Smart Material Essay Example

indoors again. This coating is made from a type of smart material called photochromic. Smart materials are categorized into different groups, each having specific properties that can be utilized in various high-tech and everyday applications. One example of a smart material is shape memory, which can respond to its surroundings autonomously.

The inherent change in smart materials, triggered by temperature, stress, electrical current, or magnetic field, is independent of volume, color, or viscosity. This change can be reversed in examples like spectacles turning into sunglasses under UV light. Smart materials encompass alloys, piezoelectric materials, magneto-rheological and electro-rheological materials, magnetostrictive materials, and chromic materials that change color based on stimuli. It's important to differentiate between smart materials and smart structures as the latter involve actuators, sensors, control hardware and software to create a responsive system incorporating smart materials.

The aircraft wing undergoes continuous changes in its shape while in flight, enabling it to maintain an optimal profile for various operating conditions.

SHAPE MEMORY ALLOYS

Shape memory alloys (SMAs) have been widely used for 70 years since their discovery. They are well-known smart materials. The first observation of SMAs was in a gold-cadmium alloy in 1932 and later in brass in 1938. However, the shape memory effect (SME) gained significance when it was discovered in a gold-cadmium alloy again in 1951. Its usefulness was limited at that time. In 1962, Nitinol, an equiatomic alloy of titanium and nickel found at the Naval Ordinance Laboratories, exhibited a significant SME and became the most commonly used SMA due to its composition of nickel and titanium as well as exceptional properties compared to other SMAs such as copper-based (specifically CuZnAl), NiAl, and

FeMnSi alloys.

The working mechanism of Shape Memory Alloys (SMAs) entails a material undergoing a shape change or retaining a specific shape at a designated temperature, referred to as its transformation or memory temperature. SMAs are categorized as one-way or two-way based on their ability to demonstrate the shape change or memory effect only once or remember two shapes, respectively.

At the memory temperature, the alloy undergoes a solid state phase transformation known as a "thermoelastic martensitic transformation". This transformation causes a change in the crystal structure of the material, resulting in a change in volume or shape. Below the transformation temperature, the material has a martensitic microstructure characterized by a zig-zag arrangement of atoms called twins. The martensitic structure is soft and can be easily deformed by removing the twinned structure. Above the memory temperature, the material has an austenitic structure that is much stronger.

The material can switch from a martensitic or deformed structure to an austenitic shape by being heated to the memory temperature. Cooling it down again returns the alloy to the martensitic state, as shown in Figure 1. The shape change can result in either expansion or contraction. The transformation temperature can be adjusted by altering the alloy composition, allowing Nitinol to have a transformation temperature ranging from -100? C to +100? C, making it highly versatile. SMAs are widely utilized in aerospace, medicine, and the leisure industry.

A number of medical applications of Nitinol have been discovered due to its biocompatibility. It can be used in the body without any adverse reactions. Some of these applications include stents, blood filters, and bone plates. Stents use SMA wire rings to hold open a polymer

tube to clear blocked veins. Bone plates made from Nitinol contract upon transformation, bringing the two ends of a broken bone closer together to promote faster healing. SMAs may also have potential applications in orthodontic braces for teeth straightening.

The material's memory shape is designed to match the desired shape of the teeth, but it can be altered to conform to the actual shape of the teeth. Activation of the material's memory occurs when it comes into contact with the temperature of the mouth. As the material contracts, it applies enough force to gradually and slowly move the teeth. SMAs are also used in surgical tools, especially those used in key hole surgery. These tools can be bent to fit a specific patient's anatomy, but they return to their original shape after being sterilized in an autoclave. Although the use of SMAs as artificial muscles is still in the distant future.

The process of simulating the expansion and contraction of human muscles involves using SMA wire instead of a muscle on a robotic hand's finger. Heating the wire through an electrical current causes it to expand and straighten the joint, while cooling it causes the wire to contract, bending the finger again. However, achieving this in reality is extremely challenging due to the need for complex software and surrounding systems.

