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Application of intelligent materials in civil engineering.

With the increasing demand for the quality and function of civil engineering, various intelligent materials, including optical fiber, piezomagnetism, piezoelectric and memory alloy, have been widely used in the field of civil engineering. This paper introduces the concept, characteristics and application of intelligent materials in civil engineering, and looks forward to its future application trend.

Intelligent materials; Civil engineering; Characteristics; development trends

introduce

At present, with the development of materials such as optical brazing, piezomagnetism, piezoelectricity and shape memory alloy, smart materials have been widely used in various fields of civil engineering. The most basic intelligent materials are generally called sensing materials, which can sense the substances excited by internal and external stimuli. Materials that can adapt to the environment by sensing changes in internal and external conditions are called driving materials. Nowadays, intelligent materials generally need a variety of materials to assemble, and realize the diagnosis, repair and adjustment of material structure under environmental changes.

I. Types and characteristics of smart materials

The concept of intelligent materials was put forward systematically in the early 1980s, and gained unprecedented development space in the late 1980s. With the development of intelligent materials such as optical fiber, piezomagnetism and shape memory alloy, they have been widely used in civil engineering. Intelligent materials can usually be divided into two categories because of their different functional characteristics. One kind is a material that can perceive the intensity of external or internal stimuli, which is called perceptual material. The other kind is materials that can respond or drive changes due to external environmental conditions or internal conditions, also known as intelligent driving materials. Smart material structure has three elements: control, sensing and driving. It can use its own perception to process information, issue instructions and perform actions, and then realize various functions of self-monitoring, diagnosis, detection, repair, correction and adaptation of the structure. Generally speaking, it is difficult for a single functional material to have the above functions, and it can only be realized by compounding or assembling a variety of materials to form new intelligent materials.

Second, the application of intelligent materials in civil engineering

Application of 1. Shape Memory Alloy

Shape memory alloy is a kind of smart alloy material with shape memory effect. As a new functional material, the most important advantage is that the material can produce recovery stress higher than 700 MPa and recovery strain about 8% in the process of stimulating the shape memory effect of the material, and it also has strong energy transmission and storage capacity. The application of this characteristic can put materials into various structures to realize the application research of self-diagnosis, toughening, reinforcement and adaptive control of structures, and can also develop materials into intelligent actuators to carry out application research on structural deformation, damage, cracks and vibration. Pseudoelasticity and hysteresis of phase transformation are another advantage of shape memory alloys, and their stress-strain curves are annular during loading and unloading, indicating that materials can absorb and dissipate more energy during this process. Shape memory alloy has a phase transition recovery of up to 400 MPa. Combined with this feature, a passive energy dissipation control system of shape memory alloy can be developed to realize the pseudo-elastic performance of phase change, which can be used for energy dissipation and seismic passive control of civil engineering structures. Usually, the passive energy dissipation control system of shape memory alloy is installed between floors or at the bottom of the structure, and the deformation between floors of the structure is sensed through the energy dissipation system, so as to consume seismic energy. The relevant research results show that after the shape memory alloy structure is installed in the energy dissipator, the energy dissipator can absorb about two-thirds of the seismic energy and significantly restrain the displacement of the structure.

2. Application of piezoelectric materials

Piezoelectric materials generally refer to crystal materials with voltage at both ends after receiving pressure. The application of piezoelectric materials in civil engineering mainly includes static deformation control, noise control, earthquake resistance and wind resistance of structures. The traditional use method of piezoelectric materials is to sense the vibration of the structure through piezoelectric sensing elements, and realize the sensing and early warning of vibration by using the output results of sensors. On this basis, the appropriate control algorithm is used to control and quantify the input of piezoelectric body, so as to control the structural vibration, which is the research frontier of piezoelectric smart materials at present. With the development of research and technology, the application of piezoelectric intelligent structures in civil engineering should be more and more extensive.

3. The application of optical fiber

Optical fiber is a fibrous optical communication medium material, which consists of an outer cladding and an inner core. This material was originally used in communication transmission systems by using advanced information transmission technology. Photons, as information carriers, have higher speed and capacity than electrons, so they develop rapidly. Photons have high parallel processing ability and high information rate, and have given full play to their potential in information capacity and processing speed. Optical fiber materials have been used in monitoring, sensing and long-distance information transmission. Optical fiber is embedded in the traditional concrete structure as a sensing element to realize the functions of automatic monitoring, diagnosis, control, prediction and evaluation of various structural indexes, and driving elements such as shape memory alloy are embedded, and the information processing system and control elements are organically combined to make the concrete structure have intelligent functions, so as to realize the self-diagnosis and repair of the concrete structure. In the diagnosis of civil engineering structures and active control of earthquake response, optical fiber materials have always been an ideal material for designing sensors, and have been used in the detection and evaluation of the Three Gorges Dam in China.

4. Application of piezomagnetic materials

The application of piezomagnetic materials in civil engineering mainly includes magnetorheological materials and magnetostrictive materials. Based on the principle of magnetorheological materials, when the magnetic field strength is higher than the critical strength, magnetorheology changes from liquid to solid in a short time. Between solid and liquid, according to the characteristics of magnetorheological fluid, it has the characteristics of fast, controllable and reversible, and the energy needed to control the fluid characteristics is low. Therefore, magnetorheological fluid is usually used as the main material of power device in intelligent structure. Based on this, magnetorheological materials can be used in high-rise building structures to realize semi-active earthquake control. Magnetostrictive materials have attracted great attention in recent years because of their broad potential application prospects. Magnetostrictive materials have a strong magnetostrictive effect and can be reversibly converted between electromagnetic and mechanical. This characteristic makes it suitable for high-power ultrasonic devices, sonar systems, precise positioning control and many other fields.

Third, the development trend of intelligent materials

In the field of civil engineering, the development trend of intelligent materials focuses on the following three aspects. One is to monitor and detect the structural state in real time, integrate the sensing and driving components in the civil structure, and use its network to monitor the structural state in real time, thus ensuring the safety of the civil engineering structure and infrastructure and effectively reducing the maintenance cost. Secondly, shape adaptive materials and structures can not only carry and transmit motion, but also detect and change structural characteristics, which has broad application prospects. Thirdly, the adaptive control of structural vibration reduction, earthquake resistance, wind resistance and noise reduction has always been an important issue in civil engineering design, especially for the earthquake resistance and wind resistance of civil engineering structures such as bridges and high-rise buildings. The development and application of intelligent materials provide an important way to realize the adaptive control of structures. Although there are still some shortcomings in the current smart materials, with the deepening of related research, the performance of smart materials will be significantly improved. In many fields, smart materials will exert their potential and show broad application prospects. The research includes mechanics, computer control, materials, microelectronics, artificial intelligence and other disciplines and technologies.

Four. conclusion

To sum up, with the wide application of intelligent materials and the gradual development of miniaturized, multifunctional and high-power components, the building structure will develop into an active intelligent building structure integrating control, sensing, driving system and coupling/connecting components, which will play an important role in effectively utilizing solar energy, resisting the influence of serious natural disasters such as earthquakes and wind vibration, providing a more comfortable and safe environment for people's work and life, and improving the construction quality of civil engineering structures.

References:

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Zheng Zhi, Zhang Yongxing, Dong Qiang. Intelligent materials and their applications in civil engineering [J]. Journal of Chongqing Jiaotong University, 2005,24 (6): 91-94.

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