Macro Fiber Composite Sensors Research Articles

Fracture resistance of in-situ healed CFRP composite using thermoplastic healants

In this study, macro fiber composite (MFC) assisted in-situ healing of unidirectional fiber reinforced polymer (FRP) composite was investigated and characterized by the double cantilever beam (DCB) tests. Biomimetic healing of delamination damage in carbon fiber reinforced composite (CFRP) was achieved by using a blend of biphasic healant: polycaprolactone (PCL) and polyurethane shape memory polymer (SMP). When the damage initiated at the fiber matrix interface or through the matrix, the thermoplastic SMP/PCL blend closed the crack due to localized stimulus (heat) provided by MFC. Crack closure was followed by healing via PCL healant using the same stimulus. Protocol for characterizing the healing efficiency of CFRP composite was established. The experimental results demonstrated that the localized healing method not only enables the in situ healing but also outperforms conventional healing methods in terms of healing efficiency. The MFC actuated healing yielded up to ∼160 % recovery of virgin interlaminar fracture property and ∼70 % flexure property recovery for seven healing cycles. This novel healing system can thus provide efficient in-situ healing in aerospace structures using MFC sensors as self-healing actuators, and bridge the gap between the laboratory scale and large-scale industrial application of self-healing polymer composite.

Applications of piezoelectric MFC type transducers in mechatronic measurement systems - the impact of a mechanical subsystem damage on a system operation

The work include a report of research works concerning applications of non-classical piezoelectric transducers in mechatronic measuring systems. Composite piezoelectric transducers called Macro Fiber Composite (MFC) are considered. Characteristics of considered transducers were made, indicating their advantages and disadvantages, as well as the results of carried out laboratory tests are presented, in which MFC transducers were used as sensors for mechatronic measurement systems. A series of laboratory tests was carried out on the created laboratory stand to determine the impact on the measured values of damage of the mechanical subsystem on which the MFC-type piezoelectric transducer was glued. Results of measurements are presented and analysed in relation to different applications of the piezoelectric MFC sensors.

Active aerothermoelastic flutter suppression of composite laminated panels with time-dependent boundaries

Aerothermoelastic characteristics of composite laminated panels with time-dependent boundary conditions are investigated. The macro fiber composite (MFC) which is more adaptive and effective than the traditional monolithic piezoelectric materials is applied to control the structural vibration. The MFC actuator and sensor are bonded on the top and bottom surfaces of the panel so that the active flutter control can be conducted. Aerodynamic pressure is evaluated by the supersonic piston theory. The governing equation of the electromechanical and thermal coupling system is established by the extended Hamilton’s principle with the assumed modes method. By solving the eigenvalue problem, natural frequencies of the structural system are obtained. Frequency- and time-domain responses are computed to analyze the aerothermoelastic properties of the laminated panel. The influences of ply angle and aspect ratio of the laminated panel on the flutter behaviors are investigated. The displacement feedback control (DFC) and linear quadratic Gaussion (LQG) methods are performed to design the controllers. The active control effects under the two different controllers are compared. It is observed that both the DFC and LQG methods can suppress the vibration, and the LQG is more effective than the DFC controller in flutter suppression of the laminated panel with time-dependent boundary conditions.

Load monitoring using a calibrated piezo diaphragm based impedance strain sensor and wireless sensor network in real time

The last decade has seen the use of various wired–wireless and contact–contactless sensors in several structural health monitoring (SHM) techniques. Most SHM sensors that are predominantly used for strain measurements may be ineffective for damage detection and vice versa, indicating the uniapplicability of these sensors. However, piezoelectric (PE)-based macro fiber composite (MFC) and lead zirconium titanate (PZT) sensors have been on the rise in SHM, vibration and damping control, etc, due to their superior actuation and sensing abilities. These PE sensors have created much interest for their multi-applicability in various technologies such as electromechanical impedance (EMI)-based SHM. This research employs piezo diaphragms, a cheaper alternative to several expensive types of PZT/MFC sensors for the EMI technique. These piezo diaphragms were validated last year for their applicability in damage detection using the frequency domain. Here we further validate their applicability in strain monitoring using the real time domain. Hence, these piezo diaphragms can now be classified as PE sensors and used with PZT and MFC sensors in the EMI technique for monitoring damage and loading. However, no single technique or single type of sensor will be sufficient for large SHM, thus requiring the necessary deployment of more than one technique with different types of sensors such as a piezoresistive strain gauge based wireless sensor network for strain measurements to complement the EMI technique. Furthermore, we present a novel procedure of converting a regular PE sensor in the ‘frequency domain’ to ‘real time domain’ for strain applications.

