Materials

Spot the difference

1. The Manner in which atoms are chemically bound changes its

properties

A) Ionic vs. Covalent

B) Chiral Molecules (Mirror Molecules)

• E.g Limonene

• Carvone (Dill, Spearmint)

• Ibuprofen + vs. ibuprofen -

2. The way that the atoms are chemically bound together dictates the properties of a

material

Properties

Characteristics that will help determine how a given material will react to a constraint.

Properties• The reaction of a material to constraints depends on

its mechanical properties.

• Types of Mechanical Properties:– Hardness– Elasticity– Resilience– Ductility– Malleability– Stiffness

• Which properties do you believe were considered in the selection of the building material for the Victoria Bridge?

Definition of mechanical properties

• Hardness – Ability to resist indentation

• Elasticity: – Ability to return to their original shape

• Resilience: – Ability to resist shocks

• Ductility: – Ability to be stretched without breaking

• Malleability: – Ability to be flattened or bent without breaking

• Stiffness: – Ability to retain their shape when subjected to

many constraints

Definition of mechanical properties

• A material can also undergo chemical changes, such as rusting and corrosion.

Other properties• Resistance to corrosion:

– Ability to resist the effects of corrosive substances which cause the formation of rust, for example.

• Electrical conductivity:– Ability to carry an electric current

• Thermal conductivity:– Ability to transmit heat

3. Material properties dictate how a material will react under

specific constraints

Constraints

What external forces are at play?

Constraints• A constraint is the effect external forces

have on a material/object/system.

– Examples of constraints:• Pulling an elastic band• Squishing a sponge

Types of Constraints• There are 5 main types of constraints

– Compression– Tension– Torsion– Deflection– Shearing

Using the definitions soon to be provided, can you give a common everyday example for each of these constraints?

Types of constraints• Compression:

– When a material is subjected to forces that tend to crush it

• Tension– When a material is subjected to forces that

tend to stretch it

Types of Constraints• Torsion

– When a material is subjected to forces that tend to twist it

• Shearing– When a material is subjected to forces that

tend to cut it

• Deflection– When a material is subject to forces that

tend to bend it

Types of Constraints• Which constraints would a bridge most likely be

subjected? Explain your reasoning.

– 5 Constraint reminder:• Compression• Tension• Torsion• Shearing• Deflection

4. A material’s properties will also determine how the material will

deform (react under specific constraints) and degrade.

Deformation

Ways that materials react to the constraint

Deformations• A material deformation is the change in shape of

a material based on the constraints that are applied.

• There are three main types of deformations– Elastic– Plastic– Fracture

Using the definition soon to be provided, can you give a common everyday example for each of these deformations?

Types of material deformation

• Elastic:

– When the constraint leads to a temporary change in the shape or dimensions of the material.

– When the constraint is removed, the material returns to its original form.

Types of material deformation

• Plastic:– The constraint leads to a permanent

change in the shape or dimensions of the material.

– Even when the constraint is removed, the material remains deformed

Types of Material Deformation

• Fracture:– The constraint is so intense that it breaks

the material

What to consider?• What are the stresses/external forces the

material will undergo? (Constraints)

• How do we want the material to react to such stresses? (Deformation)

• How will the material react? (Material properties)

• Will the material last a long time? (Degradation)

Degradation

How will a material age?

Degradation• The degradation of a material is the

decline in some of its properties due to its environment or time

Types of Materials

1. Wood• Wood is a ligneous (fibrous) material whose bark has

been removed.

• The mechanical properties differ depending on the type of wood

• Types of wood– Hardwood (deciduous trees)

• More resistant to wear and harder than softwood

– Softwood (coniferous trees)– Modified Wood (properties usually more constant)

• Properties:– Hardness, elasticity, resilience– Low thermal and electric conductivity– Easily shaped and assembled– Light weight

• Issues:– It can rot, be subject to disease– Properties depend on water content and conditions of

growth– Due to its organic nature, fungus, insects and micro-

organisms can infest the wood.

• Protection:– By varnishing, heating, painting or treating the wood,

we can extend its lifetime.

2. Ceramics

• Ceramic is a solid non-metallic material obtained by heating inorganic matter containing various compounds

• Types of ceramic– Crystalline– Non-crystalline (glass)

• Properties– Low thermal and electrical conductivity– Hardness– Resist corrosion– Durable

• Issues– Fragile to shocks and thermal shocks– Wears easily in presence of acids and bases

3. Metals• Metals:

– A material extracted from a mineral ore

• Metals are not usually used in their pure form, but are combined with other substances to improve their properties.

• This mixture is called an alloy (homogeneous mixture of two or more metals)

• Properties (vary on the metal used)– Usually shiny

– Good conductors (heat and electricity)

– Ductility and Malleability depend on the materials

• Degradation– Corrosion and Oxidation

• Protection:– Coat the metal with a less corrosive metal (Zn, Au, Ag,

Ni)– Coat the metal with paint, enamel, grease, resin