This article provides a thorough introduction to smart materials, encompassing their definition and various types. It discusses several examples of smart materials like piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, and shape memory alloys. Additionally, it emphasizes the wide range of smart material options available and ongoing research aimed at creating new ones. The article also extensively covers the applications of these different types of smart materials.
Smart materials are the focus of study in various applications, with future expectations and predictions presented later. The paper concludes that smart materials will become a prominent trend in multiple engineering fields.
INTRODUCTION: Smart material refers to a type of material that can predictably or controllably alter its mechanical properties (such as shape, stiffness, and viscosity) or its thermal, optical, or electromagnetic properties in response to environmental factors.
The economic well-being of a country depends on the creation of durable and cost-effective high-performance construction materials and systems, as civil infrastructure expenses are a significant factor in national wealth. To address the challenges presented by decaying civil infrastructure, research on smart materials is essential. This paper focuses on utilizing smart materials to guarantee optimal performance and safe design for buildings and other infrastructures, particularly in earthquake-prone areas and regions susceptible to other natural hazards.
The unique characteristics of shape memory alloys make them an exciting field of study for smart structures. Smart materials can be divided into two main categories: sensing materials, which offer information on their current state or ‘health’ (such as optical fibers, piezoelectric material, and electrostrictive material), and actuating materials, which alter their dimensions when exposed to external stimuli (such as heating/cooling or the presence of an electromagnetic field). Actuating materials generate a force when constrained.
Examples of special materials include shape memory alloy, piezoelectric material, and magnetostrictive material. These materials have unique properties such as shape memory, generation of electricity under mechanical stress, and deformation under the influence of a magnetic field. Another category of materials is self-repairing materials, which have the ability to automatically heal cracks. Examples of self-repairing materials include cementitious material and polymeric material. It should be noted that some materials can exhibit multiple properties mentioned above, and it is advantageous to use them in combination with conventional materials. One example of sensing materials is optical fibers, which have been developed with crack monitoring capability by Wolff and Messelier (1992), Ansari et al (1993), Voss and Wanser (1994).
It is also utilized for moisture content detection. Michie et al (1994) created a sensor for moisture detection.
2. Piezoelectric materials possess two interconnected distinctive properties. When deformed, these materials produce a small but measurable electrical material and also undergo a significant increase in size (up to 4% change in volume). They are commonly used in measuring fluid compositions, fluid density, fluid viscosity, or impact force.
PVDF materials have been found to offer an enhanced electrical response in stress and pressure sensing.
Actuating Materials
1. Piezoelectric materials: Piezoceramic materials can function as strain sensors by utilizing the direct piezoelectric effect, which converts mechanical action into an electric charge. Additionally, these materials can be utilized for actuation purposes by employing the converse piezoelectric effect, which converts an electrical field into a mechanical strain.
2. Shape memory alloys: Shape memory alloys (SMA’s) are metallic substances that possess two distinct properties, namely pseudo-elasticity and the shape memory effect. Examples of such alloys include Ni – Ti and Cu – Al – Zn, among others.
The properties of self-repairing materials that make them suitable for civil engineering applications include: 1. The ability to absorb large amounts of strain energy while under load without causing permanent deformation. This behavior can be adjusted by varying the number and/or characteristics of shape memory alloy (SMA) components, allowing for a wide range of cyclic behavior from supplemental and fully reentering to highly dissipating. 2. These materials have a usable strain range of 70%. 3. They exhibit exceptional fatigue resistance even when subjected to large strain cycles. 4. They also offer excellent durability and reliability over the long term.
Compared to smart sensors and actuators, self-repair materials are still in the early stages of development. The University of Illinois has conducted studies demonstrating the feasibility of self-repair in both cementitious and polymeric materials. In order for a material to possess self-repair capability, it must have internal storage for the repair material (typically a polymer or monomer), a stimulus for releasing the chemical, and a method for hardening the chemical or drying out water if a monomer is used. Smart materials offer several advantages. 1.
Piezoelectric ceramics, such as PZT, exhibit a significant piezoelectric response. Shape memory alloys have the main advantage of biocompatibility. The first notable industrial application of shape memory alloys was seen in 1969 with the development of a cryogenic Pipe fitting device by Raychem Corporation. Self-repair materials offer the major advantage of eliminating the need for regular inspection or monitoring, as they can repair themselves when damaged.
However, there are disadvantages associated with smart materials. Shape memory alloys are still relatively expensive to manufacture compared to materials like steel and aluminum. Additionally, most shape memory alloys have poor fatigue properties, meaning they are less durable under the same loading conditions as steel components.
Furthermore, fiber optic sensors have limitations, including the high cost of signal demodulation systems. Moreover, smart materials face restrictions related to non-linearity, hysteresis, creep, depoling, electrical breakdown, and Curie temperature.
One application of smart materials is their use as a substitute for steel.
According to reports, CuZnAl-SMA’s fatigue behavior is similar to steel, indicating potential use in civil engineering applications if larger diameter rods can be manufactured. Another promising material for smart structures is carbon fiber reinforced concrete, which can conduct electricity and change conductivity with mechanical stress. This material has evolved as part of DRC technology, enabling the production of surfaces stronger and more durable than metals and plastics. By adding just 0.5% specially treated carbon fibers, the electrical conductivity of concrete can be increased, making it suitable for both structural purposes and sensing. While the development of true smart materials at the atomic scale is still a ways off, the necessary technologies are being developed, including nanotechnology and shape chemistry.
The development of smart materials and structures is globally pursued for diverse applications, such as space, aerospace, civil engineering, and domestic products. Yet, the cost benefits of these systems are still under investigation. The concept of creating materials and structures that adjust to their environment, including the individuals utilizing them, remains relatively unfamiliar.
When evaluating these materials and structures, it is crucial to consider the technological and financial implications, as well as public understanding and acceptance. To summarize, more research and development is necessary to establish smart materials as dependable, long-lasting, and cost-efficient choices for large-scale civil engineering projects. Smart material technologies offer advantages for both new constructions and existing ones. It is undeniable that in the future, the utilization of smart materials will become a prominent trend across various engineering disciplines.
