Magdalena Mieloszyk

Application of fibre Bragg grating sensors for structural health monitoring of an adaptive wing

This paper presents the concept of application of fibre Bragg grating (FBG) sensors for structural health monitoring (SHM) of an adaptive wing. In this concept, the shape of the wing is controlled and altered due to the wing design and the use of integrated shape memory alloy (SMA) actuators. FBG sensors are great tools for controlling the condition of composite structures due to their immunity to electromagnetic fields as well as their small size and weight. They can be mounted onto the surface or embedded into the wing skin without any significant influence on the wing strength. In the first part of the paper a determination of the twisting moments produced by activation of the SMA actuators is presented. As a first step, a numerical analysis using a finite element method (FEM) commercial code ABAQUS® is presented. Then a comparison between strain values measured by FBG sensors and determined numerically is used for determination of the real value of the activation moment of every SMA actuator. Two types of damage scenarios are analysed and discussed in the paper. The first scenario is reduction of the twisting moment values produced by one of the SMA actuators. The second scenario is outer skin damage. In both damage scenarios, a neural network is used for damage detection and localization.

An adaptive wing for a small-aircraft application with a configuration of fibre Bragg grating sensors

In this paper a concept of an adaptive wing for small-aircraft applications with an array of fibre Bragg grating (FBG) sensors has been presented and discussed. In this concept the shape of the wing can be controlled and altered thanks to the wing design and the use of integrated shape memory alloy actuators. The concept has been tested numerically by the use of the finite element method. For numerical calculations the commercial finite element package ABAQUS® has been employed. A finite element model of the wing has been prepared in order to estimate the values of the wing twisting angles and distributions of the twist for various activation scenarios. Based on the results of numerical analysis the locations and numbers of the FBG sensors have also been determined. The results of numerical calculations obtained by the authors confirmed the usefulness of the assumed wing control strategy. Based on them and the concept developed of the adaptive wing, a wing demonstration stand has been designed and built. The stand has been used to verify experimentally the performance of the adaptive wing and the usefulness of the FBG sensors for evaluation of the wing condition.

Practical Application of Monitoring System Based on Optical Sensors for Marine Constructions

The paper presents structural health monitoring (SHM) system, dedicated to marine structures. The considered system is based on the fibre optic technique with Fibre Bragg Grating (FBG) sensors. The aim of this research is recognition of possible practical applications of the fibre optic techniques in selected elements of marine structures. SHM and damage detection techniques have a great importance (economical, human safety and environment protection) in the wide range of marine structures, especially for ships and offshore platforms. In the paper monitoring system of the Horyzont II and Dar Młodzieży ships and offshore oil platform is presented. Practical implementation of safety system based on optical sensors meets several difficulties. There has been installed the FBG system and its measurement results have been compared with classical techniques, e.g. piezoelectric accelerometers. The investigations have been performed for undamaged and damaged structure. Different types of failures have been modelled and tested. Damage detection ability has been specifying on the base of static and dynamic structural characteristics.

An application of neural network for Structural Health Monitoring of an adaptive wing with an array of FBG sensors

This paper presents an application of neural networks to determinate the level of activation of shape memory alloy actuators of an adaptive wing. In this concept the shape of the wing can be controlled and altered thanks to the wing design and the use of integrated shape memory alloy actuators. The wing is assumed as assembled from a number of wing sections that relative positions can be controlled independently by thermal activation of shape memory actuators. The investigated wing is employed with an array of Fibre Bragg Grating sensors. The Fibre Bragg Grating sensors with combination of a neural network have been used to Structural Health Monitoring of the wing condition. The FBG sensors are a great tool to control the condition of composite structures due to their immunity to electromagnetic fields as well as their small size and weight. They can be mounted onto the surface or embedded into the wing composite material without any significant influence on the wing strength. The paper concentrates on analysis of the determination of the twisting moment produced by an activated shape memory alloy actuator. This has been analysed both numerically using the finite element method by a commercial code ABAQUS® and experimentally using Fibre Bragg Grating sensor measurements. The results of the analysis have been then used by a neural network to determine twisting moments produced by each shape memory alloy actuator.

Frequency Domain Decomposition performed on the strain data obtained from the aluminium model of an offshore support structure

This paper presents an application of Fibre Bragg Grating (FBG) sensors for Structural Health Monitoring (SHM) of offshore wind energy support structure model. The analysed structure is a tripod equipped with 16 FBG sensors.From a wide variety of Operational Modal Analysis (OMA) methods Frequency Domain Decomposition (FDD) technique is used in this paper under assumption that the input loading is similar to a white noise excitation. The FDD method can be applied using different sets of sensors, i.e. the one which contains all FBG sensors and the other set of sensors localised only on a particular tripods leg. The cases considered during investigation were as follows: damaged and undamaged scenarios, different support conditions. The damage was simulated as an dismantled flange on an upper brace in one of the tripod legs. First the model was fixed to an antishaker table and investigated in the air under impulse excitations. Next the tripod was submerged into water basin in order to check the quality of the measurement set-up in different environmental condition. In this case the model was excited by regular waves.

