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Parts of objects can be subjected to one or more external FORCES Remember forces? An action that can change the motion of an object, or deform the object, by pushing or pulling on it.

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Materials tend to be deformed by forces A constraint describes the effect of external forces on a material Compression, tension, torsion, deflection, shearing

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Other types of compression: Compression shorts for sports Squeezing a wet sponge Crushing a pop can

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Other examples: Copper stretched into a wire Two teams of tug-of-war

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Examples: An earthquake twisting a bridge Hands wringing a wet towel

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What other examples can you think of?

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Scissors and metal cutters

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Three types: elastic, plastic, fracture ELASTIC: temporary change in shape PLASTIC: permanent change FRACTURE: breakage

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Plastic deformation of piece of railway track

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before and after

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The mechanical properties of a material describe how it reacts when subjected to one or more constraints Hardness, elasticity, resilience, ductility, malleability and stiffness

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Hardness is the ability to resist indentation or abrasion

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Elasticity is the ability to return to their original shapes after undergoing a constraint

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Resilience is the ability to resist shocks without breaking

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Ductility is the ability to be stretched without breaking The opposite of ductile is brittle

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Malleability is the ability to be flattened or bent without breaking

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Stiffness is the ability to retain shape when subjected to various constraints

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Resistance to corrosion electrical conductivity thermal conductivity

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Ability to resist corrosive substances (water, salt, fumes) which can cause damage like rust

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Ability to carry an electric current

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Ability to transmit heat

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Degradation of a material is the decline in some of its properties This is due to the effects of the surrounding environments climate, humidity, chemical Examples : old photographs, rust on cars What else degrades over time?

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We can protect material by treating the material Rust-proofing of cars 2 ways

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Wood Ceramics Metals and alloys Plastics Composites

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Wood comes from trees! There are 2 types of wood : hardwood and softwood Categorized based on their hardness Hardwood : maple, oak (deciduous trees) Softwood : pine or spruce (conifers)

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Considerations: Species of tree used Speed of growth and injuries Water content

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Hardness, elasticity, resilience and toughness Low thermal conductivity

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Made from wood, glue, plastics and preservatives Modified wood is treated wood or a material made from wood mixed with other substances Plywood, particleboard and fibreboard Why do we need modified wood? Arent the trees good enough?

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Resistance to cracking, shrinking and twisting/warping, it is very strong Layers are glued together, grain opposite (perpendicular grain)

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Made from wood particles like wood chips and shavings and sawdust Pressed together with resin Cheap to make, very dense, not as strong as plywood

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sometimes called MDF for medium density fibreboard Made from wood fibers by breaking down the hardwood or softwood and mixing it with wax and resin It is denser than plywood Used in manufacturing of furniture More dense than particle board

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Wood can degrade quickly because it is organic We treat wood to prevent it from rotting The wood can be dipped in an alkaline solution containing copper : greenish wood Also can heat wood to a very high temp, expensive treatment

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Dipped wood for deck building Heat treated wood for flooring

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Made from heating oxides like SiO 2 When the raw material is heated, the water evaporates and the bonds between the compounds are rearranged Ceramics are always solid at room temperature

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Traditionally clay and sand

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Low electrical conductivity, used as insulators High degree of hardness used for bricks & building materials like tiles and also as cutting tools Heat resistant and low thermal conductivity so used a lot in the kitchen, dishes, ovens Resistant to corrosion Fragile, can break easily unless treated

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Quite durable, think archaeological digs Strong acids and strong bases can degrade ceramics significantly (Breaking Bad season 1 bathtub scene?) Can deteriorate with sudden thermal shock Glass is a type of ceramic

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Pot-in-pot refrigerator Zeer fridge Easy to make, very efficient, cheap!

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METALS METALS are made from mineral ore, shiny Good thermal and electrical conductivity Some are ductile and malleable ALLOYS ALLOYS are a mixture of a metal with one or more other substances which may be metallic or non-metallic Metallic materials are rarely pure metal

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Ferrous means with iron, examples are cast iron and steel Nonferrous without iron, examples are aluminum alloys, brass, bronze

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Main degradation is oxidation which causes corrosion They are treated with coatings Coating can be metallic (zinc, chrome, gold, silver, nickel, aluminum, lead) Coating can be non-metallic (paint, enamel, grease, resin)

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An alloy made mostly from iron and carbon Heat treated

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Made from petroleum and natural gas Made of polymers and other substances Two types THERMOPLASTICS and THERMOSETTING PLASTICS

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Plastic that becomes soft enough when heated to be molded or remolded and that hardens when cooled to hold its shape of plastics are thermoplastics Containers Recyclable (codes 1-6)

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What else can you think of?

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These plastics remain hard even when heated If heated to its decomposition temp (max temp) then it will decompose Melamine, polyester Harder and more resilient than thermoplastics Not recyclable Kayaks, cafeteria trays

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Famous Kingston Penn escape done with cafeteria trays!

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Cracks can form over time along with colour fading Slow degradation but irreversible Different methods of protection include waterproofing, antioxidant additions, pigmentation

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composites

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Formed by combining materials from different categories to obtain material with enhanced properties 2 main components : matrix and reinforcement

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No not the movie The matrix is the skeleton of the material and gives it shape It surrounds and supports the reinforcements The reinforcements are inserted into the matrix to strengthen it

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Plastic reinforced with fiberglass is used in airplanes: plastic is the matrix and fiberglass is the reinforcement The properties of the two are combined to obtain a material that is stiff and resilient

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Aerospace Sports arts/music instruments Engines and braking systems for high performance Military and police bullet proofing

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Deformation or fracture of matrix Loss of adherence between matrix and reinforcement Protection by testing for correct material mix and testing for adherence in conditions present

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worksheet