Smart and Intelligent Materials

A

REPORT

ON

SMART AND INTELLIGENT MATERIALS

SUBMITTED BY:

KESHAV GUPTA

TABLE OF CONTENT

1)Introduction …………………………………………………………….…

2)Requirement of smart and intelligent materials……………………………

3)Smart and intelligent materials……………………………………………

4)Smart structures…………………………………………………………..

5)Classification of smart materials……………………………………….....

5.1) Piezoelectric………………………………………………………….

5.2) Magnetostrictive……………………………………………………..

5.3) Shape memory alloys………………………………………......

5.4) Self healing materials……………………………………………….

5.5) Fibre optics………………………………………………………….

5.6) Electro rheological and Magneto rheological Fluids…………….....

6) Applications……………………………………………………………..

7) Conclusion……………………………………………………………….

1)INTRODUCTION

Each of us reacts to the world around and within us by sensing and actuating. When our hand is in contact with a hot object, we sense the heat, our brain sends a command, and our arm muscles actuate our hand away from the object. Similarly, because of internal sensing, we will tend to favour the burned hand until it has healed. As technology progresses, it becomes reasonable to ask, “Can we design analogous mechanisms that can intelligently interact with their environment, and structures that assess their own health?” Such smart structures could have a tremendous impact in advancing many fields including medicine, microelectronics, and robotics, among others.

Often, simple devices made from a single sensing or actuating material are used in certain applications. However, systems that involve both sensing and actuating materials can be used to build more sophisticated applications. Such systems are referred to as smart structures, which incorporate sensors and actuators with processing/control units connecting them. To get an idea of how smart structures can be implemented, it is necessary to understand the fundamental components of these structures: sensor and actuator materials. Sensors are materials that respond to a physical stimulus, such as a changein temperature, pressure, or illumination, and transmit a resulting signalfor monitoring or operating a control. Actuators are materials that respondto a stimulus in the form of a mechanical property change such as a dimensionalor a viscosity change.

2)REQUIREMENT OF SMART AND INTELLIGENT MATERIALS

Today the drive to innovation is stronger than ever. Novel technologies and applications are spreading in all fields of science. Consequently, expectations and needs for engineering applications have increased tremendously,and the prospects of smart technologies to achieve them are very promising. Following figure summarizes these inter-relationships.

To achieve a specific objective for a particular function or application, a new material or alloy has to satisfy specific qualifications related to the following properties:

1) Technical properties, including mechanical characteristics such as plastic flow, fatigue and yield strength; and behavioural characteristics such as damage tolerance and electrical, heat and fire resistance.

2) Technological properties, encompassing manufacturing,forming, welding abilities, thermal processing,waste level, workability, automation and repair capacities.

3) Economic criteria, related to raw material and production costs, supply expenses and availability.

4) Environmental characteristics, including features such as toxicity and pollution.

3) SMART AND INTELLIGENT MATERIALS

Smart or intelligent materials are materials that have the intrinsic and extrinsic capabilities, first, to respond to stimuli and environmental changes and, second, to activate their functions according to these changes. The stimuli could originate internally or externally.

Since its beginnings, materials science has undergone a distinct evolution: from the use of inert structural materials to materials built for a particular function, to active or adaptive materials, and finally to smart materials with more acute recognition, discrimination and reaction capabilities.

Components of a smart material (or system) include some type of sensor (that detects an input signal), and an actuator (that performs a responsive and adaptive function). Sensors are materials that respond to a physical stimulus, such as a change in temperature, pressure, or illumination, and transmit a resulting signal for monitoring or operating a control. Actuators are materials that respond to a stimulus in the form of a mechanical property change such as a dimensional or a viscosity change. Actuators may be called upon to change shape, position, natural frequency, or mechanical characteristics in response to changes in temperature, electric fields, and/or magnetic fields.

Fig: Basic components of smart materials

4)SMART STRUCTURE

A smart structure is a system that incorporates particular functions of sensing and actuation to perform smart actions in an ingenious way. The basic five components of a smart structure are summarized as follows-

a) Data Acquisition (tactile sensing):The aim of this component is to collect the required raw data needed for an appropriate sensing and monitoring of the structure.

b) Data Transmission (sensory nerves):The purpose of this part is to forward the raw data to the localand/or central command and control units.

c) Command and Control Unit (brain):The role of thisunit is to manage and control the whole system by analyzing the data, reaching the appropriate conclusion,and determining the actions required.

d) Data Instructions (motor nerves):The function of thispart is to transmit the decisions and the associatedinstructions back to the members of the structure.

e) Action Devices (muscles):The purpose of this part isto take action by triggering the controlling devices/ units.