A New Fault Location Approach for Acoustic Emission Techniques in Wind Turbines

The renewable energy industry is undergoing continuous improvement and development worldwide, wind energy being one of the most relevant renewable energies. This industry requires high levels of reliability, availability, maintainability and safety (RAMS) for wind turbines. The blades are critical components in wind turbines. The objective of this research work is focused on the fault detection and diagnosis (FDD) of the wind turbine blades. The FDD approach is composed of a robust condition monitoring system (CMS) and a novel signal processing method. CMS collects and analyses the data from different non-destructive tests based on acoustic emission. The acoustic emission signals are collected applying macro-fiber composite (MFC) sensors to detect and locate cracks on the surface of the blades. Three MFC sensors are set in a section of a wind turbine blade. The acoustic emission signals are generated by breaking a pencil lead in the blade surface. This method is used to simulate the acoustic emission due to a breakdown of the composite fibers. The breakdown generates a set of mechanical waves that are collected by the MFC sensors. A graphical method is employed to obtain a system of non-linear equations that will be used for locating the emission source. This work demonstrates that a fiber breakage in the wind turbine blade can be detected and located by using only three low cost sensors. It allows the detection of potential failures at an early stages, and it can also reduce corrective maintenance tasks and downtimes and increase the RAMS of the wind turbine.

Active Vibration Control for a Large Annular Flexible Structure via a Macro-Fiber Composite Strain Sensor and Voice Coil Actuator

Large annular flexible structures (LAFS) are typical antenna structures for satellites. This structure can significantly increase antenna aperture and effectively improve communication accuracy with minimum addition of mass. LAFS have become mainstream for large aperture antenna structures. However, they have disadvantages, such as low natural frequencies, low damping ratio, and low stiffness. They easily suffer from low frequency, longtime and modal responses. Therefore, the vibration control of LAFS is very important. This study proposes a novel active vibration control method using macro-fiber composite (MFC) as a sensing unit, a voice coil actuator and a PD-fuzzy control algorithm. The MFC sensor can measure a minimum strain of 10-8 m/m. The voice coil actuator generates a displacement and driving force. Based on the feedback signal from the MFC sensor, the PD-fuzzy control algorithm controls the voice coil actuator. A dynamic model of LAFS was established, and its characteristics analyzed. A theoretical model for the voice coil actuator and MFC sensor were established, and the corresponding governing equations derived. An experimental system was set up. The results demonstrated that the novel active vibration control method has good performance. This active vibration control method can control vibration at ultralow frequencies and requires no additional stiffness.

Damage detection using the signal entropy of an ultrasonic sensor network

Piezoelectric ultrasonic sensors used to propagate guided waves can potentially be implemented to inspect large areas in engineering structures. However, the inherent dispersion and noise of guided acoustic signals, multiple echoes in the structure, as well as a lack of an approximate or exact model, limit their use as a continuous structural health monitoring system. In this work, the implementation of a network of piezoelectric sensors randomly placed on a plate-like structure to detect and locate artificial damage is studied. A network of macro fiber composite (MFC) sensors working in a pitch–catch configuration was set on an aluminum thin plate 1.9 mm in thickness. Signals were analyzed in the time-scale domain using the discrete wavelet transform. The objectives of this work were threefold, namely to first develop a damage index based on the entropy distribution using short time wavelet entropy of the ultrasonic waves generated by a sensor network, second to determine the performance of an array of spare MFC sensors to detect artificial damage, and third to implement a time-of-arrival (TOA) algorithm on the gathered signals for damage location of an artificial circular discontinuity. Our preliminary test results show that the proposed methodology provides sufficient information for damage detection, which, once combined with the TOA algorithm, allows localization of the damage.

Structural Health Monitoring in Cylindrical Structures Using Helical Guided Wave Propagation

Defect detection and characterization are critical tasks for structural health monitoring of pipe-like engineering structures. Propagation and detection of ultrasonic helical Lamb waves using macro fiber composite (MFC) sensors is studied. Experiments for defect detection and characterization on an aluminum hollow cylinder (114mm in outer-diameter and 6mm of wall thickness) were carried out. An experimental setup using MFC sensors coupled to the cylinder's surface in a pitch-catch configuration is presented. Time-frequency representation (TFR) using wavelets is employed to accurately perform mode identification of the ultrasonic captured signals. The initial results indicate that the use of helical waves could allow the monitoring of damage in difficult to access critical areas by locating the sensors only on a small region of the periphery of the cylindrical structure under inspection.

Damage location by ultrasonic Lamb waves and piezoelectric rosettes

An approach based on macro-fiber composite transducer rosettes and ultrasonic guided waves is proposed for damage location in plate-like structures. By using the directivity behaviour of the three macro-fiber composite sensors in each rosette, the direction of an incoming wave generated by scattering from damage can be estimated without knowledge of the wave velocity in the structure. Two rosettes suffice to identify the location of a scatterer in a planar structure. The technique does not have the drawbacks of time-of-flight triangulation, requiring information on wave velocity that complicates the damage location when testing anisotropic materials, tapered sections or any structure under temperature fluctuations. The effectiveness of the piezoelectric rosette method is tested experimentally on an aluminium plate with a simulated damage subjected to temperature variation.

