Properties of Materials Flashcards
What does toughness mean and what do materials require to be tough?
This is the amount of energy needed per square meter to create a greater surface area or absorbed per cubic meter to apply stress to the material.
Tough materials cannot have passing cracks, must experience lots of plastic deformation before breaking, and need lots of energy to break.
This is J/m^2 or J/m^3
Brittle materials easily have cracks pass through and deform quickly so they shatter, (i.e. - ceramics).
What is elastic deformation?
This is where a temporary change is created when stress is applied to an object. No loss of energy.
What is plastic deformation?
Permanent change is created when stress is applied to an object. No loss of energy.
What is strength? What’s it measured in?
This is the maximum stress an object can withstand before failure.
Measured in Pa, (pascals).
What is stress? What types are there?
Stress is measured in Pascals with the sigma sign, σ, and is the force applied divided by the surface area. This can be compressive, tension, (stretching), or torsion, (twisting).
What is a malleable object?
This is an object that can be hammered or rolled into a sheet as a permanent response to a compressive force.
What is a ductile object?
This is an object that can be drawn into fibres as a response to a tensile force.
What is hardness, and what is it measured in?
Hardness is how good a material resists scratching and dents, and is measured in Pa, pascals.
Describe metals, (one class of materials)?
- Pure metals are soft meaning they dent easily and they are less stiff so require less stress, such as tensile stress, to be drawn into fibres.
- Lead can be moulded by hand.
- Gold and copper can be hammered into shape, malleable.
- Metals are ductile so they can be drawn into fibres.
- Metal alloys such as steel are more tough and stronger, they require a greater force and experience more plastic deformation before breaking.
- Metals are malleable.
Describe ceramics?
These are hard and resist scratching.
They’re brittle, not much energy is needed per square meter to shatter them.
They are stiff - difficult to shape.
Ceramics can include pottery, china, and engineering ceramics such as silicon carbide and alumina.
Describe polymers?
These are natural, (leather and cotton), or synthetic, (polythene).
Glassy polymers have similar properties to glasses and as they are superior they are used as lenses.
Semi-crystalline polymers are tough so require more energy and deformation to break.
What should be considered when choosing materials?
Mechanical properties.
Cost.
Appearance.
