materials Flashcards
what is deformation
We can apply stretching, compressing or twisting forces to an object that will result in it changing shape.
what is plastic deformation
normally An elastic object will return to its original position once forces have been removed however if it experiences plastic deformation (reached its elastic limit) it will no longer be able to do this .
(permanent deformation )
what is elastic limit ?
where an elastic object will either break or experience plastic deformation.
(can no longer go back to its original position without a force acting on it)
Brittleness
how much it will shatter or crack when subjected to a shock.
Strength
how much breaking stress it can withstand.
Malleability
how easily it can be formed into thin sheets.
Ductility
how easily it can be drawn into a wire.
what is the unit for Force, F
N newtons
what is the unit for spring constant, K
Newtons per meter , N/m
or Nm-1
what is the unit for change in extension , Δx
Meters m
what is hooke’s law ?
hooke’s law states that the relationship between force and extension is directly proportional
what is the equation for hooke’s law ?
force= spring constant x extension
what is the symbol for elastic energy (youngs modulus)
ΔE
what is the unit for stress
Nm-2
what is the unit for strain
there isn’t a unit
what is the unit for young’s modulus ?
Nm-2
what is the unit for cross section ?
m2
what is the unit for length
m
definition of stress
Stress is a measure of the force acting within a material.
definition of strain
Strain is the extension of the material compared to its original length. This is the result of stress.
definition of the young’s modulus
The Young modulus is a constant of proportionality that shows the stiffness of the material.
what is the elastic region on a Stress strain curve?
the section before an object reaches its elastic limit
what happens to the object in the elastic region?
- the bonds between atoms increase in length due to the forces acting on them, if the force is removed then they return to their original shape (equilibrium positions)
what is the plastic region?
beyond the elastic limit
what happens in the plastic region?
- the arrangement of atoms changes
- the object experiences plastic deformation
- the object may contract however it will not revert to its equilibrium position
Creep
when materials under stress deform gradually over time. This is more severe for materials that have been subject to high heats for a long period of time.
fatigue
the embrittlement and failure of a material that occurs with relatively low levels of stress, if these are repeatedly applied and relaxed over many cycles
what does dissipated mean?
lost to surroundings
what is elastic hysteresis?
some materials require more energy to load the material with stress than they do for unloading it (the energy is unequal). Energy is therefore dissipated into the surroundings as heat when unloading, which is why there is a difference.
on a stress-strain graph what will the line look like for a material with a high young’s modulus ?
it will be a steep line (stiffness)
how with the line look on a stress-strain graph if the material is brittle?
- the line will be very short after the elastic limit
density
os the mass per unit volume
density in solids and liquids is considered ….
fixed
g to kg=
divided by 1000
mg to g
divided by 1000
mg to kg
divided by 1000 then divided by 1000 again
volume =(cube)
hight x width x length
volume = (sphear)
4/3 x π x r3
unit for volume =
m3
unit for density
kgm-3
density equation
density = m divided by v (m=kg, v= m-3)
laminar flow
streamlines that move in straight lines (or curved but e=with a constant distance between) and do not cross each other
turbulent flow
streamlines that do cross each other and create vortices and eddy current.
what is drag?
objects that experience lots of turbulant flow, experience drag
e.g a tractor experiences more drag than a racing car.
how can objects be designed to experience less drag?
they can be designed to be more streamline e.g flat, sleek curves
streamlined objects are more…
aerodynamic and are able to move quicker because they experience less drag
what is viscosity
viscosity is a quantity that describes a fluids resistant flow
a viscous fluid =
thicker less flowing fluid e.g honey
is water viscus ?
no
if you heat up a gas the viscosity will…
increase
if you heat up a liquid the viscosity will…
decrease
on a bike chain what kind of lubrixate should be used ?
a very viscous lubricate should be used e.g oil (wd40) .. as this is very viscous it will create a barrier between the chain and the cog so they do not catch on each other and cause any damage.
definition of elastic
an object that will return to its original position once these stretching/ compressing forces have been removed.
definition of inelastic
an object that will not return to its original position once stretching/ compressing forces have been removed
(stress strain curves)
strong objects, their elastic limit will be…
at a higher stress (higher up the graph)
(stress strain curves)
brittle objects break under very little strain , very little plastic deformation so their breaking point will be …
not very far across the graph
ductile objects experience alot of plastic deformation , they break under alot of strain so their breaking point will be …
very far across the graph
