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A2 Technology Product Design Systems and Control Notes DT4 - Exam
Material Technology 6
Materials Smart materials Composite materials Traditional materials
What are smart materials? Smart materials are materials that have one or more properties that can be significantly altered in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields.
What are the examples? Piezoelectric materials Shape memory alloys Magnetic shape memory alloys PH sensitive polymers Halochromic materials Chromogenic systems Others…
What are Piezoelectric materials? Piezoelectric materials are materials that produce a voltage when stress is applied. Since this effect also applies in the reverse manner, a voltage across the sample will produce stress within the sample. Suitably designed structures made from these materials can therefore be made that bend, expand or contract when a voltage is applied. Buzzers are piezoelectric.
What are shape memory alloys? Shape memory alloys and shape memory polymers are thermoresponsive materials where deformation can be induced and recovered through temperature changes.
What are shape memory alloys? An example is NiTinol TM (Nickel Titanium) Above its transformation temperature, Nitinol is superelastic, able to withstand a large amount of deformation when a load is applied and return to its original shape when the load is removed. Below its transformation temperature, it displays the shape memory effect. When it is deformed it will remain in that shape until heated above its transformation temperature, at which time it will return to its original shape.
Application of SMA Nitinol is used in medicine for stents: A collapsed stent can be inserted into a vein and heated (returning to its original expanded shape) helping to improve blood flow. Also, as a replacement for sutures where nitinol wire can be weaved through two structures then allowed to transform into it's pre-formed shape which should hold the structures in place.
Further reading of SMA
Magnetic SMA Magnetic Shape Memory alloys are materials that change their shape in response to a significant change in the magnetic field.
PH sensitive polymers pH-sensitive polymers are materials which swell/collapse when the pH of the surrounding media changes. The sensor is prepared by entrapping within a polymer matrix a pH sensitive dye that responds, through visible colour changes (see next slide) to spoilage volatile compounds that contribute to a quantity known as Total Volatile Basic Nitrogen (TVB-N).
PH sensitive polymers The ‘REF’ sample is outside the package. The others are all inside.
Halochromic Materials Halochromic materials are commonly materials that change their colour as a result of changing acidity. One suggested application is for paints that can change colour to indicate corrosion in the metal underneath them.
Chromogenic systems Chromogenic systems change colour in response to electrical, optical or thermal changes. These include electrochromic materials, which change their colour or opacity on the application of a voltage (e.g. liquid crystal displays), thermochromic materials change in colour depending on their temperature, and photochromic materials, which change colour in response to light - for example, light sensitive sunglasses that darken when exposed to bright sunlight.
Electrochromic Flip a switch and an electrochromic window can change from clear to fully darkened or any level of tint in-between. The action of an electric field signals the change in the window's optical and thermal properties. Once the field is reversed, the process is also reversed. The windows operate on a very low voltage -- one to three volts -- and only use energy to change their condition, not to maintain any particular state.
Thermochromic Kettles that change colour and signs that glow-in-the-dark are two recent examples of products becoming ‘smarter’ as a result of new materials. Colour-changing thermochromic pigments are now routinely made as inks for paper and fabrics – and incorporated into injection moulded plastics. A new type of phosphorescent pigment, capable of emitting light for up to 10 hours, has opened up entirely new design opportunities for instrumentation, low-level lighting systems etc. WarmCool
Photochromic Photochromism is the reversible transformation of colour upon exposure to light. This phenomenon is illustrated in sun glasses.
QTC Quantum Tunneling Composites (or QTCs) are composite materials of metals and non-conducting elastomeric binder, used as pressure sensors. As the name implies, they operate using quantum tunneling: without pressure, the conductive elements are too far apart to conduct electricity; when pressure is applied, they move closer and electrons can tunnel through the insulator. The effect is far more pronounced than would be expected from classical (non-quantum) effects alone, as classical electrical resistance is linear (proportional to distance), while quantum tunneling is exponential with decreasing distance, allowing the resistance to change by a factor of up to between pressured and unpressured states. QTCs were discovered in 1996 and PeraTech Ltd was established to investigate them further.
Not really that new!
Composite materials Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure.
Background The most primitive composite materials comprised straw and mud in the form of bricks for building construction; the Biblical book of Exodus speaks of the Israelites being oppressed by Pharaoh, by being forced to make bricks without straw being provided. The ancient brick-making process can still be seen on Egyptian tomb paintings in the Metropolitan Museum of Art. The most advanced examples perform routinely on spacecraft in demanding environments. The most visible applications pave our roadways in the form of either steel and aggregate reinforced portland cement or asphalt concrete. Those composites closest to our personal hygiene form our shower stalls and bath tubs made of fibreglass. Solid surface, imitation granite and cultured marble sinks and counter tops are widely used to enhance our living experiences.fibreglass
Materials There are two categories of constituent materials: Matrix (or binder) and reinforcement. –At least one portion of each type is required. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials allows the designer of the product or structure to choose an optimum combination. Engineered composite materials must be formed to shape. The matrix material can be introduced to the reinforcement before or after the reinforcement material is placed into the mold cavity or onto the mold surface. The matrix material experiences a melding event, after which the part shape is essentially set. Depending upon the nature of the matrix material, this melding event can occur in various ways such as chemical polymerization or solidification from the melted state.
Materials A variety of moulding methods can be used according to the end- item design requirements. The principal factors impacting the methodology are the natures of the chosen matrix and reinforcement materials. Another important factor is the gross quantity of material to be produced. Large quantities can be used to justify high capital expenditures for rapid and automated manufacturing technology. Small production quantities are accommodated with lower capital expenditures but higher labor and tooling costs at a correspondingly slower rate. Most commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, PEEK, and others.polyester vinyl esterepoxyphenolicpolyimidepolyamidepolypropylene PEEK
Materials The reinforcement materials are often fibres but also commonly ground minerals. The various methods described below have been developed to reduce the resin content of the final product, or the fibre content is increased. As a rule of thumb hand lay up results in a product containing 60% resin and 40% fibre, whereas vacuum infusion gives a final product with 40% resin and 60% fibre content. The strength of the product is greatly dependent on this ratio, so this increase in fibre content results in a dramatically stronger product.
Fibreglass Fibreglass also known as glass fibre) is material made from extremely fine fibres of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass- reinforced plastic (GRP), is called "fiberglass" in popular usage.
Fibreglass Glassmakers throughout history have experimented with glass fibers, but mass manufacture of fiberglass was only made possible with the advent of finer machine- tooling. In 1893, Edward Drummond Libbey exhibited a dress at the World's Columbian Exposition incorporating glass fibers with the diameter and texture of silk fibers. What is commonly known as "fiberglass" today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, ® which has become a generalised trademark.
Composites and Textiles Textile composites Textile composite materials consist of a polymer matrix (thermoplastic or thermoset) combined with a textile reinforcement. Materials of particular interest to the group include commingled glass/polypropylene fabrics, dry fabrics (woven, warp-knitted or braided) combined with thermoset resins via liquid moulding, and carbon/epoxy thermoset prepregs. Typical applications range from structural parts for high volume cars to high performance aerospace components.
Composites and Textiles Current activities are focused on prediction of processing and mechanical properties, process modelling and the interactions between manufacture and performance. Materials models are developed from a geometric description for a general textile structure. These are then implemented within models for draping/forming and subsequent performance. Process modelling for textile composites includes both formability (to eliminate wrinkles and tears) and impregnation (to eliminate dry patches or lengthy fill times). Using this approach, fabric iterations can be examined quickly and cheaply for a wide range of textile styles including knits, weaves, braids and hybrids tmlhttp://www.nottingham.ac.uk/unimat/expertise/textiles/composites.ph tml
Composite Materials Further reading … Kevlar Carbon Fibre
Injection Moulding Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called injection moulding. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes.
Injection Moulding Dies
Injection Moulding Advantages of Injection moulding The advantages of injection moulding are that a large number of components can be produced in a short time and all with a consistently good finish and quality. However when using with thermosetting plastics they can cure in the hopper or the screw, this causes a clog and halts production. Video
Extrusion Extrusion occurs one of two ways, either direct or indirect extrusion. In direct extrusion the material is fed through the die either using a ram or with a screw like the one used in the injection moulding. However the indirect extrusion works by forcing the die onto the material so that the material is forced through the die. Direct extrusion can be used to produce a continuous extrusion which can later be cut to the desired length. Only simple shapes can be produced and often the quality of the finish is quite poor.
Blow moulding High pressure air blown in to inflate form to shape of the mould
Rotational moulding Rotational moulding is very different from other plastics moulding techniques, and those differences generate its advantages. Rotational moulding is a unique, open- moulding, low-pressure, high- temperature process that uses biaxial rotation and heat to produce hollow one-piece plastic parts. Plastic footballs are made like this
Rotational moulding This process can be completed in school. Moulds or formers are made from a dense material, such as MDF. High Impact Polystyrene, is placed in the vacuum former and heated. Once the HIPs is soft the former is pressed into the plastic and the air is evacuated.
Cutting and Shaping WOOD(s) a
WOOD Is it a place to go for a walk or a collective name for a complex family of materials? Hardwood Softwood Manufactured Wood
Reactive Synthetic Glues Cyanoacrylate –“Super glue” is a brand of this type of glue Epoxy –“ARALDITE” is a brand of this type of glue Polyurethane –“TITEBOND” is a brand of this type of glue Urea Resin –“Cascemite” is a brand of this type of glue
Reactive Synthetic Glues Characteristics of reactive synthetic glues –Used to permamnently bond dissimilar materials together – Give a stronger, waterproof bond – Curing times vary
Reactive Synthetic Glues Contact adhesives “EVOSTICK” Contact adhesive is one which must be applied to both surfaces and allowed some time to dry before the two surfaces are pushed together. Some contact adhesives require as long as 24 hours to dry before the surfaces are to be held together. Once the surfaces are pushed together, the bond forms very quickly, hence, it is usually not necessary to apply pressure for a long time. This means that there is no need to use clamps, which is convenient. Natural rubber and Neoprene are commonly used contact adhesives. Both of these elastomers undergo strain crystallization. Contact adhesives find use in laminates, such as bonding Formica to a wooden counter, and in footwear, for example attachment of an outsole to an upper
PVA Polyvinyl acetate (PVA or PVAc) is a rubbery synthetic polymer. It is prepared by polymerization of vinyl acetate monomer, also referred to as VAM. Partial or complete hydrolysis of the polymer is used to prepare polyvinyl alcohol. Hydroylized alcohol product is typically in the 87% to 99% range (converted PVA). It was discovered in Germany by Dr. Fritz Klatte in 1912.