Curing quality monitoring and loading detection of composite structures with embedded capacitive sensor array

In this paper, we discuss the dynamics of beams with multiple delaminations. The objective of the study is to use the dynamic response of the delaminated beams in health monitoring of composite structures. As a first step, we present experimental results on the vibrations of a cantilever beam with multiple delaminations. These experiments are conducted by exciting the beam with piezoelectric actuators. The response is detected by using a high-speed video camera to study the existence of delamination opening modes in a beam with multiple delaminations. Then, an analysis of natural frequencies and mode shapes, for a delaminated beam, is presented by using analytical techniques. The measured dynamic responses of the beam with multiple delaminations are also presented. The experimentally detected nonlinear response is discussed. Introduction Delaminations or interlayer cracks and impact damages are typical defects observed in composite structures. The presence of these defects changes the dynamic characteristics of the structure . Some of the specific changes in the observed dynamic characteristics include changes in natural frequencies, changes in the mode shapes and changes in damping ratios. These changes can be used to identify the existence, location and magnitude of a delamination or an impact damage, before they can grow to their critical sizes. Studies, to date, are concerned with the dynamics of beams and plates with a single delamination. In this paper, we specifically discuss the structural dynamics of a beam with multiple delaminations. This information can be used to develop health-monitoring techniques for composite beams with multiple delaminations. In an earlier paper, Luo and Hanagud studied the effects of defects, like saw-cuts, impact damage and delamination, on the structural dynamic characteristics of composite beams. They have shown that perturbations in natural frequencies and modes of a beam, due to defects, can be used for health monitoring of structures. In particular, it has been shown that an integral equation that considers perturbations in curvature modes and natural frequencies can be very effectively used to detect local defects. To distinguish delaminations from other types of monitored (identified) defects Luo and Hanagud have discussed nonlinear effects like superharmonic response in the dynamic response of a harmonically excited delaminated beam. They considered only a single delamination. In this paper we study beams with multiple delaminations. More specifically, we discuss dynamic response and the changes in natural frequencies, mode shapes due to multiple delaminations in a composite beam. One of the earliest models for vibration analysis of composite beams with delaminations was proposed by Ramkumar et al. This model simply used four Timoshenko beams connected at the delamination edges to model a composite beam with one throughwidth delamination. The predicted frequencies, based on this model, were consistently lower than the results of experimental measurements. Wang et al. improved the analytical solution by including coupling between flexural and axial vibrations of the delaminated sublaminates. Using an isotropic beam with splits and the classical beam model, they found that the calculated natural frequencies were closer to experimental results. With similar considerations, Nagesh Gummadi and Hanagud formulated a finite element solution for arbitrary composite beams. In the finite element models, they considered a classical composite beam model as well as the beam model with high order shear deformations. Mujumdar and Suryanarayan have proposed a model which imposed a constraint between the delaminated sublaminates to force them to have the same flexural displacement. This model was unable to * Ph.D. Student, School of Aerospace Engineering † Professor, School of Aerospace Engineering, AIAA Member Copyright © 1999 The American Institute of Aeronautics and Astronautics Inc. All rights reserved

This study introduces an enhanced formulation of the Particle Inverse Method (PIM) tailored for shape sensing and crack propagation monitoring of laminated composite plates. Building upon the foundational concept of PIM as a novel particle-based structural health monitoring method for isotropic plates, the approach presented herein enables full-field deformation reconstruction and real-time crack propagation monitoring of laminated composite plates from discrete strain measurements, without requiring knowledge of loading conditions or material properties. The method utilizes a mesh-free particle discretization and a nonlocal differential operator inspired by peridynamics to approximate spatial gradients of the displacement field. Through a variational least-squares principle, the algorithm minimizes discrepancies between numerically reconstructed strains and experimental strain data obtained via distributed sensors. A damage parameter is defined based on bond-level interactions to capture the initiation and progression of cracks in composite plates. The proposed framework supports continuous assessment even as damage evolves. The performance of the method is demonstrated through numerical and experimental case studies on composite laminates with various ply configurations and crack orientations. Results confirm the method’s capability to accurately reconstruct full-field displacements while predicting crack opening and propagation behavior, validating its potential for real-time health monitoring of composite structures.