The shape memory effect is associated with a change in structure. NASA has been studying the use of SMA muscles in robots that can walk, fly, and swim. In domestic settings, SMAs can be used as actuators, exerting a force through shape change that can be repeated over many cycles. Examples include springs in greenhouse windows that open

and close at a specific temperature, and pan lids with an SMA spring in the steam vent.

When heated by boiling water, the spring in the pan changes shape, opening the vent to prevent the pan from boiling over and ensuring efficient cooking. These springs resemble those depicted in Figure 5. Shape Memory Alloys (SMAs) can be utilized to replace bimetallic strips in various household applications. SMAs have the benefit of providing a greater deflection and exerting a stronger force when there is a temperature variation.

They can be utilized in cut out switches for kettles and other devices, security door locks, fire protection devices like smoke alarms, and cooking safety indicators (for example, checking the temperature of a roast joint). Also, in aerospace applications, SMA wire is employed to control the flaps on the trailing edge of aircraft wings. Currently, hydraulic systems control the flaps, but these could be replaced by resistance-heated wires. Passing a current along them would induce the desired shape change. This system would be simpler than conventional hydraulics, reducing maintenance while decreasing weight. Additionally, in manufacturing applications, SMA tubes can serve as couplings for connecting two tubes.

The coupling diameter is slightly smaller than the tubes it connects, and is deformed to slip over the tube ends. The temperature changes to activate the memory, causing the coupling tube to shrink and hold the two ends together with a constant force. SMAs are highly flexible due to their shape memory effect and the structure of the martensite.

SMARTs have found various applications, including mobile phone aerials, spectacle frames, and underwire in bras. In surgical tools, the kink resistance of the wires is advantageous because they

maintain their straight shape when inserted into the body. Nitinol, unlike stainless steel, can be significantly bent without permanent deformation. Another unique application of SMAs is in intelligent fabrics where fine wires are woven into polyester cotton fabric. The super elastic material allows the wires to straighten out even when the fabric is crumpled, eliminating creases and resulting in a non-iron garment. Furthermore, the sleeves incorporate memory wires that activate at a specific temperature (e.g., 38°C), causing them to roll up and keep the wearer cool.

PIEZOELECTRIC MATERIALS

The piezoelectric effect, which was discovered in 1880 by Jaques and Pierre Curie during their experiments with quartz crystals, is the oldest form of smart material. Since then, ceramics have been extensively used as piezoelectric materials. This effect involves the relationship between voltage and shape change, which is opposite to electrostriction.

Like shape memory alloys (SMAs), the change in shape in piezoelectric materials is linked to a modification in their crystal structure. Piezoelectric materials also have two different types of crystalline structure. The first type is organized, which matches the polarization of the molecules. The second type is disorganized or unordered. When an electrical voltage is applied to the unordered material, it undergoes a transformation in shape as the molecules realign themselves to match the electric field.

Electrostriction is when a material's shape changes with an electrical field, while the piezoelectric effect is when an electrical field is generated by applying mechanical force to a material. These materials can quickly change shape or create an electrical field. So, what kinds of materials show this effect? The piezoelectric effect was first found in quartz and

other crystals like tourmaline.

Lead zirconium titanate (PZT), barium titanate, and cadmium sulphate are types of piezoelectric ceramics. PZT is the most frequently utilized ceramic because it can be modified through chemistry and processing methods. Nevertheless, PZT has drawbacks such as brittleness and challenges in integration with other components. These ceramics find primary application in actuators that transform electrical energy into mechanical motion. When a piezoelectric material is subjected to an electric field, its shape swiftly alters based on the field's intensity.

Various industries utilize applications that make use of the electrostrictive effect of piezoelectric materials. One such industry is semiconductor, where these materials are used as actuators for handling silicon wafers. In the field of microbiology, they play a role in systems for handling microscopic cells. They also have applications in fiber optics and acoustics, as well as ink-jet printers for precise movement control and vibration damping. Additionally, sensors that generate an electrical field when subjected to mechanical force rely on the piezoelectric effect. This is particularly useful in damping systems, earthquake detection systems in buildings, and notably, car airbag deployment systems. When impacted, the material changes shape and generates a field that triggers the release of the airbag.

