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1.1 Materials & Their Applications, Polymers, Destructive Testing,…
1.1 Materials & Their Applications
Materials & Applications
Material Properties
Physical - structure of material
transparent - all light gets through easily
density - mass per unit vol
Transluscent - some light gets through (frosted glass)
Fusability - how easily it changes state
Opaque - no light gets through
Magnetism - natural forces between objects that allow it to attract iron
Thermal expansion - increase vol because of heat
Corrosion Resistance - withstands environment
Thermal - conductor/insulator - allows/not transfer of heat
Electrical - conductor/insulator - allows/not current to flow
Mechanical - how material reacts to external forces
Hardness - resist abrasion with no fracture
Toughness - absorb impact
Torsional - resist twisting
Plasticity - permanently deformed
Shear - resist friction
Ductility - drawn out under tension - stretch wire
Bending - resist bending
Malleability - withstand deformation, increases with temperature
Tensile - resist being stretched
Elasticity - deformed then returned to original shape
Compressive - withstand being crushed/shorterned
When determining material, designers must find balance between these factors for function of the material.
Selection is not easy & often compromises have to be made
Final product often is influenced by product function and material properties
Designers must consider; cost, aesthetics, disposal, manufacturing processes. e.g. stainless steel vs LCS
Stock form is a set of standard sizes materials come in, eg MDF
Methods for Investigating & Testing Materials
We must ensure all variables are the same; Size of Sample, external conditions, testing equipment, force applied + method of it + position of it, the individual taking measurements
Polymers
Elastomers - at room temp they can be deformed under pressure and returns to original shape when no force, weak bonds - stretch easily e.g. NATURAL rubber, Silicone, Neoprene
Thermosetting - cannot be reheated and reshaped, chemical change when heated - molecules form rigid cross links e.g. U/MF - Urea/Melamine Formaldehyde, polyester & epoxy resin
Thermoplastic - repeatedly reheated and shaped, recyclable, long linear chains, held by van de Walls forces e.g. L/H density polyethylene(L/HDPE), Polypropylene (PP), High impact polystyrene (HIPS)
Why polyethylene terephthalate for drink bottle; thermoplastic - recylable, tough, transparent, impermeable to CO2, pigmented
Why Melamine formaldehyde for kitchen worktop; thermosetting - not affected by hot pans on surface, chemical resistant, hard, can be pigmented
Why neoprene for wetsuit; elastomer - stretches around body, degradation resistant, can be pigmented
Destructive Testing
Hardness Testing
Workshop; Abrasion & indents, run file over material, dot punch material
Industrial; Rockwell + Vickers Pyramid = Force applied to material using diamond indenter, preload - force - zero reference position, load is added and left for set time. load is released. distance between preload and load is measured, smaller indent = harder material, Vickers is same just for hard materials and there is no preload. Brinell = Steel ball forced into material with pre-set load, diameter is measured, smaller diameter = harder
Toughness Testing
Workshop; Impact absorbed, clamp into vice, hit with hammer with the same force
Industrial; Izod impact test, notched test piece, pendulum hits into this and swings past, less swing after means more energy has been absorbed - tougher
Malleablility & Ductility Testing
Workshop; Secure into vice, bend 90 degrees, cracks on outside = lack of ductility, cracks on inside = lack of malleability.
Industrial; Test piece placed into bend machine and supported at both ends, plunger is set at a certain angle in centre and pushes till it breaks or fully bends. checked for cracks/defects. outer bend cracks = ductility, inner bend cracks = malleability
Tensile Testing
Industrial; put into tensometer machine - clamped, one clamp is fixed, the other pulls on the test piece, load vs distance is plotted on graph, shows information about
Workshop; clamp material into vice, apply load to end, how much material deflects under load.
Corrosion Testing
Workshop; Place outside and leave, inspect for surface corrosion
Conductivity Testing
Electrical; Multimeter, set distance, attach probes from Multimeter, higher resistance = less conductivity
Woods
Classification of Materials
Material Disposal
if not recyclable, environmentally aware customers may be influenced. e.g. bike frame - aluminium vs CFRP, CFRP is lighter and has more performance but it is not easily recycled
Hardwood - Deciduous trees, Expensive, Loose leaves in Autumn e.g. Oak, Teak, Birch, Ash
Softwood - Coniferous trees, cheap, evergreen trees e.g. Pine, Spruce, Cedar
Manufactured Boards - man-made wood based composite material, available in larger sizes e.g. MDF, Plywood, Chip Board, Aeroply
Why Teak for a bench; Natural Oils - resists corrosion/abrasion, aesthetic, hard
Metals
Ferrous - Mostly Iron/Carbon, magnetic, can rust. E.g. Low/Medium Carbon Steel, Cast Iron
Non-Ferrous - No Iron, not magnetic, cannot rust (can corrode) E.g. Aluminuim, Copper, Zinc, Gold, Silver, Lead, NIckel
Alloys - Two or more metals/elements, can be catagorised as non/ferrous, e.g Stainless Steel (F), Bronze (NF)
Why Aluminium for a can; Malleable - go into shape, Lightweight, Food safe, Non-ferrous - water goes into the can, Recyclable, Aesthetics
Non-Destructive Testing - products likely to have internal defects
Ultrasonic Testing
transducer pumps sound waves into material, intensity of sound waves are reflected back and recorded on display unit, waves travel through material and reflect any defects in material, sound energy is partially reflected and displayed on unit, used in aerospace + check quality of welds in pipes
Xray Testing
Xray beam passes through material, image is projected onto screen. microfocus x-rays allow observations in material, magnified images allow for minute flaws to be detected. used to inspect integrated circuits, printed circuit boards. checks for micro voids in composite materials - f1 cars where there is monocoque (single shell) construction
Conductivity
Thermal; heat flow meter, material is placed between 2 temp controlled plates. Temp increases at controlled rate. heat flow through is measured by sensors on surface of material
Electrical; 4 small diameter wires are stretched parallel across non conductive polymer blocks, held in place and connected to copper block terminals, 2 leads attach outside wires and is connected to precise current, 2 connect inside wires and measure pd drop, V=IR to get resistance
Paper Boards
compliant materials- can be scored, folded and cut with basic tooling to form items for packaging e.g. corrugated card, tracing paper, bleed proof paper, treated paper, duplex card
Why corrugated card for take-away food container; compliant, food safe, insulating, lightweight, recyclable, biodegradable
Composites
Made of 2 or more different materials resulting with material with enhanced properties e.g. Carbon Fibre Reinforced Plastic (CFRP), Glass Reinforced Plastic, Concrete, Engineered Wood - Glulam, Tungsten Carbide
Why GRP for boat hull; can be pigmented, chemical resistant, tough, allows for complex 3D shapes - layup method - manufactured
Smart Materials
material whose physical properties change due to change in environments. e.g. shape memory alloys (SMA), thermochromic pigment/film. phosphorescent pigment - glow in dark
Why thermochromic film for thermometer; changes colour in response to temp, red for hot, non toxic, can be a film strip, so its flexible and easy to put on a forehead
Modern Materials
Materials developed through invention of a new/improved process, e.g. Kevlar, precious metal clay, high density modelling foam, polymorph