Yourong Li

Proof-of-concept study of monitoring bolt connection status using a piezoelectric based active sensing method

Aimed at monitoring bolt connection status and detecting bolt loosening, a piezoceramic based active sensing method is developed in this article. Two piezoceramic patches are bonded to the two different parts of a bolted connection. In the active sensing approach, one piezoceramic patch is used as an actuator to generate an ultrasonic wave, and the other one is used to detect the wave that propagates through the bolted connection. The received energy depends on the interface fastening pressure which is determined by the bolt torque. By analyzing the received energy, the status of bolt connection and bolt loosening can be detected. To study the effectiveness of the proposed method, an experiment apparatus is set up, and the experimental results show that the wave energy propagated across the interface is proportional to the torque level that is used to pretension the bolt. This experimental study demonstrates the potential of the piezoceramic based active sensing method for the monitoring of bolt loosening status.

Review of Bolted Connection Monitoring

This paper reviews the research of monitoring technologies for bolted structural connections. The acoustoelastic effect based method, the piezoelectric active sensing method, and the piezoelectric impedance method are the three commonly used to monitor bolted connections. The basic principle and the applications of these three methods are discussed in detail in this paper. In addition, this paper presents a comparison of these methods and discusses their suitability for in situ or real-time bolt connection monitoring.

Dynamic cooperative identification based on synergetics for pipe structural health monitoring with piezoceramic transducers

The monitoring of structural integrity for pipes is one potential structural health monitoring (SHM) application using piezoelectric sensor networks. A dynamic cooperative identification method (DCIM) for pipe SHM with lead zirconate titanate (PZT) is proposed based on synergetics in this paper. A cooperative identification model with a cooperation–competition–update process was developed and its cooperative identification kinetic equation was established. With the governing principle, the order parameter equation and its potential function were acquired. On the basis of the synergetic effect principle, the adjoint vector was obtained from the regional vectors. By using the self-organization principle, the evolution of each order parameter was obtained through strict mathematical ratiocination. By implementing the iterative update principle, an online structural condition update feature was realized. Subsequently, the assessment indices were confirmed. Finally, the performance of the proposed methodology for damage identification for a pipe structural model with various connector damage scenarios created by loosening connectors was investigated. The experiments were conducted in a noisy environment, a disturbance rich environment, and a noisy and disturbance rich environment, separately. The results show that the proposed methodology can identify the healthy condition and various damage conditions within an acceptable monitoring range for metal pipes. Furthermore, the DCIM demonstrates a strong ability to reject disturbances and noise in SHM applications. This proposed approach provides an alternative way to carry out damage and fault identification for pipe engineering structures.

A multi-delay-and-sum imaging algorithm for damage detection using piezoceramic transducers

The traditional delay-and-sum imaging algorithm usually requires sending an excitation pulse at each piezoceramic transducer and obtains a damage image by drawing only ellipses. A multi-delay-and-sum imaging algorithm is proposed for damage detection of thin-plate-like structures using sparse piezoceramic transducers. Compared with the traditional delay-and-sum imaging algorithm, the proposed algorithm sends only one excitation pulse for each detection. A reflection coefficient is employed in the proposed method to cancel the artifacts caused by the boundary reflection signals, and the reflection coefficient is determined by the distribution of piezoceramic transducers and strength of the reflection signals. An additional time compensation due to the excitation pulse is also made to reduce the error of damage locating. To increase the image pixel value of a damage, the damage image is obtained by drawing both ellipses and hyperbolas with transmitter–sensor pair signals. The experimental results obtained on an aluminum alloy plate demonstrate that the proposed multi-delay-and-sum imaging algorithm can identify a bonded mass damage efficiently and accurately.

