Materials Flashcards
(33 cards)
What is the formula for density?
Density = mass/volume
ρ = m/v
Measured in kg m3
What is Hookes Law?
The force needed to stretch a material is directly proportional to the extension up to the limit of proportionality
F = kΔL
Where does Hookes law apply?
- up to the limit of proportionality
- by springs and metal wires - not really by things like plastics, composites, ceramics, etc.
- also where there is compression - ΔL is where the spring gets shorter
What is the spring constant?
- aka stiffness
- measured in Nm-1
- how much is required to extend the spring by 1m
What is elastic deformation?
Material returns to it’s original shape when forces on it are removed
What is plastic deformation?
Material is permanently deformed - does not return to original size and shape once forces on it are removed
What is the limit of proportionality?
The largest extension at which Hookes Law is obeyed
What is the elastic limit?
The largest extension in which deformation is still elastic - beyond this it becomes permanently deformed
What is permanent deformation?
A change in shape of a material that remains after force is removed
Spring constant for springs in series?
1/kt = 1/k1 + 1/k2 + 1/k3 …
(Basically the connecting circuits in parallel)
Spring constant of springs in parallel?
kt = k1 + k2 + k3 …
(Basically connecting circuits in series)
How do you calculate e
How do you calculate energy stored in a stretched material obeying Hookes law using a graph?
It is the area under the line - can be calculated by counting squares
Equation to calculate work done to stretch a material obeying Hookes Law?
W = (FΔL)/2
W = (kΔL^2)/2
(Sub in F = kΔL)
What is a compressive force?
a pair of forces that are acting to squash a material
what is a tensile force?
a pair of forces that are acting to stretch a material
what is an extensive vs intensive property?
- extensive = property depends on the size of an object - eg. mass, force, extension
- intensive = property doesnt depend on size of an object - eg. density, stress, strain
with a loading and unloading curve of a plastically deformed material, what does the area between the 2 curves represent?
the work done to plastically deform the object - work is done to rearrange the atoms in the material and energy is transferred to the thermal energy stores of the material + surroundings
what does the gradient and area of a stress-strain graph represent?
- gradient = the Young’s modulus of the material
- area underneath = work done per unit volume
what is tensile stress equation?
σ = F/A
where:
σ = stress (Pa)
F = force (N)
A = cross sectional area (m2)
what is the equation for tensile strain?
ε = ΔL/L
where:
ε = strain (unitless)
ΔL = change in length/ extension (m)
L = original length (m)
on a stress strain graph, what is yield point 1?
stress at which material weakens and stretches plastically without additional force
on a stress-strain graph, what is yield point 2?
stress at which material undergoes plastic flow - small stress leads to large strain because CSA of material is decreasing rapidly
on a stress-strain graph, what is the ultimate tensile stress?
the maximum stress the material experiences - a measure of the material’s strength
