Vibration-based structural interrogation and health monitoring based on nonlinear signal analysis

Vibration-based structural interrogation and health monitoring is a field which is concerned with the estimation of the current state of a structure or a component from its vibration response with regards to its ability to perform its intended function appropriately. This study suggests using the concept of signal cross-correlation for the purposes of vibration-based health monitoring. A nonlinear alternative of the cross-correlation, the mutual information between two signals measured on the structure, regarded as an input and an output, is used to develop a damage metric and a damage index. The application of the suggested methodology is shown on a composite beam test set using experimental measurements

A method for vibration-based structural interrogation and health monitoring based on signal cross-correlation

Vibration-based structural interrogation and health monitoring is a field which is concerned with the estimation of the current state of a structure or a component from its vibration response with regards to its ability to perform its intended function appropriately. One way to approach this problem is through damage features extracted from the measured structural vibration response. This paper suggests to use a new concept for the purposes of vibration-based health monitoring. The correlation between two signals, an input and an output, measured on the structure is used to develop a damage indicator. The paper investigates the applicability of the signal cross-correlation and a nonlinear alternative, the average mutual information between the two signals, for the purposes of structural health monitoring and damage assessment. The suggested methodology is applied and demonstrated for delamination detection in a composite beam

A simple method for enhanced vibration-based structural health monitoring

This study suggests a novel method for structural vibration-based health monitoring for beams which only utilises the first natural frequency of the beam in order to detect and localise a defect. The method is based on the application of a static force in different positions along the beam. It is shown that the application of a static force on a damaged beam induces stresses at the defect which in turn cause changes in the structural natural frequencies. A very simple procedure for damage detection is suggested which uses a static force applied in just one point, in the middle of the beam. Localisation is made using two additional application points of the static force. Damage is modelled as a small notch through the whole width of the beam. The method is demonstrated and validated numerically, using a finite element model of the beam, and experimentally for a simply supported beam. Our results show that the frequency variation with the change of the force application point can be used to detect and in the same time localize very precisely even a very small defect. The method can be extended for health monitoring of other more complicated structures

Vibration-based methods for structural and machinery fault diagnosis based on nonlinear dynamics tools

This study explains and demonstrates the utilisation of different nonlinear-dynamics-based procedures for the purposes of structural health monitoring as well as for monitoring of robot joints

Multivariate statistical analysis for damage and delamination in composite structures

The article is devoted to the analysis of the vibration response of composite laminates .Our aim is to develop a method for analysis of the vibration response of structures made of composites which will also be used to develop a vibration-based health monitoring procedure for such structures. Composite materials and composite laminates in particular, exhibit complex dynamic behaviour which on most occasions cannot be modelled linearly. Delamination introduces additional nonlinearities in the vibration behaviour of the structure as a result of the interrupted contact between the layers or the opening and closing of the delamination. Thus conventional linear structural dynamics methods like modal analysis cannot be applied. In this study, the vibration response signals are recorded from damaged and non-damaged (healthy) laminated composite beams. The frequency domain signals are subjected to a special type of Principal Component Analysis, known as Multichannel Singular Spectrum Analysis (MSSA). This type of analysis is known to uncover oscillation patterns and was suggested in the investigation in place of modal analysis. The idea is to establish a new feature based state-space for the vibration response signal. The response of the healthy structure is used as a baseline to which all the responses are compared. MSSA decomposes the signal into new components which are lineal combinations of the original frequency series components. The first several components are responsible for most of the variance of the original signal. The new space is with a much smaller dimension as compared to the original data and creates new variables which can be used as damage features. The results demonstrate strong potential for using MSSA for the purpose of structural health monitoring

Triboelectric sensor as a dual system for impact monitoring and prediction of the damage in composite structures