Scattering Matrix Approach to Informing Damage Monitoring and Prognosis in Composite Bolted Connections

Structural health monitoring refers to the process of making an assessment, based on nondestructive, in-situ, autonomous measurements, about the ability of a structure to perform its intended function. This paper presents work done on a bolted connection in carbon-fiber reinforced polymer composite materials. A composite specimen is bolted in a double lap joint configuration to a test apparatus that applies an increasing tensile load. Ultimately, the load results in bearing failure of the material around the bolt hole. To monitor the progression of damage, macro fiber composite sensors are bonded in a circular array around the bolt hole. These sensors are then used to generate ultrasonic guided waves, a popular technique in nondestructive evaluation because of the favorable combination of propagation distance and sensitivity to damage. As the specimen is subjected to increasing load levels, measurements are taken repeatedly and compared with one another. Because damage will change the local mechanical properties of the material, the ultrasonic waves passing through the damaged region will be scattered differently in each direction, resulting in a different waveform arriving at the other surrounding sensors. By applying appropriate signal processing techniques, these changes may be interpreted as indicating the extent of damage that has occurred in the specimen. Preliminary analysis is presented demonstrating the correlation between changes in received strain signals and increasing damage levels.

An Investigation on Dynamic Signals of MFC and PVDF Sensors: Experimental Work

In the present paper, identification of dynamic sensing characteristics of macrofiber composite (MFC) and polyvinylidene fluoride (PVDF) is carried out via experimental investigation. As a first step, basic characteristics and operating principles of MFC and PVDF are briefly reviewed. Then, a clamped aluminum beam structure is prepared and experimental setup for vibration signal test is established with shaker system. Both MFC and PVDF are attached on the top and bottom surface of the beam structure, respectively, and connected to data acquisition system. In order to verify the operating bandwidth, frequency responses of the smart beam structure are obtained from 0 Hz to 5 kHz under sine sweep excitation. For the identification of dynamic sensing characteristics, experiments for linearity, durability, and robustness are conducted. It is observed that both MFC and PVDF have excellent sensing performance in measuring dynamic response and monitoring structural vibration.

Comparison of Dynamic Signal of MFC and PVDF Sensor: Experimental Investigation

In this paper, identification of dynamic sensing characteristics of MFC(macro fiber composite) and PVDF(polyvinylidene fluoride) are carried out via experimental investigation. A clamped aluminum beam structure is prepared and experimental setup for beam vibration test is established with shaker system. MFC and PVDF are attached on the top and bottom surface of the beam structure, respectively and connected to data acquisition system. In order to verify the operating bandwidth, frequency responses of the smart beam structure are obtained from 0Hz to 5kHz under sine sweep excitation. For the identification of dynamic sensing characteristics, experiments for linearity and durability are conducted. It is observed that both MFC and PVDF have excellent sensing performance in measuring dynamic response and monitoring structural vibration.

High-velocity Impact Location on Aircraft Panels Using Macro-fiber Composite Piezoelectric Rosettes

In this article, an approach based on an array of macro-fiber composite (MFC) transducers arranged as rosettes is proposed for high-velocity impact location on isotropic and composite aircraft panels. Each rosette, using the directivity behavior of three MFC sensors, provides the direction of an incoming wave generated by the impact source as a principal strain angle. A minimum of two rosettes is sufficient to determine the impact location by intersecting the wave directions. The piezoelectric rosette approach is easier to implement than the well-known time-of-flight-based triangulation of acoustic emissions because it does not require knowledge of the wave speed in the material. Hence, the technique does not have the drawbacks of time-of-flight triangulation associated to anisotropic materials or tapered sections. The experiments reported herein show the applicability of the technique to high-velocity impacts created with a gas-gun firing spherical ice projectiles.

Vibration analysis and optimal control of rotating pre-twisted thin-walled beams using MFC actuators and sensors

Structural modeling of rotating pre-twisted thin-walled composite beams with embedded macro fiber composite (MFC) actuators and sensors using higher shear deformation theory (HSDT) is presented in the present work. The governing system of equations is derived from Hamilton's principle and solution is obtained by extended Galerkin's method. Optimal control problem is solved using linear quadratic Gaussian (LQG) control algorithm. Vibration characteristics and optimal control for a box beam configuration are discussed in the numerical examples. It is observed in the present study that, gyroscopic coupling between lagging-extension motions is found to have significant effect and cannot be neglected in the analysis. Effects of vibration suppression using MFC actuators and sensors are highlighted.

2608 膜状圧電センサを用いた配管の腐食損傷評価(S22-2 非破壊評価とモニタリング(2),S22 非破壊評価とモニタリング)

The purpose of this research is to develop an advanced monitoring method which can measure damage progression of pipes utilizing both the guided wave and acoustic emission. The authors utilized a flexible Macro Fiber Composite (MFC) sensor. The MFC is made from small piezoelectric fibers and can be wound on the pipe surface. The MFC sensor was found to detect AEs from the fracture of rust produced by wet corrosion. Next the author evaluated depth of shallow defects (wall reduction less than 4.5%) utilizing the guided wave which was excited and monitored by the MFC sensors. We are now successful in detecting the L-mode wave reflected by the dish-shaped defects with average wall reduction less than 1.1%.