5) Classification of Smart Materials

5.1) Piezoelectric

5.2) Magnetostrictive

5.3) Shape memory alloys

5.4) Self healing materials

5.5) Fibre optics

5.6) Electro rheological and Magneto rheological Fluids

5.1) Piezoelectric:

Piezoelectric is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical strain. The word piezoelectricity means electricity resulting from pressure. Piezoelectricity is the direct result of the piezoelectric effect. The piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry. The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (the internal generation of electrical charge resulting from an applied mechanical force) also

exhibit the reverse piezoelectric effect (the internal generation of a mechanical force resulting from an applied electrical field). For example, lead zirconate titanate crystals will generate measurable piezoelectricity when their static structure is deformed by about 0.1% of the original dimension. Conversely, those same crystals will change about 0.1% of their static dimension when an external electric field is applied to the material.

Piezoelectricity is found in useful applications such as the production and detection of sound, generation of high voltages, electronic frequency generation, microbalances, and ultrafine focusing of optical assemblies. It is also the basis of a number of scientific instrumental techniques with atomic resolution, the scanning probe microscopes such as STM, AFM, MTA, SNOM, etc., and everyday uses such as acting as the ignition source for cigarette lighters and push-start propane barbecues.

5.2) Magnetostrictive

Magnetostrictive is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of material's magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ. The effect was first identified in 1842 by James Joule when observing a sample of nickel. (Compare with electrostriction)This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.

Magnetic materials have internal areas called domains, within which all magnetic dipoles are oriented in the same direction. Domains with different orientations are separated by domain walls or boundaries. With the application of an external magnetic field, the boundaries move and domains rotate and align themselves in the same direction, ultimately causing a slight length/shapechange in the bulk material.

The magnetostrictive effect is illustrated in the figure.

Fig : MACROSCOPIC MAGNETOSTRICTION MECHANISM

Although usually minimal, ferromagnetic materials (e.g. Fe, Ni, Co, etc.) exhibit magnetostrictive to some extent. Ferromagnetic elements, such as cobalt, are often alloyed with iron. Rare earth elements have exhibited significantly higher magnetostrictive but only at temperatures lower than room temperature. Other common magnetostrictive materials include nickel-based alloys and particulate composites containing magnetostrictive particles. Magnetostrictive sensors and actuators are used for transducers, transformers, MEMS, vibration and noise control, linear motors, adaptive optics, ultrasonic, speakers, drills, pumps, and position and mechanical torque sensors.

5.3) Shape memory alloys

Shape memory alloys (SMAs) are actuators that, upon proper thermal and mechanical treatment, have the ability to remember up to two shapes which they had previously occupied. When subjected to a mechanical load below a certain temperature, these special materials can be plastically deformed beyond their elastic limit, but then are capable of regaining their original shape if they are then heated above a certain temperature. Nickel-titanium is the most common SMA and has some of the best shape memory properties, but has relatively low transformation temperatures.

Although they cannot match the outstanding shape memory capabilities of Ni-Ti alloys, copper-based alloys are a less expensive alternative. The most common ternary Cu-based systems are Cu-Zn-Al and Cu-Al-Ni which can generally achieve a shape memory strain of 4 to 5% (compared to about 8% for Ni-Ti) and have a broader range of transformation temperatures. Other alloys, such as iron-based alloys ( e.g. Fe-Mn, Fe-Mn-Si, Fe-Pt, Fe-Ni, Fe-Ni-Co and Fe-Pd), exhibit shape memory but are not capable of regaining their shape to the same extent as nickel-titanium and copper-based alloys. Other forms of SMAs include composites and ferromagnetic alloys. Some of the current SMA applications include use in spacecraft, aircraft, automobiles, electronics, medicine, process systems, robotics, and domestic appliances.

