Materials Spot the difference 1. The Manner in which atoms are chemically bound changes its properties.

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