unit 1 materials Flashcards
Density
Mass per unit volume
ρ = m/V
Upthrust
due to different pressure exerted on surface of object
Archimedes law
upthrust = weight off displaced volume
= ρVg
Stokes Law
F = 6πηrv
viscous drag force under assumption: small, spherical, laminar, slow
laminar flow
smooth paths, little to no mixing between adjacent layers of fluid
turbulent
mixing between layers and form separate currents
viscosity
how resistant a fluid is to deformation
determined by internal frictional forces
relationship of viscosity and temp
η is temperature dependent
-liquids: T ↑ η ↓
-gases: T ↑ η ↑
hookes law
Extension is directly proportional to force until the spring reaches it’s elastic limit
-ΔF = kΔx
(F: external force, k: stiffness(spring constant), Δx: extension)
stress
force per unit cross sectional area
unit: Pa (N/m²)
strain
change in length over original length
unit: dimensionless
Young Modulus
value that describes stiffness of material (ratio of stress applied and resulting deformation)
-E=σ/ε=(F/A)/(Δx/L)
Limit of proportionality
The limit beyond which, when a wire or spring is stretched, its extension is no longer proportional to the force that stretches it.
Elastic limit
Maximum stress that a material will withstand without plastic deformation.
yield point
point where materials begins to rapidly extend without additional stress.
elastic deformation
material returns to original shape once applied force is removed
all work is stored as elastic strain energy
plastic deformation
materials shape is changed permanently
some work is also dissipated as heat
elastic strain energy
area under: force-extension graph
ΔE = 0.5kΔx² = 0.5FΔx
unit: J
ductile
can undergo large plastic deformation before breaking/
look for: max x value
brittle (brittleness)
extend very little: likely to fracture at low strain
look for: min x value
strong (strength)
requires large force/stress to break
look for: max y (high UTS)
tough (toughness)
can withstand repeated deformation
look for: max area under curve
elastic (elasticity)
non-permanent deformation, bonds are stretched but not torn apart
stiff (stiffness)
how resistant a material is to elastic deformation (Young modulus)
look for: slope (linear)
hard
doesn’t scratch easily
durable
can be repeatedly loaded/unloaded without change in properties
