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The geometric properties of cylindrical structures are complex as compared with plate-like structures. Structural health monitoring of such structures is thus more complicated. Even though many efforts have been carried out on the detection of cracks in cylindrical structures, the crack sizes and orientations have not received enough attention. Recently, a method to correlate the root-mean-square deviation change of torsional wave pack of signal with axial crack growth has been developed. In this article, based on the same principle and experimental setup, the detection of crack size and orientation is studied. Macro-fiber composite transducers are used as either an actuator or a sensor. First, a crack of finite size is induced in a laboratory specimen. Later, the size is gradually increased along various orientations. The effects of the crack size and transmitted waves, captured by the sensor, are correlated with the root-mean-square deviation values of the torsional wave packs and the longitudinal wave packs. The results show that both size and orientation of the crack can be evaluated based on the proposed method. The system developed in this article is easy to setup, cost-effective, and able to achieve automatic continuous online monitoring with good results. [ABSTRACT FROM PUBLISHER]

Energy harvesting from ambient vibrations using piezoelectric effect is a promising alternative solution for powering small electronics such as wireless sensors. A conventional piezoelectric energy harvester usually consists of a cantilevered beam with a proof mass at its free end. For such a device, the second resonance of the piezoelectric energy harvester is usually ignored because of its high frequency as well as low response level compared to the first resonance. Hence, only the first mode has been frequently exploited for energy harvesting in the reported literature. In this article, a novel compact piezoelectric energy harvester using two vibration modes has been developed. The harvester comprises one main cantilever beam and an inner secondary cantilever beam, each of which is bonded with piezoelectric transducers. By varying the proof masses, the first two resonant frequencies of the harvester can be tuned close enough to achieve useful wide bandwidth. Meanwhile, this compact design efficiently utilizes the cantilever beam by generating significant power output from both the main and secondary beams. An experiment and simulation were carried out to validate the design concept. The results show that the proposed novel piezoelectric energy harvester is more adaptive and functional in practical vibrational circumstances. [ABSTRACT FROM AUTHOR]

In the last few decades, piezoceramic (PZT) transducers have been extensively used either as actuators or as sensors in the vibration and noise control of aero, civil, and mechanical (ACM) systems. Only in the last decade, PZT transducers have been used in the electromechanical impedance (EMI) models as both sensor and actuator for the structural health monitoring of ACM systems. In the EMI models, the PZT transducers are generally surface bonded to the host structure and are then subjected to one-dimensional (1D) voltage to interrogate the structure for the desired frequency range. The interrogation results in the prediction of electromechanical admittance signatures. These signatures serve as indicators of the health/integrity of the structure. However, the existing single PZT–structure interaction models consider the PZT transducer to be negligible in mass and thus ignored. Moreover, they impose restrictions on the PZT shape, size, and isotropy. This paper presents a novel semianalytical multiple three-dimensional PZT–structure interaction model which considers the “mass” of the PZT transducers, and the transducers are subjected to parallel (1D) sinusoidal voltage. Further, the model does not impose restriction on the shape (square or rectangular), size (thin or thick), and electrical properties (isotropic or anisotropic) of PZT. The derived model is also experimentally verified using lab-sized aluminum plate. As it is generic, the model is expected to be applicable for the nondestructive evaluation of most ACM systems. [ABSTRACT FROM AUTHOR]

A damage model for concrete is proposed based on the existing displacement equivalence-based model for brittle materials. The model is established in a randomly selected coordinate system so as to consider the cases where the principal directions of damage do not coincide with those of stress and strain. The effect of shear stress is also considered. The slipping cracks of concrete under triaxial compression and the stiffness reduction under hydrostatic compression are also taken into account. The friction at crack tips has been introduced to account for the permanent deformation and a blend of elastic and secant unloading/reloading routine is obtained. The evolution rule of damage is combined with the predefined basic damage evolution patterns. [ABSTRACT FROM AUTHOR]

A three-dimensional damage model for concrete has been proposed in the preceding paper, Part I: Theory. This paper focuses on the application of the damage model for quasi-brittle materials such as concrete. The determination of model parameters for the evolution rule of damage is discussed. The model parameters to consider the frictional stress and the stiffness reduction under hydrostatic compression are also studied. For verification, the proposed model is applied to concrete subjected to confined compression, triaxial, loading, and cyclic loading. Consistent results, as compared with other researchers’ experimental data, were obtained, and the proposed model is considered worthy of further research work. [ABSTRACT FROM AUTHOR]

Piezoceramic transducers (PZTs) are extensively used in the nondestructive evaluation of damages in various engineering structures. This paper, the second of a two-part paper, focuses on the application of a PZT using three-dimensional (3D) directional sum impedance (DSI). The semianalytical 3D admittance has been formulated and experimentally validated in the first paper. This part deals with the application of the 3D DSI model in damage analysis where by damages were numerically simulated for various types of specimens and the DSI admittance signatures were predicted and compared. The deviations of the signature from that of the undamaged state provide an indicator for the health of the structure. This technique is nondestructive in nature, and the damages were quantified using root-mean-square deviation in signatures with respect to the undamaged state signature. In Part I, the properties of the PZT and their influences on admittance signatures were briefly presented. In this part, a thorough investigation was made and the importance of all the PZT properties in damage analysis was presented. [ABSTRACT FROM AUTHOR]