Νέα προσέγγιση στην παρακολούθηση της αναπτυσσόμενης βλάβης υπό μηχανική φόρτιση σε ινώδη σύνθετα υλικά με μήτρα ενισχυμένη με νανοσωληνίσκους άνθρακα

Damage quantification in composite laminates based on sparsity-difference estimation of the normal time–frequency representation

This project has been partially based on a work produced by Dr. Hamed Yazdani Nezhad and his partners, entitled "Numerical Analysis of Low Velocity Rigid Body Impact Response of Composite Panels." This report has gone through the reverse finite element analysis (FEA), simulating an experimental process involving measuring the damage caused by a body impacting a composite panel at low velocity. It has shown that a numerical simulation of an experimental procedure involving composite materials can produce an accurate representation/prediction of the experimental results. Using this assumption, the following project has been carried out.Presuming that a composite laminate's structural integrity may be difficult to monitor without using invasive methods, a procedure requiring only visual surface data would be a major advancement in the structural health monitoring (SHM) of composite panels. Therefore, the purpose of this research was to explore the use of virtual technologies like AR or XR and question the validity of their use in the SHM of composite structures. Using photogrammetry and light detection and ranging (LiDAR), a composite panel's three-point bend deformation was measured, through which a three-dimensional (3D) model was created and analysed.This study has shown that the use of LIDAR is superior to that of photogrammetry for capturing surface data of a flat composite panel. Although a MATLAB® code computing the stresses and strains of the panel from the surface deformation data was unable to be implemented, an Abaqus simulation was used to provide the required relationships. The latter was used to be visualized through AR using the Unity 3D Engine. If explored further, the use of surface scanning and AR visualisation of computed data from said surface scanning can indeed revolutionise the SHM of composites.

With the growing size of large-scale structures, composite materials are being increasingly used due to their high strength-to-weight ratio. As structures get larger, so too does the necessity for a robust health monitoring system; a well-founded and reliable method of doing so is by monitoring acoustic emissions. However, such a method encounters significant problems when employed on composite structures; such as high dispersion of extensional modes, propagation distance-dependent wave velocity and highly subjective characteristic frequencies of failure modes. Ultrasonic guided waves offer the abilities of location and severity detection to a more accurate level, whereas acoustic emission involves a more efficient passive approach. By analysis of ultrasonic waves in a carbon-fibre-reinforced-polymer (CFRP) plate, information is show here that will provide the stepping stones for the development of a robust health monitoring system for composite structures using ultrasonic guided waves. Advanced signal processing is used to show information on selected features of an acoustic burst as it propagates through the composite material, as well as how damage affects these features. It was found that both the energy of the burst and the first asymmetric mode are affected by the orientation of fibres in a composite, although in differing ways. However, the time of flight of an acoustic burst is unaffected. Subsequently, damage affects all of the above mentioned features, and this knowledge can be utilised to identify damage. Finally, the one-dimensional propagation of a wave along the length of the fibres is tested against various statistical-based models to showcase the potential of this method for use in modelling the propagation of an acoustic wave in a composite material.

Composite structures are strong and light weight, and have great potential in enhancing the structural strength of Unmanned Air Vehicles (UAVs). In this research, we present some preliminary results of structural health monitoring (SHM) for composite structures using an unpowered wireless ultrasound system. First, we have built a testbed, which consists of ultrasonic sensors, composite specimens, and data acquisition electronics. Second, we have performed extensive experiments to collect data. An 8-sensor array was used to detect and localize defects in composite plates. Third, we have implemented defect detection and localization algorithms. We have shown that, with an 8-sensor array, we can detect and localize small defects. Fourth, we have performed an experiment to demonstrate that wired and wireless data matched well both in time domain and in frequency domain.

Aircraft smart skin technology requires the integration of large-scale, lightweight, and integrative sensor networks with aircraft structural skin, but it is difficult to directly manufacture such sensor networks in a large-scale, low-cost, reliable, and simple way. To study this issue, a design and manufacturing method of a stretchable and large-scale guided wave sensor network is proposed in this article. The key principle of the method is to design and manufacture the guided wave sensor network in a limited scale and expand it in a large-scale for aircraft smart skin of structural health monitoring. To ensure the excellent stretchability of the network, the design method of a serpentine-based fractal island-interconnect structure combined with the flexible printed circuit manufacturing process is proposed. The whole manufacturing process of the guided wave sensor network is realized by the mature flexible printed circuit process and the piezoelectric transducers (referred to as PZTs) are integrated with the network by reflow soldering which is compatible with the flexible printed circuit process, which greatly reduce manufacturing costs, simplify manufacturing process, and improve the yield and stability of the network. The guided wave sensor network can be uniaxially stretched to 500% of its original size and work well when fully expanded to cover 2500% of its original area. The test results of guided wave response show that the PZTs on the network can excite and receive guided wave signal normally. In addition, the network is placed on the surface of a carbon fiber composite laminate with stiffeners and the validation results show that the network can be applied to both active and passive guided wave–based structural health monitoring of composite structures, including damage imaging and impact imaging.