Bird strikes, hailstone impacts, and other type of mechanical collisions are quite frequent for a number of crucial and important structures, including aircrafts, wind turbines, bridges and other composites structures. These impacts harm the integrity of the composite laminates used in their structures which results in delamination and other failures which reduces their overall lifetime. Hence, the prediction of the damage induced by these impacts is of vital importance to assess the integrity of the composite structures. This paper suggests a triboelectric sensor based on polyvinyl fluoride nanofibers which is used to measure the velocity of the impacts and predict the structural integrity of the composites. For the purpose an experiment is designed where composite plates are subjected to controlled velocity impacts using a drop-weight impact machine. During the experiment, the fabricated triboelectric sensor is adhered to the composite specimens with the aim to investigate the effect of the velocity of the impacts on the sensor electric responses. Our results show that the sensor electric response increases with the increase of the impact velocity. Additionally, the produced voltage and current outputs show a linear directly proportional relationship to the measured impact velocity, which facilitates greatly the estimation of the impact velocity from the measured electric response. Furthermore, the paper also proves that the sensor electrical responses can be also used to estimate the size of the delamination caused by the impacts. The findings of this research demonstrate the potential of triboelectric sensors for impact velocity monitoring and propose a new approach to predict the damage caused by impacts in composite structures. These results are of a great interest for the industry as the delamination caused by impacts is very difficult to detect by visual inspections

A multivariate data analysis approach towards vibration analysis and vibration-based damage assessment : application for delamination detection in a composite beam

This paper introduces a novel methodology for structural vibration analysis and vibration-based monitoring which utilises a special type of Principal Components Analysis (PCA), known as Singular Spectrum Analysis (SSA). In this study the methodology is introduced and demonstrated for the purposes of damage assessment in structures using their free decay response. The method's damage assessment properties are first demonstrated on a numerical example for a two degree-of-freedom (2DOF) spring-mass and damper system with non-linear stiffness. The method is then applied to an experimental case study of a composite laminate beam. The method is based on the decomposition of the frequency domain structural variation response using new variables, the Principal Components (PCs). Only a certain number of the new variables are used to approximate the original vibration signal with very good accuracy. The presented results demonstrate the potential of the method for vibration based signal reconstruction and damage diagnosis. The healthy and the different damaged scenarios are clearly distinguishable in the new space of only two reconstructed components where a strong clustering efect is observed

Real-time diagnosis of small energy impacts using a triboelectric nanosensor

Recently, triboelectric nanogenerators (TENGs) are generating increasing interest due to their important applications as energy harvesters and self-powered active sensors for pressures, vibrations and other mechanical motions. However, there is still little research within the research community on their potential as self-powered impact sensors. This paper considers the development of a novel triboelectric nanogenerator, which is prepared using a simple and economic fabrication process based on electrospinning. Furthermore, the paper studies the changes in the generated electric response caused by small energy impacts. For the purpose, the TENG electric outputs generated by the impact of a free-falling ball dropped from different heights are investigated. The idea is to investigate the relation between the electric responses of the nanogenerator and the energy of the impact. The experimental results demonstrate that the voltage and current outputs increase linearly with the increase of the impact energy. Moreover, the electric responses of the triboelectric nanogenerator show a very high sensitivity (14 V/J) to the changes in the impact energy and good repeatability. The main achievements of this paper are in the development of novel triboelectric nanogenerator composed of polyvinylidene fluoride nanofibers and a thin film of polypropylene, and its successful application as an impact sensor for real-time assessment of small energy impacts

Vibration analysis of a circular plate in interaction with an acoustic cavity leading to extraction of structural modal parameters

When carrying out vibration health monitoring (VHM) of a structure it is usually assumed that the structure is in the absence of fluid interaction and that any environmental effects which can cause changes in natural frequency either remain constant or are negligible. In certain cases, this condition cannot be assumed and therefore it is necessary to extract values of natural frequencies of the structure for the condition with no fluid interaction from those values measured. This paper considers the case of a thin circular plate in contact with a fluid cavity giving rise to strong structural/fluid vibration interaction. The paper details the free vibration analysis of the coupled system and through consideration of modal energy, illustrates how the affined modes of vibration of the plate and the fluid can be qualitatively described. The paper then introduces a method by which the natural frequencies of the plate in the absence of fluid interaction can be obtained from those of the plate in interaction with the fluid

Nonlinear vibrations, stability, analysis and control

This paper looks at how important advances in mathematics, physics, biology, economics, and engineering science have shown the importance of the analysis of nonlinear vibrations, instabilities, and strongly coupled dynamical behavior