materials Flashcards
stiff
high ym - strong because it can take a lot of stress fir little strain
brittle
no plastic region
tough
it permantely deforms to withstand stress
ductile
lots of strain for little stress - does not need a lot of force
hookes law
the force needed to stretch a string is directly proportional to the extension of the string
what is k and what does it mean if it is high
spring constant and stiffer spring
series (effective spring constant)
k = (1/k + 1/k)^-1 (like parallel resistors)
in series do both springs feel each mass equally
yes
overall spring constant (series)
less than each k in each spring (multiply by both extension)
parallel (effective spring constant)
k = k1 + k2
in parallel do both springs feel each mass equally
no, the weight is shared by the 2 sprigs
overall spring constant (parallel)
overall k is bigger than k in each spring (multiple by 1 extension)
hysterisis
-the energy stored in loading is greater than the energy released in unloading
-permanently plastically deforms bonds in the material
-goes back to og length and shape
-eg) rubber
compressive forces
squeeze and object and reduce its size
tensile forces
act to pull or stretch an object
stiff
resists deformation
ceramic
tough
resists breaking, even after deforming
aluminum
strong
resists deformation and breaking
steel
ductile
deforms before it breaks
gold
brittle
breaks before it deforms
glass
hard
resists dents, scratches and other permanent changes under compressive forces
iron
elastic
deforms but returns to og state
plastic
does not return to og state
what happens if you keep stretching an elastic material
the bonds between the atoms are stretched and when this breaks, it has reached its yield point
limit of proportionality
in this region the extension is proportional to the force applied
elastic limit
up until this point, the material will return to its initial shape/size when the force is removed
yield point (just before a peak on graph)
-when the load is increased beyond this point, the material behaves plastically
- a small increase in load causes a very large increase in extension and the material remains extended once the fore has been removed
breaking point
the load will break the material
stress
how much force is affecting the cross sectional area
strain
ratio between extension and og length
what should you do if strain is in a percentage
make it into a fraction
if a material is stiff, what does this mean about the strain and ym
smaller the strain = bigger the ym
what do you compare using the gradient of a stress- strain graph
stiffness
