In-service structural health monitoring of composite aircraft structures plays a key role in the assessment of their performance and integrity. In recent years, Fibre Optic Sensors (FOS) have proved to be a potentially excellent technique for real-time in-situ monitoring of these structures due to their numerous advantages, such as immunity to electromagnetic interference, small size, light weight, durability, and high bandwidth, which allows a great number of sensors to operate in the same system, and the possibility to be integrated within the material. However, more effort is still needed to bring the technology to a fully mature readiness level. In this paper, recent research and applications in structural health monitoring of composite aircraft structures using FOS have been critically reviewed, considering both the multi-point and distributed sensing techniques.

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Fibre Optic Sensors for Structural Health Monitoring of Aircraft Composite Structures: Recent Advances and Applications.

Recent developments in finite element analysis for laminated composite plates

Modeling of impacts on composite structures

Nowadays, smart composite materials embed miniaturized sensors for structural health monitoring (SHM) in order to mitigate the risk of failure due to an overload or to unwanted inhomogeneity resulting from the fabrication process. Optical fiber sensors, and more particularly fiber Bragg grating (FBG) sensors, outperform traditional sensor technologies, as they are lightweight, small in size and offer convenient multiplexing capabilities with remote operation. They have thus been extensively associated to composite materials to study their behavior for further SHM purposes. This paper reviews the main challenges arising from the use of FBGs in composite materials. The focus will be made on issues related to temperature-strain discrimination, demodulation of the amplitude spectrum during and after the curing process as well as connection between the embedded optical fibers and the surroundings. The main strategies developed in each of these three topics will be summarized and compared, demonstrating the large progress that has been made in this field in the past few years.

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Fiber Bragg grating sensors toward structural health monitoring in composite materials: challenges and solutions.

Thermally-induced deformation behavior of unsymmetric laminates

A modified shear lag analysis, taking into account the concept of in terlaminar shear layer, is employed to predict the onset of a transverse crack and multiple transverse cracking. In this analysis, the boundary conditions are satisfied for any trans verse crack spacing. The crack multiplication is simulated by adjusting the crack spacing. Based on this analysis the laminate stiffness reduction due to the multiple transverse crack ing is also evaluated in cross-ply laminated composites. The energy concept is utilized to assess the effect of 90° layer thickness and the constraining effect of 0° layer on the trans verse cracking behavior of cross-ply laminated composites. Predictions of the onset of a transverse crack and stiffness reduction due to transverse cracks are compared with those of previous analyses and existing experimental data. The present analysis is simple, yet its results show reasonable agreement with experimental results.

Prediction of Transverse Cracking and Stiffness Reduction in Cross-Ply Laminated Composites

Effect of residual shear strain on the cured shape of unsymmetric cross-ply thin laminates

The warping analysis of the general unsymmetric laminates with arbitrary lay-up angles is still not fully understood whereas the cross-ply laminates have been characterized well. This paper presents the formulation that treats the curvatures and prin cipal direction of curvature of the cured shape in unsymmetrically laminated composites. The effect of spatial dependence of in-place strains on curvatures is significant near the bifurcation point in the case of laminates having the stacking arrangement in which snap- through phenomenon occurs. It is shown that the principal direction of curvature calculated from classical lamination theory agrees with this theory in the limited range of length-to-thickness ratios of laminate. Curvatures and principal direction of curvature ac cording to the length-to-thickness ratios, number of layers, and lay-up angles of the lami nate are presented.

Cured Shape of Unsymmetric Laminates with Arbitrary Lay-Up Angles

Effect of transverse cracks on the thermomechanical properties of cross-ply laminated composites

A new method for simple prediction of the impact force history on composite laminates subjected to low-velocity impact is proposed. First, the impact force history is calculated from the impact response analysis using the finite element method incorporated with the modified Hertzian contact law. Frequency characteristics of the numerical impact force history are investigated from modal analysis and compared with the natural frequencies of the system in which the mass of an impactor is lumped with the plate. The present method can be efficiently applied to isotropic or orthotropic plates with unknown contact laws as well as composite laminates with no restraint on the material properties and the geometrical shape

Chang Sun Hong

Papers

Prediction of Transverse Cracking and Stiffness Reduction in Cross-Ply Laminated Composites

Effect of residual shear strain on the cured shape of unsymmetric cross-ply thin laminates

Cured Shape of Unsymmetric Laminates with Arbitrary Lay-Up Angles

Effect of transverse cracks on the thermomechanical properties of cross-ply laminated composites

New approach for simple prediction of impact force history on composite laminates