5.4) Self healing materials

Self-healing materials are a class of smart materials that have the structurally incorporated ability to repair damage caused by mechanical usage over time. The inspiration comes from biological systems, which have the ability to heal after being wounded. Initiation of cracks and other types of damage on a microscopic level has been shown to change thermal, electrical, and acoustical properties, and eventually lead to whole scale failure of the material. Usually, cracks are mended by hand, which is difficult because cracks are often hard to detect. A material (polymers, ceramics, etc.) that can intrinsically correct damage caused by normal usage could lower production costs of a number of different industrial processes through longer part lifetime, reduction of inefficiency over time caused by degradation, as well as prevent costs incurred by material failure. For a material to be defined as self-healing, it is necessary that the healing process occurs without human intervention.

5.5) Fibre optics

An optical fiber is a thin, flexible, transparent fiber that acts as a waveguide, or "light pipe", to transmit light between the two ends of the fibre. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

Optical fiber typically consists of a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those that only support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,050meters (3,440ft).

5.6) Electro rheological and Magneto rheological Fluids

Electro rheological (ER) and magneto rheological (MR) fluids experience a nearly instantaneous change in their rheological properties upon the application of an electric or magnetic field, respectively. This change is reversible and occurs also nearly instantaneously upon the removal of the applied field. The physical changes can be quite substantial, turning a low viscosity fluid into a much more viscous, almost-solid substance.

The electro rheological effect occurs in an ER fluid when an electric field is applied causing the uniformly dispersed solid particles to become polarized. Once polarized, they begin to interact with each other, and form chain-like structures, parallel to the electric field direction, connecting the two electrodes (see figure below). Upon further intensification of the electric field, the chains begin to form thicker columns.

A dramatic change in the suspension’s rheological properties is associated with this change in its structure. The columnar particle structures give the fluid a greater yield stress. Upon removing the electric field, the particles lose their polarization and return to their freely roaming state. The period of time over which these events occur is on the order of milliseconds. The magneto rheological effect is similar to the ER effect, but obviously, instead of an electric field, a magnetic field is applied to polarize the particles.

Fig: THE ELECTRO- AND MAGNETO-RHEOLOGICAL EFFECTS

ER and MR fluids are mostly considered for use in damping applications. Specific applications include exercise equipment, valve, braking and clutch systems, as well as in vibration control and shock absorbing systems.

6) APPLICATIONS

a)Vibration reduction in sporting goods: A new generation of tennis rackets, golf clubs, baseball bats and ski boards have been introduced to reduce the vibration in these sporting goods, increasing the user’s comfort and reducing injuries.

b) Noise reduction in vehicles: Filaments of piezoelectric ceramic fibre shaped into various geometries are used in conventional fabric or materials processing to counter noise in vehicles, neutralize shaking in helicopter rotor blades, or nullify or at least diminish vibrations in air conditioner fans and automobile dashboards.

c) Smart Skin:In battle soldiers could wear a T-shirt made of special tactile material that can detect a variety of signals from the human body, such as detection of hits by bullets. It can then signal the nature of the wound or injury, analyze their extent, decide on the urgency to react, and even takes some action to stabilize the injury.

d) Smart Aircraft: few potential locations for the use of smart materials and structures in aircraft are central control unit, cabin noise reduction, engine monitoring, vibration damping impact detection etc.

e) Stealth Applications: The smart vehicles could be constructed using stealth technologies for their own protection: the B-2 stealth bomber or the F-117 stealth fighters are good examples of this technology. And, just as important, smart systems are needed for rapid and reliable identification of space or underwater stealth targets. The identification and detection of such targets, as well as the subsequent decision to take action with or without operator intervention, is another potential application of smart systems.

f) Autonomous Smart systems: Ground, marine or space smart vehicles will be a feature of future battles.These carriage systems, whether manned or unmanned, and equipped with sensors, actuators and sophisticated controls, will improve surveillance and target identification and improve battlefield awareness.

7) CONCLUSION

Today, the most promising technologies for lifetime efficiency and improved reliability include the use of smart materials and structures. Understanding and controlling the composition and microstructure of any new materials are the ultimate objectives of research in this field, and is crucial to the production of good smart materials. The insights gained by gathering data on the behaviour of a material’s crystal inner structure as it heats and cools, deforms and changes, will speed the development of new materials for use in different applications. Structural ceramics, superconducting wires and Nano structural materials are good examples of the complex materials that will fashion nanotechnology. New or advanced materials to reduce weight, eliminate sound, reflect more light, dampen vibration and handle more heat will lead to smart structures and systems which will definitively enhance our quality of life.

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