MSMAs are magnetic metallic compounds undergoing a martensitic transformation and reaching a self-accommodated variant structure. Our expertise in tailored design of functional materials at the macro- and nano-scale, including fabrication processes,characterization structural behaviour, advanced physical properties, mechanisms of functions and theoretical studies will position BCM as a world-leading centre in science and engineering of MSMAs and related magneto-structural materials.
These changes can be used to developa large variety of smart devices. Smart polymers are easy to processand integrate in advanced functional devices eg. Skip to main content. Instead of having to make a machine that opens or closes a little door, for example, you simply use a smart material that swells and shrinks when appropriately stimulated.
I'll show an example of this later. So I think one of the key concepts behind smart materials is that of the 'invisible machine': a device that has no cogs, gears and levers, but instead grows, extends or shapes itself to do the task at hand. You'll notice that this sounds a lot like a living organism, and indeed a lot of the inspiration for developing smart materials comes from looking at biological materials and structures, which are able to grow, to adapt, to repair, to harvest energy and to communicate with one another in various ways.
I shall end by touching on this idea of so-called biomimetic materials science. The concept of smart materials may be new, but smart materials themselves go back a long way.
I mentioned piezoelectrics, which produce an electrical signal when squeezed. Some natural minerals are piezoelectric, such as quartz. A vibrating quartz crystal in old radio sets used to generate and receive the radio signal. The Curie brothers discovered the piezoelectricity of minerals like this in In the late s a robust piezoelectric ceramic material called barium titanate was discovered, and it became used as a sensor of mechanical vibrations in sonar devices.
One of the most common and important piezoelectrics in use today is a closely related material called lead zirconate titanate, which is abbreviated to PZT.
Piezoelectric materials like this can be used to make sensors for pressure and strain: both very important for engineering applications like bridges and buildings, where you want to know how much load the structure is carrying and how much it is deforming as a result. Some polymers are also piezoelectric, such as polyvinylidene fluoride - this is very convenient, because whereas ceramics are hard and brittle, polymers are tough and flexible.
Thin sheets of polymers like this are used in touch-sensitive keyboards, for instance. Here we're turning pressure into an electrical signal. Piezoelectric materials can do the reverse too: if you apply a voltage across them, they contract or expand, turning electrical energy into mechanical. This can be used to make piezoelectric drivers for inducing motion. They're used, for instance, in dot-matrix printers. A similar property called electrostriction, where a material contracts in an electric field, is used to make 'smart mirrors' for astronomy, which can change shape.
The idea here is that the mirror constantly adapts its shape to compensate for the distortions of starlight caused by turbulence in the atmosphere. Adaptive optics is now widely used in astronomy to improve the sharpness of the images from ground-based telescopes.
By driving vibrations in piezoelectric materials using an electrical signal, it's possible to make composite materials with a variable and tunable stiffness. This can be used for vibration damping - you can tune the material's properties so as to absorb the vibrations and avoid resonances.
Toyota have developed a suspension system for their Lexus range of cars that uses this kind of controlled-stiffness structure. Another well-established smart material is photosensitive glass, which darkens in response to sunlight. The process is similar to the way that photographic films darken, but is reversible. The glass contains dispersed silver halide crystals doped with copper. The copper ions give up an electron to the silver ions when irradiated by sunlight, converting them to neutral silver atoms which then aggregate into tiny silver particles that scatter light.
When the light is shut off, the silver atoms lose an electron back to the copper. It seems to me that this is an ideal illustration of what smart materials do-which is to say, the smart response is dramatic and yet so unobtrusive that we quickly learn to take it for granted.
It is now possible to make glass that can be switched between transparent and opaque electrically, which can be used to make smart windows that can be opened or closed without any moving parts. Now, you've all got a piece of this [Nitinol wire]. Here's what it does.
I did, and I knew what to expect. I think that is very telling: we don't expect ordinary-looking substances to do this kind of thing. It feels almost as though you have something living in your hand.
That's a very visceral illustration of what is different about smart materials: they are counter-intuitive, acting almost as though they have intelligence and purpose.
This is a piece of an alloy called Nitinol, sometimes known colloquially as memory metal. You can see why: it seems to remember that it is supposed to be straight. In general, it can be 'programmed' to remember any shape. Heat triggers the memory, making it return to its original shape after it's been deformed. Nitinol is an alloy of nickel and titanium, and was developed by the US Navy in the s.
