| Structural health monitoring (SHM) is an emerging applied technology in recent years, dealing with the development of techniques and system for the continuous monitoring, inspection and damage detection of structures, and its ultimate goal is to increase reliability, improve safety and reduce maintenance costs. The technology can be applied to monitor structures during their whole life, such as critical parts of high-rating key equipments, bridges, dams, buildings, aeronautic and astronautic instruments, chemistry industrial containers, and electrical powers.The research of this dissertation is intended to meet the above engineering's needs, and develop a new kind of structural health monitoring technology based on sensing and actuating properties of shape memory alloys to provide a simple, economic and reliable technique method monitoring important engineering structures on line. Therefore, research on whether the shape memory alloy can be simultaneously used as sensor and actuator or not was conducted.Main research works can be summed up in four aspects.Firstly, the sensing and actuating characteristics of shape memory alloys were systematically studied and measured after analyzing shape memory effect and superelasticity. NiTi shape memory alloy wires and Cu-based helical springs were selected to test. The relationships among stress, strain, resistance and temperature of NiTi memory-wire and superelastic wire, which are in constant temperature, constant stress and shape recovery, were measured and analyzed. The actuating property of Cu-based spring in three basic conditions was investigated. Experimental results show that NiTi memory wire for pure martensite or pure austenite and superelastic wire has strain-sensing nature, and memory-wire and superelastic wire possess stress-actuating property during restrained recovery, and that NiTi superelastic wire can be used as strain-sensing element to monitor structural health condition.Secondly, structural impact response monitoring technology of composite materials based on NiTi superelastic nature was researched. Some typical experimental specimens embedded with superelastic wires were designed and fabricated. The dynamics of impact on fiber-reinforced composite structure was analyzed and summarized. Methods and reliability of structural health monitoring utilizing the large strain and electric property of shape memory alloy's superelasticity were studied by low velocity impact test. Theconclusion is that NiTi superelastic-sensing elements embedded in structure can be well used to monitor impact responses, such as impact position, impact degree, and so on.Thirdly, structural strength monitoring of composite materials embedded with NiTi superelastic sensing elements was researched. Experimental specimens embedded with superelastic wires, which are rectangle laminated composite panels with a circular hole and square plate, were prepared to make respectively tensile and bending test. The outputs of sensors embedded in structures were timely acquired to monitor mechanical properties of structure. Research results show that NiTi superelastic wires embedded in structures can monitor fracture behavior and strength in the structures.Fourthly, a dynamic property tester used to impact structure, which has multi-parameters testing function, and a health monitoring signal conditioner and amplifier were developed, and experimental system applied to monitor structural health was established. In order to realize low velocity impact test and measure parameters for composite structures embedded with NiTi sensing elements, low velocity impact tester was designed and manufactured by ourselves, which can be used to measure impact force, impact velocity, impact energy and so on. The multichannel signal conditioners and amplifiers were developed to monitor superelastic wires embedded in structure, and 16 channels parallel data acquisition and processing system was set up. So, the experimental system was established and successfully used as structural health monit...
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