Materials Flashcards
What is density?
A measure of how much mass an object has per unit of volume
When might a high density be needed?
When trying to strengthen things such as buildings
When might a low density be needed?
When trying to lighten things or insulate them such as air balloons or foam packaging
What is an alloy?
It is a mixture of a metal with other elements to help improve its properties
Why are alloys created?
To make metals stronger, harder, more resistant to corrosion, or to change their appearence
What is Hooke’s law?
It states that the extension of a spring is directly proportional to the force being applied, as long as the elastic limit is not exceeded
What does a large spring constant mean?
It means the spring is stiff, so a large force is required to produce a small extension
How do springs add up in series?
1/Ktotal = 1/K1 + 1/K2+…
How do springs add up in parallel?
Ktotal = K1 + K2 +…
What is tensile stress?
The force applied per unit of cross-sectional area of a material (measured in N/m^2 or Pa)
What is tensile strain?
The extension/change in length divided by the original length (it has no units)
Describe material that has a large stress and a small strain
It requires a large force for a small extension, so the material is strong and stiff
Describe a material that has a large strain and a small stress
It requires a small force for a large extension, so the material is flexible and ductile
What is elastic strain energy?
The energy stored in a material (like a spring) when it is stretched or compressed, as long as it stays within the elastic limit
What does the area under a force-extension graph show?
Elastic strain energy per unit volume
What is meant by elastic limit?
The point beyond which the material will no longer return to its original shape once the force is removed, this means permanent deformation begins
What is plastic behaviour?
When a material permanently deform after a force is applied it enters a plastic region where it no longer returns to its original shape
What is the yeild point?
The point where a material suddenly stretches with little or no extra force (after this point plastic deformation happens easily)
What is necking?
When a material under tension starts to narrow at a specific point just before it breaks
What is ultimate tensile stress (UTS)?
The maximum stress that a material can withstand before necking begins (the maximum stress a material can withstand)
What is breaking stress?
The stress at which a material finally breaks and separates into two peices (fractures)
What does it mean for a material to be brittle?
The material breaks or fractures with little plastic deformation (it doesn’t stretch much before it breaks)
e.g. glass, chocolate and ceramics
Draw a stress-strain graph for a brittle material
Look in booklet for answer
What does it mean for a material to be ductile?
The material can undergo significant plastic deformation before breaking or fracturing (it stretches quite a bit before breaking)
e.g. copper, steel and aluminium
Draw a stress-strain graph for a ductile material
Look in booklet for answer
What is meant by the Young modulus of a material?
A measure of the stiffness of a material (the ratio of tensile stress to tensile strain)
What is the significance of the gradient of a stress-strain graph?
It tells you the Young modulus of the material
How is energy conserved during the stretching or compressing of a material?
When a spring is stretched work is done on the spring, if the spring is stretched within its elastic limit then the energy is stored by the spring but if it is stretched past its elastic limit then some energy is stored and some is lost (due to heat)
What is the significance of the area under a stress-strain graph?
It shows you the elastic strain energy stored per unit volume
How is spring energy transformed into kinetic energy?
When a spring is stretched or compressed, the stored elastic strain energy is conserved into kinetic energy as the spring starts to move up and down
How is spring energy transformed into gravitational potential energy?
If a spring pushes an object upwards , the elastic strain energy is partly converted into gravitational potential energy as the spring gains height
What conservation laws apply when spring energy is transformed?
Energy conservation still applies the total energy remains constant, the spring energy is transferred to other forms (KE and GPE)
What is the role of energy conservation in ethical transport design ?
Ethical transport design aims to reduce waste energy to protect the environment, save resources and benefit society
