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