Materials Flashcards
What is the density of water?
1g cm^-3
What is hooked law?
Force is proportional to extension
What are the units of K?
Nm^-1
What happens to k if springs are in parallel/series?
Parallel = k halves Series = k doubles
When is stress positive or negative?
Tensile = positive Compressive = negative
At what point does hookes law no longer apply?
Limit of proportionality (line no longer straight)
What is the gradient on force extension graph?
K
What happens at the elastic limit?
Plastic deformation (permanent extension)
What happens in plastic deformation?
- Work done to separate atoms
- energy not stored as strain
- lost as heat
What in elastic stuff?
- Energy stored as elastic strain energy
- when force is removed, energy is released
Change is kinetic = change in potential
What is area under stress strain graph?
Energy stored per unit volume
Learn force against extension graph for an elastic stretch
Have fun
What structure do brittle materials have?
Crystalline or polycrystalline
Describe brittle materials
- have strong bonds = rigid and stiff
- when stress applied = cracks on surface get bigger until its snaps
Describe what happens when stress applied to a metal
Atoms move to prevent cracks getting bigger and so aren’t brittle
What do force against extension graphs depend on?
Materials dimensions
Stress against strain graphs
Independent of dimensions (same for that material even if different dimensions)
What is the yield point?
Point at which material stretches without extra load (lots of plastic deformation with reduced load)
Derive energy stored from f-l graph
Area of a triangle and that
What is elastic strain energy?
The work done stretching a material (its stored as potential)
- it’s the area under f-l graph
Why doesn’t strain have units?
It’s a ratio
Crumple zones?
Modern cars have areas called crumple zones so that the kinetic energy goes to changing shape rather than into the passengers (public transport have to balance these with safety of driver)
(Stretched over elastic limit) why is the unloading line on force against extension graph parallel ?
The Ks are the same (area between loading and unloading = work done to permanently deform the wire)
What are the units of Young’s modulus and stress?
Nm^-2 or Pa
