Performance Characteristics of Materials

Performance Characteristics of Materials

• This topic covers the properties of wood, plastics, and metals.
• Key properties include strength, toughness, ductility, malleability, and more.
• Textbook pages 25-31

Learning Outcomes

• Identify material characteristics (wood, plastic, metal)
• Describe characteristics, testing methods, and relevance
• Explain material use based on characteristics

Conductivity (a)

• Electrical resistivity measures a material's opposition to current flow.
• Low resistivity means the material easily allows current flow.
• Resistivity is represented by the Greek letter ρ.
• Examples measured with ring and test rig include thermal conductivity, specific heat capacity, and density of polystyrene foam, pine wood, rubber, stainless steel, aluminum, gold, and copper.

Strength (b)

• Strength of materials (mechanics of materials) studies how solid objects react to stress and strain.
• Types of stresses include tension, compression, torsion, shear, and bending.
• Images show stress types, steel girders with expansion joints, and smart plastics.

Materials Testing for Strength

• Compression: Measuring resistance to inward forces, tested with Ametek.
• Tension: Ability to withstand stretching forces. Tested using a Universal Testing Machine.
• Torsion: Ability to withstand twisting forces.
• Shear: Measuring ability to withstand forces applied at both ends.

Elasticity (c)

• Elasticity is the ability of an object to return to its original shape after stretching or compressing.
• While rubber bands are a good example of elasticity, this property applies to wood, plastics, and metals.
• An example is the steam-bent walnut furniture.

Plasticity (d)

• Plasticity is the ability of material to be shaped or molded.
• Images show examples of thermo-plastic polymers, steel, and timber-ceramic composites.

Malleability (e)

• Malleability is the ability of a substance to deform under pressure.
• Malleable materials can be flattened into thin sheets with hammering or rolling.
• Many metals with high malleability also exhibit high ductility.
• Copper is a good example of a malleable material, useful for plumbing.

Ductility (f)

• Ductility is the ability of a solid material to stretch into a wire under tensile stress.
• Ductility is measured by percent elongation or area reduction from a tensile test.
• Examples in images show how a material stretches.
• Significant elongation is about 5.0% according to Shigley's Mechanical Engineering Design

Hardness (g)

• Hardness measures resistance to plastic deformation (indentation or abrasion).
• Materials like metals are generally harder than plastics or wood.
• Rockwells scale is a hardness scale based on indentation hardness, measuring depth of penetration under load.

Toughness (h)

• Toughness is a material's ability to absorb energy and deform plastically before fracturing.
• It's the amount of energy per unit volume absorbed before rupturing.
• An IZOD impact test rig is shown.

Durability (i)

• Durability is a product's ability to remain functional without excessive maintenance.
• Plastics can be problematic due to their durability leading to worldwide pollution.
• Examples include a chart showing the durability of timber.

Biodegradability (j)

• Biodegradability means organic substances breaking down into simpler substances via microorganism enzymes.
• Complete breakdown yields inorganic molecules like water, carbon dioxide, and methane.
• Examples of biodegradable materials include PLA, PHB, starch, sugar, cellulose.

Biodegradable Materials (additional notes on page 14)

• Biodegradable materials decompose rapidly with microorganisms.
• Examples include food scraps, cotton, wood, and some manufactured products.
• Future products should be designed for recycling using bio-degradable materials.