Materials Flashcards
what is the density of a material
mass per unit volume
what is hookes law
the extension is directly proportional to the force applied given that the environmental conditions are kept constant
what is the limit of proportionality
is the point after hookes law is no longer obeyed
what is the elastic limit
is when beyond this if you apply any more forces the object becomes plastically deformed
what does the spring constant measure
the stiffness of the string
what is tensile stress
force applied per unit cross sectional area
what is tensile strain
this is the extension over the original length
what is the energy stored as when work is done on a material to stretch or compress it
elastic strain energy
what is breaking stress
is the value of stress at which the material will brak apart
what can force-extension graphs show
the properties of a specific object
what are the two main behaviors that a material can exhibit on a force-extension graph
plastic and brittle
what is plastic behavior
this is where a material will experience a large amount of extension as the load is increased, especially beyond the elastic limit
what is brittle behavior
this is where a material will extend very little, and therefore is likely to fracture at a low extension
once a material is stretched beyond its elastic limit what will it show on a force extension graph
the unloading line will not return to the origin , however the loading and unloading lines will be parallel because the materials stiffness is constant
what is the area between the loading and unloading line equal to
the work done to permanently deform the material
when a stretch is elastic what is all the work done stored as
elastic strain energy
what does elastic mean
a material will return to its original shape once the force applied is removed
when a stretch is plastic work is done to do what and so what happens to the energy
to move the atoms apart and so the energy is dissipated as heat
how is this fact used when designing safety features for cars
- work is done to deform crumple zones plastically to decrease the cars kinetic energy
- seat belts stretch in order to covert some of the passengers kinetic energy into elastic strain energy
when a spring is hung vertically and stretched and then the force is removed what happens to the energy at different stages
- kinetic energy is converted into elastic strain energy when the spring is stretched
- when the force is removed the elastic stain energy will be transferred back to kinetic energy this kinetic energy is then transferred to gravitational potential energy
what do stress-strain graphs describe
they describe the behavior of a material
what is the ultimate tensile stress
the highest point on the gaph as it shows the maximum stress the material can withstand
what can the shape of the line of a stress-strain show
whether the material is ductile, brittle or plastic
what is ductile
can undergo a large amount of plastic deformation before fracturing
