Materials Flashcards
(32 cards)
Define density
Mass per unit volume
Define hooke’s law
Extension is directly proportional to the force applies, given that environmental conditions are kept constant
Define the limit of proportionality
The point after which hooke’s law is no longer obeyed
Define the elastic limit
Point at which any more force applies will cause material to deform plastically (permanently stretched)
Give the equations for hooke’s law
F = k L
- K is the spring constant
- L is the extension
Define spring constant
How stiff a spring is
Define tensile stress
The force per unit cross-sectional area
Define tensile strain
The extension over original length (caused by stress)
Give the equation for tensile stress
F/A
Give the equation for tensile strain
Extension / original length
What does the area under a force extension graph represent
The elastic strain energy
Define elastic strain energy
The work done to compress / stretch a material
Give the equation for elastic strain energy
1/2 F x L
Define breaking stress
The value of stress at which the material breaks apart
If a material has plastic properties, what does this mean
It’s will experience a large amount of extension as the force is increased
If a material is brittle, what does this mean
The material will experience little extension, so likely to break apart
Why on a force - extension graph des the unloading line not return to the origin
It has been stretched beyond its elastic limit
Why on a force extension graph are the loading and unloading lines parallel
The stiffness of the material stays constant
On a force extension graph, what does the area between the loading and unloading lines represent
The work done to permanently deform the material
What are the energy stores when a material is stretched elastically
All work done is stored as elastic strain energy
What does elastic mean
Material returns to original shape
What does plastic mean
Material doesn’t return back to its original shape
What are the energy transfers when a material stretched plastically
Energy is dissipated as heat
How do seat belts work
Stretch so some of cars KE is transferred to elastic strain energy
