Knowledge of integrity of in-service structures can greatly enhance their safety and reliability and lower structural maintenance cost. Current practices limit the extent of real-time knowledge that can be obtained from structures during inspection, are labor-intensive and thereby increase life-cycle costs. Utilization of distributed sensors integrated with the structure is a viable and cost-effective means of monitoring the structure and reducing inspection costs. Acellent Technologies is developing a novel system for actively and passively interrogating the health of a structure through an integrated network of sensors and actuators. Acellent's system comprises of SMART Layers™, SMART Suitcase™ and diagnostic software. The patented SMART Layer™ is a thin dielectric film with an embedded network of distributed piezoelectric actuators/sensors that can be surface-mounted on metallic structures or embedded inside composite structures. The SMART Suitcase™ is a portable diagnostic unit designed with multiple sensor/actuator channels to interface with the SMART Layer™, generate diagnostic signals from actuators and record measurements from the embedded sensors. With appropriate diagnostic software, Acellent's system can be used for monitoring structural condition and for detecting damage while the structures are in service. This paper enumerates on the SMART Layer™ and SMART Suitcase™ and their applicability to composite and metal structures.
In this paper, a detailed description for the ETDR distributed strain sensing mechanism of a coaxial cable was presented, and a signal calibration algorithm for interpreting ETDR signal waveforms was developed. In addition, a prototype coaxial ETDR distributed strain sensor with improved signal sensitivity was presented. The ETDR signal responses of the prototype sensor subjected to a concentrated lateral compression load and distributed axial tension load were experimentally tested. The test results showed that the prototype sensor has a substantially improved signal sensitivity over a commercial RG-174 cable of comparable size. It was also shown that the relation between the impedance change of the sensor and the applied axial tensile strain depends primarily on the mechanical stress–strain response of the sensor. From the test results, it was demonstrated that this relation could be empirically established with the aid of the calibration algorithm.
This article summarizes the latest development efforts on the Stanford multiactuator‐receiver transduction (SMART) Layer technology used for structural health monitoring (SHM) for various applications. The SMART Layer consists of a network of thin piezoelectric sensors and actuators that are embedded into a dielectric film through an electronic circuit printing and lamination technique. The SMART Layer provides a viable and cost‐effective means for monitoring the health of structures of various configurations and sizes. The SMART Layer is very versatile, and by coupling it with appropriate diagnostic software and hardware, the same layer can be developed into a passive SHM system or an active SHM system. The passive and active systems are specifically designed for detection of impacts on a structure; diagnosis of cracks in metallic structures and impact damage and debonds in composite structures. Recent advances in techniques for fabricating the SMART Layers, as well as methods for integrating the layers into structures, are illustrated and examples are presented. The mechanical and electrical properties of the layer are highlighted, including the effect of embedment of the layer on the integrity of composite structures. Other practical issues, such as the environmental effect on the performance of the layer and the self‐diagnostics of the embedded network, are also discussed.
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