It's an example of a so-called shape memory alloy. This stuff has become more familiar just recently, when it was introduced for the frames of spectacles [image]. These look like ordinary glasses, but the frames are made from a titanium shape-memory alloy called Titanflex.
If they get bent, you can restore the original shape just by warming them up. That's preferable to bending the bent frame back into shape by hand, which ends up weakening the metal. I'm waiting for someone to start making Nitinol tent pegs, but until then there is already a range of applications.
Shape-memory alloys can be used to make temperature-controlled switching mechanisms. Just think what you'd normally need: a temperature sensor coupled to some mechanical motor-like device.
The shape-memory alloy subsumes all of that in a single material, which is its own temperature sensor and mechanism in one. Nitinol wires are used as artificial muscles in some robotic devices, and as dental braces and implants that can remember their shape.
How does it work? The key is that the metal has a different atomic-scale structure at low and high temperature. When its structure changes, the movement of atoms induces a macroscopic change in shape or volume. It's possible to set things up so that, when the metal is heated through this structural change, any deformations it has accumulated get ironed out. Well, we don't have metals yet like the one used for the new range of Terminator robots, but perhaps the closest we can get is a substance that can be switched between a solid and a liquid by an electrical field.
These are called electrorheological fluids. Their viscosity is electrically controllable, which makes them useful as shock absorbers and vibration dampers. They can also be used in a contact-free clutch: two plates immersed in an electrorheological fluid can spin freely, but when the fluid is rigidified they become locked together. The fluids are suspensions of microscopic particles, which become strongly polarized in an electric field.
This creates an attraction between oppositely polarized ends of different spheres, inducing them to aggregate into long chain-like structures [image]. Silica particles in water show this behaviour, but better electrorheological fluids are now made from polymer microspheres suspended in silicone oils, which remain active at higher temperatures. This is important since many applications, such as shock absorption, dissipate energy and heat up the fluid.
The principle is the same: the fluid is a suspension of tiny magnetic particles which stick together in chains in an applied magnetic field. Here the spikes in the fluid are formed along field lines from magnets below the droplet. MR fluids are used in exercise cycles to control the resistance to the turning of the pedals. It's a smart valve for controlling fluid flow in a so-called microfluidic system. The idea here is that liquids are guided down microscopic channels carved into a material like a silicon wafer by gates, valves and pumps.
Microfluidic systems are being developed for conducting analytical chemistry on very small samples, by building effectively an entire chemical laboratory on a silicon chip. Instead of all those glass tubes and flasks, the whole thing is miniaturized so that you can work with a single tiny drop of material: mixing it with other reagents and analysing the results. The lab on a chip should be useful in medicine, for instance, or forensic science, or environmental monitoring: you can do all this analysis in situ, because the lab fits easily into your pocket.
For example, they change their shape in response to an electrical impulse or produce an electrical charge in response to an applied mechanical stress. They have the ability to change the shape, even returning to their original shape, when exposed to a heat source, among other stimuli. They change colour when subjected to a certain variation in temperature, light, pressure, etc.
Nowadays, they are used in sectors such as optics, among others. They change their properties when exposed to a magnetic field. For example, they are currently used in shock absorbers to prevent seismic vibrations in bridges or skyscrapers.
There are several types: electroluminescents emit light when they are fed with electrical impulses, fluorescents reflect light with greater intensity and phosphorescents are able to emit light after the initial source has ceased. Materials science is a constant supply of news about new discoveries that could revolutionise our future. We review some of the most amazing materials from recent years below:.
The main properties of graphene. In addition, there are other materials that have made headlines in recent years. These include stanene, which could be the super condenser of the future; silicone, which many compare to graphene; vanadium dioxide, with an ability to transit electricity without emitting heat, which promises to revolutionise electronics; and thermochromic cement and self-repairing concrete, intended to increase the energy efficiency of housing and the life span of buildings respectively.
One of the areas of research where materials science has advanced most in recent years is in the development of new materials for use in 3D printing, which is already used in sectors as diverse as design, medicine, architecture and food. The most widely used are thermoplastics, especially polylactic acid PLA and acrylonitrile butadiene styrene ABS , which are used in mobile phone casings, toys and car bodies.
Smart materials are also starting to be printed thanks to 4D printers. Skip to main content. You are in Innovation Smart materials.
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