This paper will provide an overview of the smart materials. The various types of smart material are also presented in this paper. To get the clear idea about the smart materials, its definition and types are explained briefly. Some of the types of these include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, and shape memory alloys piezoelectric, Varieties of smart materials already exist, and research is being carried out extensively to derive new materials. Applications of various types of smart materials are clearly explained.
Some of applications of already existing smart materials are studied. The expectations of the smart materials and the predictions of future applications have been presented on the later part of the paper. And it is concluded that the application of smart material in future becomes a trend in various fields in engineering. INTRODUCTION Smart material can be defined as material that can significantly change their mechanical properties (such as shape, stiffness, and viscosity), or their thermal, optical, or electromagnetic properties, in a predictable or controllable manner in response to their environment.
The development of durable and cost effective high performance construction materials and systems is important for the economic well being of a country mainly because the cost of civil infrastructure constitutes a major portion of the national wealth. To address the problems of deteriorating civil infrastructure, research is very essential on smart materials. This paper highlights the use of smart materials for the optimal performance and safe design of buildings and other infrastructures particularly those under the threat of earthquake and other natural hazards.
The peculiar properties of the shape memory alloys for smart structures render a promising area of research in this field. CLASSIFICATION OF SMART MATERIALS Smart materials can be broadly classified into the following categories: (i) Sensing materials – materials that can provide information on its current condition or ‘health’. Ex:optical fibers,piezoelectric material,electrostrictive material, (ii) Actuating materials – materials that can change dimensions under external stimulus (such as heating/cooling or the introduction of an electromagnetic field). When restrained, an actuating force will be provided.
Ex: shape memory alloy, piezoelectric material,magnetostrictive material. (iii) Self-repairing materials- materials that can repair themselves, for example, through the automatic healing of cracks. Ex: cementitious material,polymeric material. It should be noted that some materials exhibit more than one of the above properties and It is better to use them in combination with conventional material. Sensing Materials 1. Optical Fibers: Fiber optic sensors with crack monitoring capability have been developed by Wolff and Messelier (1992), Ansari et al (1993); Voss and Wanser (1994).
It is also used to detect moisture content. A sensor for moisture detection have been developed by Michie et al (1994). 2. Piezoelectric materials: Piezoelectric materials have two unique properties which are interrelated. When a piezoelectric material is deformed, it gives off a small but measurable electrical material it experiences a significant increase in size (up to a 4% change in volume). They are often used to measure fluid compositions, fluid density, fluid viscosity, or the force of an impact. In stress and pressure sensing, the PVDF materials have been found to give a better electrical response.
Actuating Materials 1. Piezoelectric materials: A piezoceramic material can be used as a strain sensor by taking advantage of the direct piezoelectric effect that converts a mechanical action into an electric charge. But the same material can be also used for actuation applications by using the converse piezoelectric effect that. converts an electrical field into a mechanical strain. 2. Shape memory alloys: Shape memory alloys (SMA’s) are metals, which exhibit two very unique properties, pseudo-elasticity, and the shape memory effect. eg. Ni – Ti, Cu – Al – Zn etc..
Its properties which enable them for civil engineering application are: 1. Repeated absorption of large amounts of strain energy under loading without permanent deformation. Possibility to obtain a wide range of cyclic behavior –from supplemental and fully reentering to highly dissipating-by simply varying the number and/or the characteristics of SMA components. 2. Usable strain range of 70%. 3. Extraordinary fatigue resistance under large strain cycles. 4. Their great durability and reliability in the long run. . Self Repairing Materials
Compared to smart sensors and actuators, self-repair materials are in a much earlier stage of development. The only reported studies, from the University of Illinois, have demonstrated the feasibility of self-repair in both cementitious and polymeric materials. For a material to possess self-repair capability, it is necessary to have. (i) a means for internal storage of the repair material (which is usually a polymer or a monomer) (ii) a stimulus to release the chemical; (iii) an approach to harden the chemical or dry out the water (if a monomer is used). ADVANTAGES OF SMART MATERIALS 1.
Piezoelectric ceramics, e. g. ,PZT, have a large piezoelectric response, Biocompatibility is one of the main advantage of shape memory alloys. 2. The first major industrial application of a shape-memory alloy was a cryogenic Pipe fitting device developed by Raychem Corporation in 1969. 3. The major advantage of self-repair material is to eliminate the need for regular inspection or monitoring, as the material can repair itself once damage occurs. DISADVANTAGES OF SMART MATERIALS 1. Shape memory alloys are still relatively expensive to manufacture as compared to other materials such as steel and aluminum. . . Most SMA’s have poor fatigue properties; this means that while under the same loading conditions (i. e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than SMA element. 3 the limitation related to fiber optic sensor is The cost of signal demodulation systems is still high. 4. The mostobvious limitations are associated with non-linearity, hysteresis, creep, depoling, electrical breakdown; Curie temperature. APPLICATIONS 1. Substitute for steel:
It is reported that the fatigue behavior of CuZnAl-SMA’s is comparable with steel. If larger diameter rods can be manufactured. It has a potential for use in civil engineering applications. 2. Carbon fiber reinforced concrete: Its ability to conduct electricity and most importantly, capacity to change its conductivity with mechanical stress makes a promising material for smart structures . It is evolved as a part of DRC technology (Densified Reinforced Composites).. This technology makes it possible to produce surfaces with strength and durability superior to metals and plastics. . Smart concrete: A mere addition of 0. 5% specially treated carbon fibers enables the increase of electrical conductivity of concrete. This concrete could serve both as a structural material as well as a sensor. THE FUTURE The development of true smart materials at the atomic scale is still some way off, although the enabling technologies are under development. These require novel aspects of nanotechnology (technologies associated with materials and processes at the nanometer scale, 10-9m and the newly developing science of shape chemistry.
Worldwide, considerable effort is being deployed to develop smart materials and structures. The technological benefits of such systems have begun to be identified and, demonstrators are under construction for a wide range of applications from space and aerospace, to civil engineering and domestic products. In many of these applications, the cost benefit analyses of such systems have yet to be fully demonstrated. The concept of engineering materials and structures which respond to their environment, including their human owners, is a somewhat alien concept.
It is therefore not only important that the technological and financial implications of these materials and structures are addressed, but also issues associated with public understanding and acceptance. CONCLUSION It is the field which is still in its infancy and further research and development is required to establish smart materials as reliable, durable and cost-effective materials for large-scale civil engineering applications. The technologies using smart materials are useful for both new and existing constructions. its sure that application of smart material in future becomes a trend in various fields in engineering.