Core 4 Flashcards
What are physical properties?
Properties that can be determined without damage or destruction and relate to the interaction of the material with energy and matter in its various forms.
Mass (kg) - Mass is a measure of the amount of matter a body contains.
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Weight (N) - Weight is a force and represents the mass of an object acted upon by gravity.
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Electrical resistivity (σ) - This refers to the ease with which electrons move through a material.
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Thermal conductivity (W.m^-1.K^-1) - A measure of the efficiency with which thermal energy will travel through a material.
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Thermal expansion (m.m^-1.K^-1) - describes how the size of an object changes with a change in temperature.
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Hardness - The resistance of a material to scratching or abrasion. A composite of:
- Yield Strength
Stress where material deforms permanently, beginning plastic deformation.
- Work Hardening
Material strengthening through plastic deformation, increasing resistance to further deformation.
- True Tensile Strength
Maximum stress material withstands considering actual area reduction during tension.
- Modulus of Elasticity
Measures material’s stiffness, ratio of stress to strain in elasticity.
What is hardness and the tests for hardness?
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A measure of the resistance to localized plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by pressing or abrasion.
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Test: Scratch Hardness
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Assesses material’s hardness by applying steady pressure from an indenter, measuring depth or size of indentation. Resistance to being scratched, developed in 1812.
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Test: Static Indentation Hardness
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These tests typically involve the penetration of an indenter into the test surface using low loading rates.
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Test: Dynamic Hardness
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Evaluates hardness by applying impact force, observing rebound or penetration, reflecting material’s resilience to sudden stresses. Use high rates of loading.
What are mechanical properties?
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Properties that relate to the way in which the material responds to the application of a force.
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Tensile & compressive strength - A measure of a material’s resistance to plastic deformation from a tensile or stretching type load - The ultimate tensile stress is the maximum tensile strength, this is the number that we measure for when testing this.
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Stiffness - The resistance of an elastic body to deflection by an applied force.
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Toughness - The ability of a material to resist the propagation of cracks.
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Fracture Toughness - Relates to the size of the crack that may be present before fracture will occur.
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Ductility - The ability of a material to undergo plastic deformation by extrusion or the application of tensile forces.
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Elasticity - A measure of a material’s ability to stretch under load and then return to its original dimensions after removal of that load.
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Plasticity - Elasticity of a material is associated with elongation behaviour that exceeds the elastic region.
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Young’s modulus - Measure of the stiffness or rigidity of a material. It describes how much a material will stretch or compress when a force is applied to it.
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Stress - A measure of the force being applied per unit area. (Stress = force / area)
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Strain - A measure of change in length occurring when under stress, divided by the unit length.
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*Stress and strain have true values which involve the instantaneous csa or length but more difficult to measure.
What are the aesthetic characteristics of materials?
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Taste: 1
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Sweet, sour, bitter, salt, and umami.
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Taste: 2
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Human taste in a style, aesthetic, colours, etc.
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Hearing
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Different pitch, timbre, tone, clarity, volume, frequency and decay.
Certain types of sounds can invoke different types of thoughts and feelings by the brain.
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Smell
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Response to scent is largely learned with life experiences and emotions. Smells are subjectively pleasant across cultures.
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Appearance: colour
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Colours, in their different shades and vibrances, like sound, can also invoke a variety of different emotions when processed by the brain.
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Appearance: shape
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The shape, and surface can change a products appeal and vary how people view it.
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Texture
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What are the smart materials? Their properties? and the 5 smart materials learnt?
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Materials that can respond to external stimuli or changes in their environment and exhibit specific, reversible changes in their properties.
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Responsiveness, reversibility, adaptability
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Piezoelectricity
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Material that responds to an application of an applied stress by producing a small electrical discharge and vice versa.
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Shape memory alloys
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Capable of changing shape and size in a predetermined manner by undergoing a solid-state phase change.
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Photochromic
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Undergo a reversible photochemical reaction that results in darkening proportional to the level of exposure to UV light.
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Magnet/Electro-rheostatic
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Fluids that can undergo changes in their viscosity, becoming semi-solid when exposed to an electric or magnetic field
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Low toxicity
Non-abrasive
Non-corrosive
Long storage life
Long working life
High boiling point
Low freezing point
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Thermoelectricity
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Exhibit the feature that when exposed to temperature differential, an electric potential is created and vice versa.
What is an ore? What are the processes surrounding them?
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Most metals are naturally found as ores, which means they contain impurities of other elements such as oxide, carbonate, or sulphide.
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Ores can be smelted over intense heat to separate them into the impurities that make them up thanks to unique melting points.
Explain grain and grain size in metals.
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When most solids form, they generally do so by arranging themselves in a regular pattern of atoms, a regular 3D arrangement known as collections of crystal structures. All metals solidify as collections of crystals (aka grains).
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The crystal structure of a metal reflects its properties.
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As a metal solidifies, these crystals form and grow. Eventually, different crystals will collide and intersect at different angles/patterns.
This region of mismatch is known as the crystal or grain boundary.
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Hence, grain size refers to the average size of the individual grains that make up the microstructure.
What are the four ways of modifying the mechanical properties of metals?
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Alloying
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elements other than those of the base metal are intentionally incorporated into the crystal lattice of the base metal. This results in the presence of more than one crystal structure.
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Used to to gain more desirable characteristics in a metal such as improved strength, corrosion resistance, hardness, or other properties.
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Work hardening (cold working)
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strengthens a metal by deforming it through processes such as rolling, hammering, or bending, typically at room temperature.
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introduces dislocations in the metal’s crystal structure, which makes further deformation more difficult, thereby increasing the metal’s strength and hardness.
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Tempering
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ferrous alloys such as stainless steel undergo a hardening heat treatment, in which an item is raised to an elevated temperature and cooled rapidly by plunging it into a suitable quenching medium.
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Hardness and strength are significantly increased, however, there is an accompanying decrease in ductility and impact toughness.
What are superalloys? What criteria must they meet?
Feature excellent high-temperature creep resistance, resistance to thermal shock and high-temperature oxidation resistance.
These alloys are well known for their ability to operate at high temperatures while maintaining strength.
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Creep resistance: creep is the tendency of a solid material to undergo slow deformation while subject to persistent mechanical stresses.
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Thermal shock resistance: ability to withstand sudden and extreme changes in temperature without cracking or failing.
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High-temperature oxidation resistance: ability to resist oxidation at elevated temperatures when exposed to oxygen.
What are the applications of superalloys?
Iron-nickel based superalloys
- Cryogenics
- Jet engine components
- Petrochemical processing
machinery
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Cobalt-based superalloys
- Turbine blades
- Orthodontic wires
- Biomedical implants
- Food processing equipment
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Nickel-based superalloys
- Air scrubbers
- Marine applications
- Gas turbine components
Discuss the recovery and disposal of metals and metallic alloys.
Recycled steel can be used in place of virgin iron, resulting in 60% energy savings in comparison to extracting more iron ore.
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Aluminium is one of the most energy-intensive materials to produce and the largest electrical energy consumer of all industries. Recycled aluminium however requires less than 6% of the mined alternative.
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E-waste is often shipped off to be dealt with in developing countries where it can pose major health problems if allowed to leach into the environment (lead, arsenic, mercury). It contains many expensive materials such as platinum and silver, its recovery could offer considerable cost savings.
Discuss the characteristics of softwood, hardwood and man-made timbers.
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Softwood
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- simpler structure, containing a single cell type.
- made up of long pores (Tracheids) which act as fluid transport.
- Typically conifers, have needle-like leaves and form cone seeds.
- Usually lighter in colour, found in cooler climates.
- Grow much faster due to the way nutrients are transported
- Lower densities and reduced hardness however this does not stay true for all examples.
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Hardwood
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- Made up of two cell types, fibre and vessel.
- Fibers provide strength and structural support. Tough and resistant to bending. Long and slender, interlocking.
- Higher fibers content generally means more durable the wood is.
- Vessel cells form the water-conducting system. Large and cylindrical with thin walls. Arrange end to end to form tubes.
- Broad leaves which are lost in winter. Seeds enclosed in fruits. Can be evergreen or deciduous.
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Man-made timbers
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- Composite products that use wood lengths, fibres and veneers with adhesive binder, combined under heat and pressure.
Give examples of hardwoods, softwoods and man-made timbers.
HW: Oak, mahogany, beech, walnut, balsa.
SW: Pine, cedar, spruce, redwood.
MMT: Plywood, MDF, chipboard, LVL
What unique characteristics do MMTs exhibit?
Uniformity of properties, its properties stay true regardless of environment.
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Greater availability of product sizes and shapes.
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Lower cost compared with solid natural timbers of the same dimensions.
What factors affect the strength of timbers
Duration of loading: a decrease in strength due to extensive load
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Defects: knots, splits, shakes etc - disrupt grain flow
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Chemical treatment: adverse effect on mechanical properties
especially water-based preservatives
Explain seasoning and why it is used.
Moisture must be removed before use without causing splitting or warping.
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If moisture is below 20%, timber will decay.
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Seasoning can be done by air or by kiln.
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Air seasoning
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Stacked in a way that allows air circulation on all sides
Shield the timber from rain but allow air to flow freely
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Several months, slow
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Low-cost, low energy use, environmentally friendly
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Kiln seasoning
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Stacked in a kiln where air circulation, temperature, and humidity can be precisely managed.
Begins with lower temperatures and higher humidity, which are gradually adjusted to avoid rapid drying that might cause cracking or warping.
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Days or weeks, fast, quality control
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Higher cost and energy use.
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Correctly seasoned timber is:
- Strong
- Stable
- Resistant to decay
- Easy to paint, glue, nail, screw and machine.
What processes are involved with finishing timbers?
Treatment
can involve solutions which make the wood poisonous to insects, fungus, and marine borers as well as protecting it from the weather.
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generally, timbers which are to be positioned outside should make use of a treatment.
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Finishing
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Finished timber requires sanding and one of the following:
- Stain
- Paint
- Shellac
- Wax polish
- French polish
- Plastic varnish
Explain what the different finishes do.
Discuss deforestation and reforestation.
The timber industry is a big part of the reason for deforestation.
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Discuss glass. What are its characteristics?
This sort of glass is relatively soft. To give the glass stability and hardness, materials such as limestone and dolomite are added. Scrap glass can also be added to make the process more economical.
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The main types of glass are glass fibre, lead glass, soda-lime glass, and borosilicate glass.
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- Transparency
- Chemically Inert
- Non-toxic
- Hardness
- Brittle
- Aesthetic Versatility
- Electrical Insulator
- Cheap
What are the applications of glass? Link to its characteristics.
Fibre optic cables
Food and chemical containers
Containment of nuclear waste (Vitrification)
Protective layer in solar cells
Cookware and lab equipment
Scratch-resistant glass in displays
Decorative glassware
Discuss the recovery and disposal of glass.
When collected for recycling, glass is separated by colour, crushed, and remelted for use in new glass containers.
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Environmental benefits of reducing quarrying and reduced energy usage as cullet melts easier.
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Cullet needs to be in the right condition to be used, i.e. free from impurities.
What is the structural difference between thermoplastics and thermosetting plastics?
Thermoplastics: Linear or Branched Polymer Chains
long, linear or branched polymer chains. Weak intermolecular forces hold these chains together without chemical bonding between them.
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weak forces between chains allow the chains to move past each other easily when heated, so they can be repeatedly melted and reshaped.
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When the material cools, these chains return to a solid form without altering the chemical structure, allowing thermoplastics to be re-molded multiple times.
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Examples: Polyethylene (PE), Polypropylene (PP), and Polyvinyl Chloride (PVC).
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Thermosetting Plastics: Cross-Linked Polymer Network
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Cross-linked, three-dimensional network of polymer chains. Curing, these chains form covalent bonds between them, creating a rigid structure.
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Highly stable and resists movement, making thermosetting plastics hard and rigid.
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Structure is permanent and cannot be reshaped by heating; if heated further, thermosets will decompose rather than melt.
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Structure provides high resistance to heat, chemicals, and wear.
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Examples: Epoxy resin, Bakelite, Melamine, and Phenolic resin.