The materials mentioned in this text have a unique application - they are used in smart skis that are designed for optimal performance in both soft and hard snow. These materials harness both the piezoelectric and electrostrictive effects. Piezoelectric sensors are used to detect vibrations, whereby the shape of the ceramic detector changes and creates a field. The electrostrictive property of the material is then utilized to counteract the vibration by generating an opposing shape change. The system

consists of three piezoelectric elements that can detect and eliminate significant vibrations in real-time due to the rapid reaction time of the ceramics. By applying an alternating voltage to these materials, a vibration is generated.

This process is highly efficient and converts almost all electrical energy into motion. It can be used for various purposes, such as creating silent alarms for pagers that can fit into a wristwatch. At low frequencies, the vibration remains silent, but at high frequencies, it produces an audible sound. This concept can also be applied to create solid-state speakers using piezoelectric materials that can be made smaller in size.

It is worth considering if polymers exhibit these effects too. Ionic polymers work similarly to piezoelectric ceramics but need moisture to function properly.

The piezoelectric effect is utilized in research for potential medical uses as it involves passing an electrical current through a wet polymer to change its crystal structure and shape. Muscle fibers, which operate similarly to polymers, have also been studied in this field. Magnetostrictive materials, on the other hand, involve a change in shape due to a magnetic field rather than an electrical field. These materials convert magnetic energy to mechanical energy and vice versa. The discovery of the magnetostrictive effect dates back to 1842 when James Joule noticed a length change in a nickel sample when it was magnetized.

Both cobalt and iron, along with their alloys, were discovered to exhibit the magnetostrictive effect. In the 1960s, terbium and dysprosium were also found to have this property, albeit only at low temperatures. Despite their limited usability, the size change observed in these elements was significantly greater than that of nickel. Today,

the most commonly used magnetostrictive material is TERFENOL-D, consisting of terbium (TER), iron (FE), Naval Ordanance Laboratory (NOL), and dysprosium (D). This alloy displays a substantial magnetostrictive effect and is employed in transducers and actuators.

The original observation of the magnetostrictive effect is known as the Joule effect, but there are other effects as well. The Villari effect is the opposite of the Joule effect - applying stress to the material causes a change in its magnetization. When a torsional force is applied to a magnetostrictive material, it generates a helical magnetic field, which is called the Matteuci effect. The Wiedemann effect, on the other hand, occurs when the material twists in the presence of a helical magnetic field. So how do magnetostrictive materials work? They contain domains that can be likened to tiny magnets within the material. When an external magnetic field is applied, these domains rotate to align with it, resulting in a shape change.

On the other hand, if an external force squashes or stretches the material, the domains will move, resulting in a change in magnetisation. Magnetostrictive materials have various uses, serving as actuators for shape change induced by a magnetic field and as sensors that convert movement into a magnetic field. In actuators, a magnetic field is typically produced by passing an electrical current through a wire. Similarly, the electrical current generated by the magnetic field caused by a shape change is often measured in sensors.

Early applications of magnetostrictive materials included telephone receivers, hydrophones, oscillators, and scanning sonar. The development of alloys with improved properties expanded the use of these materials into various applications. Examples of these applications are ultrasonic magnetostrictive transducers

in ultrasonic cleaners and surgical tools, as well as hearing aids, razorblade sharpeners, linear motors, damping systems, positioning equipment, and sonar.

MAGNETO AND ELECTRO RHEOLOGICAL MATERIALS

All the previously mentioned groups of smart materials have been primarily based on solids.

Smart fluids are fluids that can change their rheological properties based on their environment. These fluids can be divided into two types, which were both discovered in the 1940s. Electro-rheological (ER) materials undergo changes in their properties when an electrical field is applied. These materials are composed of an insulating oil, like mineral oil, which contains solid particles dispersed within it. In early experiments, substances like starch, stone, carbon, silica, gypsum, and lime were used as these solid particles.

