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Composites

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4.7.1 Describe composites.

Composites are a combination of two or more materials that are bonded together to improve their mechanical, physical, chemical or electrical properties.

4.7.2 Define fibre.

A class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread with a length to thickness ratio of at least 80.
Fibre Composites

4.7.3 Describe the matrix composition of composites.

It is where one material acts as a glue 'matrix' holding the other material in place, such as Glass reinforced fibre (fibreglass). This is where the glass fibres are held by a plastic such as resin. The resin is the 'Glue'.

4.7.4 Explain that new materials can be designed by enhancing the properties of traditional materials to develop new properties in the composite material.

It is possible to enhance the properties of a material by adding another material with the properties that are wanted, an example would be improving the toughness of concrete by adding steel rods. concrete is hard (high compressive strength) and weak in tension but steel is tough and has high tension but not too hard, therefore by adding steel to concrete, we get a hard and tough composite material that is ideal for building. Something important to consider when making composites is thermal expansivity as two materials with different rates of expansion would break each other.

4.7.5 Describe a smart material.

Smart materials have one or more properties that can be dramatically altered, for example, viscosity, volume, conductivity. The property that can be altered influences the application of the smart material.

A smart fluid developed in labs at the Michigan Institute of Technology

Science and technology have made amazing developments in the design of electronics and machinery using standard materials, which do not have particularly special properties (i.e. steel, aluminium, gold). Imagine the range of possibilities, which exist for special materials that have properties scientists can manipulate. Some such materials have the ability to change shape or size simply by adding a little bit of heat, or to change from a liquid to a solid almost instantly when near a magnet; these materials are called smart materials.

  • An Article from Ash Tankha, US patent attorney.
  • A description of smart materials
Smart Materials Series from PBS Shape and property changing

4.7.6 Identify a range of smart materials.

Smart materials include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, shape memory alloys. Some everyday items are already incorporating smart materials (coffee pots, cars, the International Space Station, eye-glasses), and the number of applications for them is growing steadily.

4.7.7 Describe a piezoelectric material.

When a piezoelectric material is deformed, it gives off a small electrical discharge. When an electric current is passed through it, it increases in size (up to a 4% change in volume). They are widely used as sensors in different environments. Specific details of crystalline structure are not required.

The piezoelectric effect describes the relation between a mechanical stress and an electrical voltage in solids. It is reversible: an applied mechanical stress will generate a voltage and an applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume). In physics, the piezoelectric effect can be described as the link between electrostatics and mechanics. The piezoelectric effect occurs only in non-conductive materials. Piezoelectric materials can be divided in 2 main groups: crystals and ceramics. The most well known piezoelectric material is quartz (SiO2).

4.7.8 Outline one application of piezoelectric materials.

Piezoelectric materials can be used to measure the force of an impact, for example, in the airbag sensor on a car. The material senses the force of an impact on the car and sends an electric charge to activate the airbag.
(: Youtube ZEWCFjbqaaE:)
Airbag and Performance testing

Piezoelectric materials are also useful for guitar pickups, converting the vibrations on an acoustic guitar into an electric signal sent to an amplifier. Because they are only affected by vibration of the guitar, unwanted sounds do not affect the quality much. They can also be used for guitar tuners, also with the same advantage as piezoelectric pickups.

4.7.9 Describe electro-rheostatic and magneto-rheostatic materials.

Electro-rheostatic (ER) and magneto-rheostatic (MR) materials are fluids that can undergo dramatic changes in their viscosity. They can change from a thick fluid to a solid in a fraction of a second when exposed to a magnetic (for MR materials) or electric (for ER materials) field, and the effect is reversed when the field is removed.
The MR fluid is liquid as shown on the left,
when no magnetic field is present,
but turns solid immediately after being placed in a magnetic field on the right.

Electro-rheostatic (ER) and magneto-rheostatic (MR) materials are fluids, which can experience a dramatic change in their viscosity. These fluids can change from a thick fluid (similar to motor oil) to nearly a solid substance within the span of a millisecond when exposed to a magnetic or electric field; the effect can be completely reversed just as quickly when the field is removed. MR fluids experience a viscosity change when exposed to a magnetic field, while ER fluids experience similar changes in an electric field. (this is not referenced or in your own words)

The composition of each type of smart fluid varies widely. The most common form of MR fluid consists of tiny iron particles suspended in oil, while ER fluids can be as simple as chocolate milk or cornstarch and oil.

4.7.10 Outline one application of electrorheostatic materials and one application of magneto-rheostatic materials.

Safety features of Cars
Not Required to know but is cool
Prosthetic Limbs
MR fluids are being developed for use in car shock absorbers, damping washing machine vibration, prosthetic limbs, exercise equipment, and surface polishing of machine parts. ER fluids have mainly been developed for use in clutches and valves, as well as engine mounts designed to reduce noise and vibration in vehicles.

Excellent website from Lord not only advertising their products but showing many applications and how they work.

4.7.11 Describe shape memory alloys (SMAs).

SMAs are metals that exhibit pseudo-elasticity and shape memory effect due to rearrangement of the molecules in the material. Pseudo-elasticity occurs without a change in temperature. The load on the SMA causes molecular rearrangement, which reverses when the load is decreased and the material springs back to its original shape. The shape memory effect allows severe deformation of a material, which can then be returned to its original shape by heating it.
Smart Metals Thermal Expansion and
Shape Memory Alloy

NB Following is more depth than needed

After a sample of SMA has been deformed from its original crystallographic configuration, it regains its original geometry by itself during heating (one-way effect) or, at higher ambient temperatures, simply during unloading (pseudo-elasticity or superelasticity). These extraordinary properties are due to a temperature-dependent martensitic phase transformation from a low-symmetry to a highly symmetric crystallographic structure. Those crystal structures are known as martensite (at lower temperatures) and austenite (at higher temperatures). The three main types of SMA are the copper-zinc-aluminium-nickel, copper-aluminium-nickel, and nickel-titanium (NiTi) alloys. NiTi alloys are generally more expensive and possess superior mechanical properties when compared to copper-based SMAs.

4.7.12 Identify applications of SMAs.

Applications for pseudo-elasticity include eye-glasses frames, medical tools and antennas for mobile phones. One application of shape memory effect is for robotic limbs (hands, arms and legs). It is difficult to replicate even simple movements of the human body, for example, the gripping force required to handle different objects (eggs, pens, tools). SMAs are strong and compact and can be used to create smooth lifelike movements. Computer control of timing and size of an electric current running through the SMA can control the movement of an artificial joint. Other design challenges for artificial joints include development of computer software to control artificial muscle systems, being able to create large enough movements and replicating the speed and accuracy of human reflexes.

Shape memory alloys can be applied in many different products and situation: Nokia has recently developed a technology that utilises SMAs to make the process of recycling easier. Normally, when phones are reclaimed, it takes several minutes to take a phone apart to recycle its components. This tech would do it, hands-off, in two seconds, using heat. . The application of high heat (between 60-150C) causes the SMA to "actuate" and release the parts

Air flight turbulence control


References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on January 09, 2014, at 10:23 PM