec b , Martin Schagerl a,b a Christian Doppler Laboratory for Structural Strength Control of Lightweight Constructions, Johannes Kepler University Linz, 4040 Linz, Austria b Institute of Structural Lightweight Design, Johannes Kepler University Linz, 4040 Linz, Austria

∗ Corresponding author. Tel.: + 43 732 2468 6664 ; fax: + 43 732 2468 6662. E-mail address: thomas.bergmayr@jku.at ∗ Corresponding author. Tel.: + 43 732 2468 6664 ; fax: + 43 732 2468 6662. E-mail address: thomas.bergmayr@jku.at

2452-3216 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo 10.1016/j.prostr.2020.10.121 2210-7843 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo. 2210-7843 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo.