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Materials

Materials. Materials : constraints and deformations. 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. Constraints and deformations.

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Materials

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  1. Materials

  2. Materials : constraints and deformations • 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.

  3. Constraints and deformations • Materials tend to be deformed by forces • A constraint describes the effect of external forces on a material • Compression, tension, torsion, deflection, shearing

  4. Compression: forces that tend to crush Other types of compression: Compression shorts for sports Squeezing a wet sponge Crushing a pop can

  5. Tension: forces that tend to stretch Other examples: Copper stretched into a wire Two teams of tug-of-war

  6. Compression vs tension

  7. Torsion: forces that tend to twist Examples: An earthquake twisting a bridge Hands wringing a wet towel

  8. Deflection: forces that tend to bend What other examples can you think of?

  9. Shearing: forces that tend to cut Scissors and metal cutters

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

  11. Elastic deformation

  12. Plastic deformation Plastic deformation of piece of railway track

  13. Fracture deformation before and after…

  14. Correct activity 48

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

  16. hardness Hardness is the ability to resist indentation or abrasion

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

  18. Resilience Resilience is the ability to resist shocks without breaking

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

  20. malleability • Malleability is the ability to be flattened or bent without breaking

  21. stiffness Stiffness is the ability to retain shape when subjected to various constraints

  22. Other properties • Resistance to corrosion • electrical conductivity • thermal conductivity

  23. Resistance to corrosion • Ability to resist corrosive substances (water, salt, fumes) which can cause damage like rust

  24. Electrical conductivity • Ability to carry an electric current

  25. Thermal conductivity • Ability to transmit heat

  26. Degradation and protection • 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?

  27. How can we counteract degradation • We can protect material by treating the material • Rust-proofing of cars – 2 ways

  28. degradation

  29. Categories of materials • Wood • Ceramics • Metals and alloys • Plastics • Composites

  30. Wood and modified wood • 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)

  31. Properties of wood Considerations: • Species of tree used • Speed of growth and injuries • Water content

  32. Other properties to consider • Hardness, elasticity, resilience and toughness • Low thermal conductivity

  33. Modified wood • 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? Aren’t the trees “good enough”?

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

  35. particleboard 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

  36. fibreboard 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

  37. Degradation and protection of wood and modified wood • 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

  38. Treated wood Heat treated wood for flooring Dipped wood for deck building

  39. Ceramics • Made from heating oxides like SiO2 • When the raw material is heated, the water evaporates and the bonds between the compounds are rearranged • Ceramics are always solid at room temperature

  40. What goes ‘in’ to ceramics • Traditionally clay and sand

  41. Properties of ceramics • 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

  42. Degradation of ceramics • 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

  43. Ceramic fridge? Pot-in-pot refrigerator Zeer fridge Easy to make, very efficient, cheap!

  44. Metals and alloys • METALS are made from mineral ore, shiny • Good thermal and electrical conductivity • Some are ductile and malleable • 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

  45. Alloys – ferrous and nonferrous • Ferrous means with iron, examples are cast iron and steel • Nonferrous without iron, examples are aluminum alloys, brass, bronze

  46. Degradation and protection of metals and alloys • 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)

  47. steel

  48. steel • An alloy made mostly from iron and carbon • Heat treated

  49. plastics • Made from petroleum and natural gas • Made of polymers and other substances • Two types THERMOPLASTICS and THERMOSETTING PLASTICS

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