In-service health monitoring of composite structures : Proceedings of the 1990 SEM Spring Conference on Experimental Mechanics, Albuquerque, New Mexico (United States), 4–6 Jun. 1990. pp. 304–309. Society for Experimental Mechanics (1990)

Many composite materials and structures are susceptible to defects, which can significantly reduce the strength of structures and may grow to failure. To avoid the catastrophic failure of structures, development of a reliable method of structural health monitoring is one of the most important keys in maintaining the integrity and safety of structures. Dynamic response-based damage detection offers a simple procedure as an alternative to the conventional nondestructive evaluation techniques. However, this technique depends on the quality of measured data for its identification accuracy. In this article, experimental aspects of dynamic response-based damage detection technique on carbon/ epoxy composites are addressed. Smart piezoelectric materials are used as sensors or actuators to acquire the curvature modes of structures. These materials are surface-bonded to the beams. An impulse hammer is used as an actuating source as well. Four types of damage detection algorithms are evaluated for several possible damage configurations with two different excitation sources. The quality of damage identification with the four different detection algorithms is discussed. These experimental damage identification techniques using curvature modes and piezoelectric materials can be effectively used in damage detection and health monitoring of composite structures.

This paper proposes a dense spray-coating active sensing arrays for composite structural health monitoring via the guided wave control. The actuation-sensing capability is realized by integrating piezoelectric nano-powder into a hosting matrix, followed by the formation of an active material layer on the composite surface through a spraying process. The actuation and sensing of guided wave mode can be achieved through the optimization of electrode configuration, in conjunction with dispersion effect. This research initiates with the analysis of the dispersion curves of composites to determine electrode parameters. Subsequently, three-dimensional numerical models in several array patterns, such as inter-digital type, comb types and irregular annular array, are meticulously constructed. Single-mode generation at one direction is achieved through the spatial distribution of array electrodes coupled with wavelength modulations in inter-digital array and comb array. At the same time, omnidirectional single-mode generation of irregular annular array is conducted through the electrode spatial distribution coupled with all direction wavelength modulations. Ultimately, the guided wave control performance is numerically investigated through exciting an anti-symmetric and a symmetric type guided wave mode in a multilayer composite plate. The numerical simulation shows that the proposed spray-coating system possesses great potential for future composite damage detection applications. The paper finishes with summary, concluding remarks, and suggestions for future work.

Specific characteristics of Lamb waves, and more particularly their ability to propagate over long distances, make them a promising technique for health monitoring of composite structures using piezoelectric transducers bonded on the surface or embedded inside the material. In order to evaluate the possibilities of the technique, a theoretical dispersion model for the Lamb waves propagation has been realized for a carbon-epoxy composite material, and the control parameters, incidence angle, emission mode and frequency, have been fixed. The technique has then been experimented in a transmission mode with contact conversion mode transducers. The propagation over long distance and the detection of delaminations have been put in evidence. Then, optimized transducers have been manufactured in order to instrument, first, monolithic composite structures using surface bonding, and second, sandwich structures with embedded elements in the bulk. Experimental results show that a large network could be envisaged. This technique presents serious interests compared to conventional ultrasonic techniques, testing at a point, or passive measurements of local stress and strain modifications due to the delamination.

Structural health monitoring (SHM) of aircraft composite structure is helpful to increase reliability and reduce maintenance costs. Due to the great effectiveness in distinguishing particular guided wave modes and identifying the propagation direction, the spatial-wavenumber filter technique has emerged as an interesting SHM topic. In this paper, a new scanning spatial-wavenumber filter (SSWF) based imaging method for multiple damages is proposed to conduct on-line monitoring of aircraft composite structures. Firstly, an on-line multi-damage SSWF is established, including the fundamental principle of SSWF for multiple damages based on a linear piezoelectric (PZT) sensor array, and a corresponding wavenumber-time imaging mechanism by using the multi-damage scattering signal. Secondly, through combining the on-line multi-damage SSWF and a PZT 2D cross-shaped array, an image-mapping method is proposed to conduct wavenumber synthesis and convert the two wavenumber-time images obtained by the PZT 2D cross-shaped array to an angle-distance image, from which the multiple damages can be directly recognized and located. In the experimental validation, both simulated multi-damage and real multi-damage introduced by repeated impacts are performed on a composite plate structure. The maximum localization error is less than 2 cm, which shows good performance of the multi-damage imaging method. Compared with the existing spatial-wavenumber filter based damage evaluation methods, the proposed method requires no more than the multi-damage scattering signal and can be performed without depending on any wavenumber modeling or measuring. Besides, this method locates multiple damages by imaging instead of the geometric method, which helps to improve the signal-to-noise ratio. Thus, it can be easily applied to on-line multi-damage monitoring of aircraft composite structures.

Effects of composite lamina properties on fundamental Lamb wave mode dispersion characteristics

Fiber-optic ultrasonic sensing systems have been developed for structural health monitoring of composite structures by introduction of phase-shifted fiber Bragg gratings (PS-FBGs). The systems can achieve the compatibility of high sensitivity and broadband performance. First, PS-FBG balanced sensing system was developed and succeeded in detection of small acoustic emission signals of composite laminates. Next, erbium fiber ring laser sensing system with inbuilt PS-FBG was developed. This system has high robustness due to its self-adjustment function for environmental disturbances and achieved much higher sensitivity and ultra-broadband respondency than piezoelectric ceramic sensors. These systems have large potential to realize the ultrasonic SHM.