Characterization of Ultrasound Energy Diffusion Due to Small-Size Damage on an Aluminum Plate Using Piezoceramic Transducers

During the propagation of ultrasonic waves in structures, there is usually energy loss due to ultrasound energy diffusion and dissipation. The aim of this research is to characterize the ultrasound energy diffusion that occurs due to small-size damage on an aluminum plate using piezoceramic transducers, for the future purpose of developing a damage detection algorithm. The ultrasonic energy diffusion coefficient is related to the damage distributed in the medium. Meanwhile, the ultrasonic energy dissipation coefficient is related to the inhomogeneity of the medium. Both are usually employed to describe the characteristics of ultrasound energy diffusion. The existence of multimodes of Lamb waves in metallic plate structures results in the asynchronous energy transport of different modes. The mode of Lamb waves has a great influence on ultrasound energy diffusion as a result, and thus has to be chosen appropriately. In order to study the characteristics of ultrasound energy diffusion in metallic plate structures, an experimental setup of an aluminum plate with a through-hole, whose diameter varies from 0.6 mm to 1.2 mm, is used as the test specimen with the help of piezoceramic transducers. The experimental results of two categories of damages at different locations reveal that the existence of damage changes the energy transport between the actuator and the sensor. Also, when there is only one dominate mode of Lamb wave excited in the structure, the ultrasound energy diffusion coefficient decreases approximately linearly with the diameter of the simulated damage. Meanwhile, the ultrasonic energy dissipation coefficient increases approximately linearly with the diameter of the simulated damage. However, when two or more modes of Lamb waves are excited, due to the existence of different group velocities between the different modes, the energy transport of the different modes is asynchronous, and the ultrasonic energy diffusion is not strictly linear with the size of the damage. Therefore, it is recommended that only one dominant mode of Lamb wave should be excited during the characterization process, in order to ensure that the linear relationship between the damage size and the characteristic parameters is maintained. In addition, the findings from this paper demonstrate the potential of developing future damage detection algorithms using the linear relationships between damage size and the ultrasound energy diffusion coefficient or ultrasonic energy dissipation coefficient when a single dominant mode is excited.

A delay-and-Boolean-ADD imaging algorithm for damage detection with a small number of piezoceramic transducers

The delay-and-sum (DAS) imaging algorithm usually sends an excitation signal at each piezoceramic transducer and obtains a defect image by using transmitter–sensor pair signals to draw ellipses or hyperbolas. A delay-and-Boolean-ADD (DABA) imaging algorithm is developed for defect detection of plate-like structures with a small number of piezoceramic transducers. This new method requires sending only one excitation signal for each detection, and obtains a better defect image by employing Boolean ADD operation instead of addition or multiplication operation in the DAS algorithm. A reflection coefficient is introduced in the new algorithm to attenuate the signals reflected from the boundary. The widely used envelop-detection method based on Hilbert-transformation is replaced by a new envelop-detection technique based on a local maximum value to increase the accuracy of locating. An additional time shift due to the excitation signal itself is also considered to decrease the location error. The results of the experiments conducted on an aluminum plate indicate that the proposed DABA imaging algorithm combining with the new techniques can detect a bonded mass defect accurately and efficiently.

A piezoelectric active sensing method for detection of bolt load loss

Purpose – The purpose of this paper is to propose a bolt loosening detection approach which integrates piezoelectric ceramics with active sensor technology. Design/methodology/approach – When the ultrasonic wave propagates across the contact surface at the bolted joints, because of the existence of imperfect interface, only part of the ultrasonic wave energy is passed through it. According to the Hertz contact theory, the passed energy depends on the true contact area which is decided by the bolt pretension. Hence, by measuring the received energy with the sensing piezoelectric material, the bolt pretension or bolt loosening can be detected. Findings – The experiment revealed that the wave energy propagated across the interface is strongly correlated to the torque level. This relationship will be a good indicator to detect the status of bolted joints. The presented method has a potential application for the monitoring of bolt load loss in-site. Moreover, some factors which will affect the propagation of u...

Damage pattern recognition of refractory materials based on BP neural network

The determination of the damage mode and the quantitative description of the damage of the clustered acoustic emission (AE) signal of the refractory materials based on the BP (back propagation) Neural Network are the subjects of this paper. In this paper, a large number of AE signals in the process of a three-point bending test were studied and the pattern recognition system of refractory materials based on BP neural network was established with the AE characteristic parameters such as amplitude, counts, rise time, duration and centroid frequency etc. The results show that the total recognition rate of material damage types with this method is as high as 97.5%, and the prediction error of the extent of the damage is about 5%, which indicates that this method has the value of application and dissemination in the aspect of micro-damage pattern recognition and extent prediction of the damage.