Chapter p

Since the time of prehistoric Man, humans have been manipulating different materials to build tools and structures to live in. The most common materials are: Wood Ceramics Metals Alloys Plastics Modified Wood Composites

HISTORY of MATERIALS (do not copy) Different types of rock were used to build initial tools and wood was most likely one of the first materials used to build dwellings and furniture. Ceramic structures have been found in many historical digs. The earliest ceramics were pottery articles made from clay.

HISTORY (Continued) The arrival of plastics many centuries later were very significant in the advancement of the use of material. With time, composites were added to the mix allowing the advancement of the manufacturing of technical objects.composites

WOOD p Primary material used by man for construction and heating. 2 types of wood: –Hardwood –Softwood The following properties greatly influence the choice of wood for construction: –Hardness * low thermal/electrical conductivity –Elasticity * pliability and ability to be shaped –Colour & shades * texture and grain –Resilience and toughness * weight

Modified wood consists of wood and additional products such as glue, plastics and preservatives. Some examples: Plywood Particle board Fiber board Since wood is an organic substance it tends to degrade very rapidly. Products such as paint, stain, hardeners and varnish, protect the wood from weathering and infestation.

CERAMICS p Ceramics have low electrical conductivity properties, thus making great insulators for electrical circuits. Their durability and hardness make them very useful for construction - bricks, ceramic tiles, carbide blades, etc.

Ceramics are very heat resistant and this makea them appropriate for kitchen appliances such as ovens and heating dishes. Ceramics do not corrode and therefore are very useful for ducts and drains. Just the same, ceramics are fragile and can be easily broken. Care must be taken in the choice of raw material and the method for baking. Certain acids and bases (sulfuric acid and calcium hydroxide) can degrade ceramics. Extreme changes in temperature may also crack and destroy ceramics.

METALS p Metals are made from extracts from mineral ore and are often shiny. This material displays good thermal and electrical conductivity. Many are valued for their malleability (pliability) and ductility (deform under tension - stretch). Since metallic substances are rarely pure in nature, they are often classified as alloys. They are produced because of their density, reactivity, electrical and thermal conductivity, and tensile strength and shear strength. Corrosion is caused by oxidation of the substances. Coating and surface treatments usually increase the life of the material and decrease degradation.

Alloy: A mixture of a metal with one or more other substances, which can be metal or nonmetal. coppercopper, magnesium, manganese, silicon and zinc.magnesiummanganesesilicon zinc

PLASTICS p Plastics are often produced from fossil fuels such as petroleum and natural gas. Plastics can be molded because they are malleable. Thermoplastics –Do not undergo chemical change when heated –Can be molded over and over again –Can be manipulated (molded) when heated –When cooled, the structure holds its shape –Not biodegradable but most can be recycled

Thermosetting plastic –Always remains hard even when heated –Once it take shapes its form can not be altered –If overheated it will decompose –Melamine and polyesters (nylons) are examples –Harder and more resilient than thermoplastics –In Quebec cannot recycle thus have negative effects for the environment –Poor conductors Degradation –Appears as cracks or change of color –Degradation is irreversible –Affected by certain liquids like acids, oxidation and ultraviolet rays from the sun –Addition of waterproof coatings, antioxidants and pigments can reduce degradation and protect the plastic

COMPOSITES p Made from two or more materials from different categories. Two main components: –Matrix (original material) that forms structure –Reinforcement (inserted into matrix to strengthen it) Degradation –Deformation or fracture –Avoid extremes: shocks, impact, repeated stress –Do not survive in corrosive solutions

MECHANICAL PROPERTY p. 388 The term Mechanical Property defines how a material will respond when subjected to different forces and constraints. The most common mechanical properties are: Elasticity Malleability Stiffness Hardness Resilience Ductility Other properties are also very important to consider when choosing a material for construction: Electrical Thermal Resistance to corrosion Ex: If a car company is planning a new model of vehicle they will try to choose a material for the body structure that will be resistant to road salt and therefore rust. The use of different metalloids for hubcaps is a good example.

The study of stress factors and their effects on materials will help determine the suitability of a particular material for a specific manufacturing project. Manufactures refer to the word constraint when considering stress factors.

Main types of Constraints p. 387 Tension or tensile (pulling) Compression (pushing) Torsion (twisting) Shearing (cutting) Deflection (bending) Temperature(which can cause deformation)

Types of Deformation p. 387 FRACTURE: is when the force being applied is large enough to break the object. ELASTIC: The constraint changes the form of the material but once the force is removed the materials returns to its original shape. PLASTIC: the force causes a permanent deformation that remains even when the the force is removed.

Mechanical Properties of Materials Mechanical PropertyDefinition HardnessAbility to resist indentation or abrasion ElasticityAbility to return to original shape after undergoing a constraint ResilienceAbility to resist shocks without breaking DuctilityAbility to be stretched without breaking MalleabilityAbility to be flattened or bent without breaking StiffnessAbility to retain shape when subjected to various constraints

**Degradation of a Material: Is the decline in some of its properties due to the effects of the surrounding environment.

**Protection of a Material: Is the application of procedures that prevent or delay its degradation.