Strain properties analysis and wireless collection system of PVDF for structural local health monitoring of civil engineering structures

For large civil engineering structures and base establishments, for example, bridges, super-high buildings, long-span space structures, offshore platforms and pipe systems of water & gas supply, their lives are up to a few decades or centuries. Damaged by environmental loads, fatigue effects, corrosion effects and material aging, these structures experience inevitably such side effects as damage accumulation, resistance reduction and even accidents. The traditional civil structure is a kind of passive one, whose performance and status are unpredictable to a great extent, but the informatics' introduction breaks a new path to obtain the status of the structure, thus it is an important research direction to evaluate and improve reliability of civil structures by the use of monitoring and health diagnosis technique, and this also assures the security of service for civil engineering structures. Smart material structure, originated from the aerospace sector, has been a research hotspot in civil engineering, medicine, shipping, and so on. For structural health monitoring of civil engineering, the research about high-performance sensing unit of smart material structure is very important, and this will possibly push further the development and application of monitoring and health diagnosis techniques. At present, piezoelectric materials are one of the most widely used sensing materials among the research of smart material structures. As one of the piezoelectric materials, PVDF(Polyvinylidene Fluoride)film is widely considered for the advantages of low cost, good mechanical ability, high sensibility, the ability of being easily placed and resistance of corrosion. However, only a few studies exit about building a mature monitoring system using PVDF. In this paper, for the sake of using PVDF for sensing unit for structural local monitoring of civil engineering, the strain sensing properties of PVDF are studied in detail. Firstly, the operating mechanism of PVDF is analyzed. Secondly, wireless collection system of PVDF is integrated with PVDF film, charge amplifier, wireless transceiver and the corresponding software. Then, with strain gauge as a reference, experiments have also been done to study the quasi-static and dynamic strain response of PVDF, such as sensitivity, linearity and frequency responding, etc. The experimental results show that PVDF is sensitive to the impact response of civil engineering structures, and can provide local monitoring in different frequency response cooperating with a strain gauge. The developed wireless collection system has the characteristics of no lines, saving cost and installation time, and thus further pushes the practical application of PVDF for civil engineering structures.