Damage assessment in composite beam using infrared thermography, optical sensors and terahertz technique

Composite materials find wide ranging applications due to their high strength-to-weight ratio. Due to this increasing dependence on composite materials there is a need to study their mechanical behavior in case of damage. There are several ENDT and SHM methods for the assessment of the mechanical properties each with their set of advantages and disadvantages. The paper presents a comparative study of three distinct damage detection methods (infrared thermography, neutral axis method based on optical strain sensor measurements and terahertz spectroscopy) for the detection of delamination and temperature induced damage in a simple GFRP beam-like structure. The terahertz spectroscopy is a specialized technique suitable for detecting deterioration inside the structure, but has limited application for in-service performance monitoring. Similarly the infrared thermography technique in the active domain may be used for in situ monitoring but not in in-service assessment. Both methods allow the visualization of the internal structure and hence allow identification of the type and the extent of damage. Fibre optic sensors (especially FBG) due to their small diameter and no need of calibration can be permanently integrated within the sample and applied for continuous dynamic strain measurements. The measured strain is treated as an input for neutral axis (NA) method, which as a damage sensitive feature may be used for in-service monitoring but gives absolutely no information about the type and extent of damage. The results for damage detection based on proposed comparative studies give a complete description of the analyzed structure.

Assessment of delamination in composite beam using infrared thermography, optical sensors and terahertz technique

Composite materials find wide ranging applications due to their high strength-to-weight ratio. Due to this increasing dependence on composite materials there is a need to study their mechanical behavior in case of damage. There are several ENDT and SHM methods for the assessment of the mechanical properties each with their set of advantages and disadvantages. The paper presents a comparative study of three distinct damage detection methods (infrared thermography, neutral axis method based on optical strain sensor measurements and terahertz spectroscopy) for the detection of delamination in a simple GFRP beam-like structure. Each of the methods have their own set of advantages and disadvantages. The terahertz spectroscopy is a specialized technique suitable for detecting deterioration inside the structure, but is not suitable for in performance monitoring. Similarly the infrared thermography technique in the active domain may be used for in situ monitoring but not in in-service assessment. Both methods allow the visualization of the internal structure and hence allow identification of the type and the extent of damage. Fibre optic sensors (especially FBG) due to their small diameter and no need of calibration can be permanently integrated within the sample and applied for continuous dynamic strain measurements. The measured strain is treated as an input for neutral axis (NA) method, which as a damage sensitive feature may be used for in-service monitoring but gives absolutely no information about the type and extent of damage. The results for damage detection based on proposed comparative studies give a complete description of the analyzed structure.

Experimental investigation of thermal characteristics of synthetic jet generator's diaphragm with piezoelectric actuator

An experimental analysis of the thermal characteristics of two different diaphragms of the synthetic jet generator was presented in this paper. It is extremely important to study temperature characteristics of the components with piezoelectric actuators working in various modes. Often piezoelectric actuators are used aiming to obtain maximum displacements that are possible when a piezoelectric actuator operates under maximum excitation voltage and often at the first resonance frequency. The theory suggests that working in such modes extremely increases temperature of the piezoelectric elements and it can reach maximum point. High temperatures might cause deformation or other changes of mechanical properties of the other components. This might influence the life time and operational characteristics of the synthetic jet generator. The main task of this work was to find the best working conditions for the synthetic jet generator. Dynamic characteristics of the diaphragm with piezoelectric material were measu...

Composite samples with different contaminations analysed with THz spectrometry

Composite elements are recently commonly used in many industrial branches like aviation, marine or civil engineering. One of the problems that can influence on material durability are contaminations (e.g. water, oil, dust) that can be introduced into elements structure during manufacturing process or can diffuse into its internal part during exploitation. Such intrusions locally change material characteristics, affect its durability and can be a damage origin significantly decreasing mechanical properties of a composite object. Due to this it is important to have a non-destructive method to inspect an internal structure of elements just after manufacturing or in intervals during its exploitation. One of the techniques is THz spectroscopy that can be applied for non-conductive materials. This method can be used for identification of discontinuities or material structural disintegrations that results in changes of absorption, refractive index or scattering of THz waves propagating throughout the material structure. The paper presents an application of THz spectroscopy for detection and localization of different contaminations (like water, oil or dust) that were introduced into composite material during its manufacturing process or were an effect of exploitation faults. During analysis the limitations of proposed method will be determined.

Multi-rosettes sensing analysis for an impact assessment in composite plate-like structure

Advanced composite materials have gained popularity in high-performance structural designs applications that require light weight components with superior mechanical properties in order to perform in demanding service conditions as well as provide energy efficiency and safety to mankind and nature. Damage can appear by external impacts or internal failures. The structural damage can occur due to many factors which are difficult to predict in advance, e.g.: sudden impact loads. An external impact can cause an internal damage with no visible marks on the external surfaces of the element. The possible hidden damage can be the source of a further mechanical deterioration of the composite structural element. Recently one of the promising monitoring method is based on Fiber Bragg Grating (FBG) sensors. It is due to the advantages of FBG sensors such as small size and weight, high corrosion resistance or no calibration requirements. Also it is very easy to multiplex FBG sensors and make rosettes arrays that can be implemented on/ into structures. The goal of the research is to analyse impact detection capability of different FBG strain rosettes types. Additionally the sensitivity and area of working of an individual rosette will be considered. The experiment will be carried out on a sandwich plate with the use of impact hammer. The proposed impact detection method by a rosette network can be applied on structures like plane wings, turbine blades or ship masts. The locations of detected impacts can be further analysed by more sophisticated method (terahertz spectroscopy or infrared thermography).