On the other hand, magnetorheological materials (MR) are also based on a carrier fluid made of mineral or silicone oil. However, instead of solid particles, these fluids contain a magnetically soft material (such as iron) that is dispersed within them. By applying a magnetic field, the properties of the fluid can be altered.

Both smart fluids, ER fluids and MR fluids, have dispersed particles that are microns in size. The mechanism of action for smart fluids is the same in both cases - the fluid changes from a fluid to a solid when the relevant field is applied. This change is due to the alignment and attraction of the small particles in the fluid, leading to a significant increase in viscosity. This process happens rapidly, within milliseconds, and can be reversed by removing the field. Figure 7 illustrates this dramatic change in viscosity. Additionally, Figure 8 demonstrates the effect of a magnet on an MR fluid. ER fluids require

a field strength of up to 6kV/mm, while MR fluids only need a magnetic field strength of less than 1Tesla.

Smart fluids have various uses in civil engineering, robotics, and manufacturing. They can be found in electrodes, suspension fluids, and particles. In civil engineering, these materials are utilized for their ability to change viscosity when subjected to different field strengths, as depicted in Figure 7. When a higher field strength is applied, the particles align, causing the fluid's viscosity to change. Additionally, in the presence of a magnetic field, magnetorheological fluid can stiffen, as shown in Figure 8 (courtesy of Sandy Hill / University of Rochester). Researchers are currently investigating further applications for these unique materials.

The automotive and aerospace industries were the first to discover applications for smart materials like MR dampers. These industries use the fluids in vibration damping and variable torque transmission. In cars, MR dampers control the suspension to provide different ride experiences. Prosthetic limbs also use dampers to enable patients to adjust to different movements, such as transitioning from running to walking. The future holds endless possibilities for smart materials and structures.

The potential applications of smart materials in products and the range of smart structures that can be designed are only limited by one's creativity, skills, and ability to think innovatively. Early discussions and brainstorming sessions on future possibilities have paved the way for the exploration of numerous ideas. What once existed as conceptual notions are now being actively pursued. An example of progress can be seen in the use of smart materials and structures in automobiles, which provide enhanced information and comfort. For instance, when a car requires servicing, it can

be connected to a diagnostic computer at the garage, enabling the mechanic to identify the issues.

When a light on the dashboard signals 'maintenance required', it would be more helpful if it informed us about the specific nature and severity of the problem. This concept is illustrated by a cartoon from some years ago, where an air mechanic asks an airplane 'Where do you hurt?' One example of the use of smart materials is a piezoelectric inkjet printer, which can deliver chemicals to print organic light-emitting polymers in great detail on different media. We can apply this same approach to synthesize smaller molecules. With the appropriate tools, it would be possible to synthesize significant quantities of smaller molecules for characterization and evaluation, making it easier to design experiments.

A new category of smart materials called smart adhesives has emerged in recent literature. Within an adhesive joint, PVDF film strips have been incorporated to assess performance. At Lehigh University, Khongtong and Ferguson have created a smart adhesive.

0 This new adhesive has been suggested for use as an antifouling coating on boat hulls or for controlling cell adhesion during surgery. The adhesive's stickiness can be activated or deactivated by adjusting the temperature. Additionally, when the tackiness decreases, the smart adhesive becomes water repellent.

50 Recently, the term "smart adhesive" has been increasingly used in scientific literature. A few years ago, research on "smart clothes" or "wearable computers" was being conducted at MIT and discussed in the literature.

The potential of this concept is huge. It is amazing as long as we figure out how to work smarter, not longer.

CONCLUSION

The conclusion arises from the abilities of the smart material

to respond to environmental changes that the term "smart" in the name does not meet the definition of being smart, which is to respond to the environment in a reversible manner. Due to their properties, they are likely to have a great future.

REFERENCES

1. Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition. Edited by Myer Kutz.
2. www.memorymetals.co.uk
3. www.nitinol.

com

Here are some links to websites containing information about shape memory alloys: