Unit 10 properties and applications of engineering material assignment 3 ralph timm PDF

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Unit 10:Properties and Applications of Engineering Materials

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Page 3/ 24 – Task 1 Page 25/30 – Task 2 Page 31/35 – Task 3 Page 36/38 – Task 4 Page 39 – Task 5

Bibliography: file:///G:/engineeirng%20level%203%20year%202/Wor%20Ralphy/Materials/assignment %203%20.pdf http://www.bodycote.com/en/services/heat-treatment/annealingnormalising/recrystallisation.aspx http://www.bpf.co.uk/plastipedia/processes/default.aspx http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/bonding/structure_properties rev3.shtml https://www.sglgroup.com/cms/international/products/product-groups/cc/carbon-ceramicbrake-disks/index.html?__locale=en http://ceramics.org/learn-about-ceramics/structure-and-properties-of-ceramics 1

https://compositesuk.co.uk/composite-materials/processes http://www.technologystudent.com/equip1/sma1.htm http://www.freestudy.co.uk/nc%20materials/outcome4t1.pdf https://www.researchgate.net/publication/229572320_Effects_of_Damage_on_Thermal_Sh ock_Strength_Behavior_of_Ceramics

Task 1: Identify and describe how the method of processing that material can affect the behaviour and the resulting properties: When a metal solidifies grains or crystals will be formed. The grains may be small, large or longer in size this depends on how quick the metal is cooled and what happened to it. If the metal is maintained at a higher temperature for a long period of time the crystals will consume each other and there will be fewer but they will become larger. When this happens it is called grain growth, the grain size and the direction can be changed by deforming the metal in a cold or hot state and this will affect lots of different mechanical properties of the metal. The properties which may be affected may be the hardness, strength and ductility. Heat treat will also affect the grain and properties. Slower cooling processes allows larger crystals and more rapid cooling promotes smaller crystals. 2

Some processes are as follows:  Cold Working  Annealing  Forging  Quenching  Tempering  Drawing Rigid materials; do not undergo any deformation under applied loads. Forming tools are assumed to be rigid in most sheet metal forming analyses for computational efficacy. A reasonable, although not 100% realistic assumption. Elastic materials; undergo a reversible deformation under applied loads. Sheet metals loaded below their yield stress show elastic behaviour. Observed elastic strains are due to temporary displacement of the atoms within crystal matrices, typically small for metals (0.002-0.005 or 0.2%-0.5%). Plastic materials; undergo permanent deformation that remains after the load removal. In all of the sheet metal forming processes, this behaviour is desired. After all, without plastic deformation, the parts would remain as flat sheets. Viscous materials; behaviour is dependent on the rate of deformation. In hot stamping, the yield stress of the sheet metals depends on the applied strain rate. When small loads (stresses) are applied to metals they deform, and they return to their original shape when the load is released. Bending a sheet of steel is an example where the bonds are bent or stretched only a small percentage. This is called elastic deformation and involves temporary stretching or bending of bonds between atoms.

When higher stresses are applied, permanent (plastic) deformation occurs. This plastic deformation involves the breaking of bonds, often by the motion of dislocations. Dislocations move easily in metals, due to the delocalized bonding, but do not move easily in ceramics. This largely explains why metals are ductile, while ceramics are brittle. If metals are put under too much stress or strain it will evidently cause failure.

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Cold working; this process leaves the surface clean, bright and accurate dimensions can be produced. If the metal is cold worked, this could make the material within the crystals becomes stressed and the crystals may be deformed. For example cold drawing will produce long crystals. In order to get rid of these stresses and to produce normal crystals, the metal can then be heated up to certain temperature where it will re crystallise. The new crystals will form and larger ones will then be reduced in size. Cold working a metal will also change the properties dramatically. An example of this is cold rolling of carbon steels this will create a stronger and harder steel, this is known as work hardening. Metals are malleable - they can be bent and shaped. This is because they consist of layers of atoms. These layers can slide over one another when the metal is bent, hammered or pressed.

Recrystallisation: Recrystallisation is a process accomplished by heating whereby deformed grains are replaced by a new set of grains that nucleate and grow until the original grains have been entirely consumed. 4

Recyrstallisation annealing is an annealing process applied to cold-worked metal to obtain nucleation and growth of new grains without phase change. This heat treatment removes the results of the heavy plastic deformation of highly shaped cold formed parts. The annealing is effective when applied to hardened or cold-worked steels, which recrystallise the structure to form new ferrite grains. Advantages:    

Allows recovery process by reduction or removal of work-hardening effects (stresses) Increases equaled ferrite grains formed from the elongated grains Decreases the strength and hardness level Increases ductility

Application of Material:  The annealing of stamped parts in cold-rolled steel is designed to produce a recrystallised ferrite microstructure from highly elongated, stressed grains resulting from cold work.  The annealing of forged parts is performed to facilitate subsequent operations, like machining or cold forming

Process Details:  Recrystallisation is usually accompanied by a reduction in the strength and hardness of a material and a simultaneous increase in the ductility. Thus, the process may be introduced as a deliberate step in metal processing or may be an undesirable byproduct of another processing step. The most important industrial uses are the softening of metals previously hardened by cold work, which have lost their ductility, and the control of the grain structure in the final product.  The recrystallisation temperature for steels is typically between 400 and 700 °C. The recrystallisation conditions, such as heating rate and soaking time depend on the degree of cold work and the steel composition

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Polymers: There are many methods that can be used to process polymers, some of these are as followers:  Blow Moulding  Injection Moulding  Casting  Rotational Moulding 6

 Compression Moulding Polymers can be used for plastic drinks bottles, plastic pipes and sheeting, they can be machined, fabricated and even welded using specialised solvent and using hot joining process. Thermosoftening polymers:

Thermo-softening polymers soften when heated and can be shaped when hot. The shape will harden when it is cooled, but can be reshaped when heated up again. Poly(ethene) is a thermo-softening polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material.

Thermosetting polymers:

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Polymer with cross-links Thermosetting polymers have different properties to thermo-softening polymers. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermo-set used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily. Polymers have properties which depend on the chemicals they are made from, and the conditions in which they are made. For example, polyethene can be low-density or highdensity depending upon the catalyst and reaction condition used to make it. The table summarises some differences in their properties:

Below I will explain the process of thermosetting polymer process. Plastics - or polymers - fall into two main groups: Thermo-softening plastics and Thermosetting plastics Thermoplastics can be made plastic and malleable at high temperatures. Modern thermoplastic polymers soften anywhere between 65 ºC and 200+ ºC. In this state they can be moulded in a number of ways: They differ from thermo-set plastics in that they can be returned to this plastic state by reheating. They are then fully recyclable.

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Thermo-set plastics differ in that they are not re-mouldable. Strong cross links are formed during the initial moulding process that give the material a stable structure. They are more likely to be used in situations where thermal stability is required. They tend to lack tensile strength and can be brittle.

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The manufacture of thermosetting plastics is usually a two stage process. First the, partially polymerised material is produced consisting of polymer chains. This raw material then undergoes final polymerisation during high temperature and pressure moulding process. This ‘cures’ the polymer by forming cross links – the chemical bonds between the chains that effectively produce a continuous three-dimensional polymer

Thermosetting plastics: Once 'set' these plastics cannot be reheated to soften, shape and mould. The molecules of these plastics are cross linked in three dimensions and this is why they cannot be reshaped or recycled. The bond between the molecules is very strong. Thermoplastics: These plastics can be re-heated and therefore shaped in various ways. They become mouldable after reheating as they do not undergo significant chemical change. Reheating and shaping can be repeated. The bond between the molecules is weak and become weaker when reheated, allowing reshaping. Thermoplastics tend to be composed of 'long chain monomers'. These types of plastics can be recycled. Many thermoplastics can be thermoformed, they include Polystyrene, Polypropylene, Apet, Cpet, and PVC. EVOH is commonly incorporated into a co-extrusion for its superior barrier properties in food. Co-extrusions of these materials are commonly used to provide precise properties for specific applications. The demands of the food packaging industry are for materials which resist the passage of odours, moisture and gases, hence the use of plastics with superior barrier properties.

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Ceramics: Dimensioning and Design The overall car braking system is designed to match a car´s layout and take advantage of the ceramic brake disk material´s properties. We cover the designing of the brake – the construction of the brake disk as well as the selection of the friction layers and the caliper – and adjust the brake into the concept of the vehicle. The main parameters determining the braking system design are a car´s maximum speed, the time sequence of full brake applications possible to bring a car to a stop from top speed and the mass to be braked, in addition to the axle load distribution and the car´s aerodynamics. The purpose of brake disk dimensioning and design is to ensure that a car can be stopped safely under any conceivable driving conditions. Braking system design also needs to ensure that neither the disk itself nor any other component in its direct vicinity is exposed to excessive thermal loads. The optimal cooling vane geometry is determined by numerical methods (Computational Fluid Dynamics) for each car model. The design calculation also takes account of the air pressure building up underneath the car and inside the wheel arch as a function of the car´s aerodynamic design and traveling speed.

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Material A special feature of carbon-ceramic brake disks is the ceramic composite material they are made from. Both the carbon-ceramic brake disk body and the friction layers applied to each side consist of carbon fiber-reinforced silicon carbide. The main matrix components are silicon carbide (SiC) and elemental silicon (Si). The reinforcement of the material is provided by carbon fibers (C). Silicon carbide, the main matrix component governs great hardness for the composite material. The carbon fibers make for high mechanical strength and provide the fracture toughness needed in technical applications. The resulting quasi ductile properties of the ceramic composite material ensure its resistance to high thermal and mechanical load. Carbon fiber-reinforced silicon carbide materials thus combine the useful properties of carbon fiber-reinforced carbon (C/C) and polycrystalline silicon carbide ceramics. The elongation at break of C/SiC materials ranges from 0.1 to 0.3%. This is exceptionally high for ceramics. The entire characteristic profile makes fiber-reinforced silicon carbide to a fist-choice material for high-performance brake systems: Particularly the low weight, the hardness, the stable characteristics also in case of high pressure and temperature, the resistance to thermal shock and the ductility provide long live time of the brake disk and avoid all problems resulting of loading, which are typical for the classic grey cast iron brake disks.

Production: The secret of the advantages of the carbon-ceramic brake disk is the unique production process over approximately 20 days. To produce carbon-ceramic brake disks, we use carbon fibers which are given a special protective coating and then cut into short fiber sections of defined thickness and length. The production process includes preparation of the fiber 12

mixture, the production process for the disk body and the bell mounting as well as the final machining of the assembled brake disk. The entire production process is monitored with various tests and ends with one final testing. The production process of the ceramic brake body continues with a perform pressed with binding resin to a so called green body which will be converted in the ceramic component by carbonizing at 900 °C and silicon zing at 1700 °C in high vacuum. The complex feature of the manufacturing process is the use of the “lost core” technology – a plastics matrix which defines the design of the cooling vane geometry and which burns out without residues at carbonizing – as well as the different fiber components of the brake disk body, the friction layers on the ring exterior side and the point-shaped abrasion indicators which are integrated into the friction layer. Product Development

A carbon-ceramic brake is developed in three main stages to match a car´s particular layout: numerical modeling, the construction and testing of prototypes, and testing on an actual car. The brake disk is first simulated numerically on the computer, using the car´s particular model data. The carbon-ceramic brake disk´s diameter, its thickness and the height of the friction path are only some of the parameters calculated on the computer. Calculations for assembled carbon-ceramic brake disks include the design of the bell connection. This is a highly demanding design task because of differences in coefficients of thermal expansion need to be compensated for at any operating temperature possible. The numerical model also provides the design of the cooling vanes configured to optimize fluid dynamics. In the second development stage, prototypes (test specimens) of the carbon-ceramic brake disks are constructed on the basis of numerical model results and bench-tested, together with the matching brake pads and calipers. In the third and final stage, the disk prototypes are tested on the car. They complete not only high-speed runs on a test circuit but also mountain pass descents and road tests. On these test runs, the driver evaluate brake behavior, in particular braking performance and braking comfort, and the computer provides a detailed analysis of measured results. Together with the bench test results, the car test runs determine whether a disk prototype can be approved or not.

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These six materials all go into the process of making ceramic brake discs;

Ceramics usually have a combination of stronger bonds called ionic (occurs between a metal and non metal and involves the attraction of opposite charges when electrons are transferred from the metal to the non metal); and covalent (occurs between two non metals and involves sharing of atoms). The strength of an ionic bond depends on the size of the charge on each ion and on the radius of each ion. The greater the number of electrons being shared, is the greater the force of attraction, or the stronger the covalent bond.

These types of bonds result in high elastic modulus and hardness, high melting points, low thermal expansion, and good chemical resistance. On the other hand, ceramics are also hard and often brittle unless the material is toughened by reinforcements or other means which would lead to fracture

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In general, metals have weaker bonds than ceramics, which allows the electrons to move freely between atoms. Think of a box containing marbles surrounded by water. The marbles can be pushed anywhere within the box and the water will follow them, always surrounding the marbles. This type of bond results in the property called ductility, where the metal can be easily bent without breaking, allowing it to be drawn into wire. The free movement of electrons also explains why metals tend to be conductors of electricity and heat.

General Comparison of Materials: Property

Ceramic

Metal

Hardness

Very High

Low

Elastic modulus

Very High

High

Thermal expansion

High

Low

Ductility

Low

High

Corrosion resistance

High

Low

Wear resistance

High

Low

Electrical conductivity

Depends on material

High

Density

Low

High

Thermal conductivity

Depends on material

High

Magnetic

Depends on material

High

High temperature strength

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Beginning with rare earth ore, high purity rare earth oxides are separated and refined.

Measurement and Raw Material: Additives such as rare earth metals, iron, cobalt and others are measured to produce the desired composition. The materials are then melted in a vacuum induction furnace as shown below.

Melting: The materials are exposed to high frequency and melted in an induction furnace.

Pulverization: After completion of various process steps, the ingots are pulverized into particles that are several microns in size. In order to prevent oxidation from occurring, the small particles are protected by nitrogen and argon. 16

Compacting a Magnetic Field: The magnetic particles are placed in a jig and a magnetic field is applied while the magnets are pressed into shape. Through this process, we achieve magnetic anisotropy. Two methods of pressing exist: perpendicular pressing where magnets are pressed in a perpendicular magnetic field and parallel pressing where they are pressed in a parallel field. Given an equal grade of magnet, the perpendicular press method will result in a higher performance magnet. However, ring magnets must be pressed using the parallel method.

Sintering: Ingots that have been pressed are heat treated in a sintering furnace. The density of the ingots prior to sintering is about 50% of true density but after sintering, the true density is 100%. Through this process the ingots' measurement shrink by about 70%-80% and their volume is reduced by about 50%. Aging the magnets after sintering adjusts the properties of the metals.

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Inspecting Magnetic Properties: Basic magnetic properties are set after the sintering and aging processes are complete. Key measurements including remnant flux density, coactivity, and maximum energy product are recorded. Only those m...