Materials Flashcards
What is density?
the mass per unit volume of an object
What is the equation to calculate density? Include units
P=m/v
where:
p= density (kgm^-3)
m= mass (kg)
v= volume (m^3)
What does Hooke’s law state?
the extension of the material is directly proportional to the applied force (load) up to the limit of proportionality
What is the equation for Hooke’s law?
F = kΔL
where:
F = force (N)
k = spring constant (N m^–1)
ΔL = extension (m)
What is the spring constant? What does it measure?
-a property of the material being stretched
-measures the stiffness of a material
What do we mean by the natural length?
the original length of a spring
Draw the Hooke’s law graph, label all areas
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/Force-Extension-Graph.png
What do we mean by the limit or proportionality?
the point beyond which Hooke’s law is no longer true when stretching a material
What do we mean by the elastic limit?
the maximum amount a material can be stretched and still return to its original length
What is the area under a force-extension graph?
the work done to extend a spring
or
elastic potential energy store
How do we combine spring constants in parallel?
kTotal= k1 + k2 +k3…
How do we combine spring constants in series?
1/kTotal= 1/k1 + 1/k2 +1/k3…..
What does elastic behaviour mean?
regains shape after deformation
What does plastic behaviour mean?
permanently deformed after extension
- doesn’t return to original length once load is removed
What is tensile stress?
the force exerted per unit cross-sectional area of a material
How can we work out tensile stress?
σ= F/A
where:
σ = tensile stress (Pa)
F = force applied (N)
A = cross-sectional area (m^2)
What is tensile strain?
extension per unit length
What do we mean by the ultimate tensile stress?
the maximum force per original cross-sectional area a wire is able to support until it breaks
How can we work out tensile strain?
tensile strain= ΔL/L
where:
ΔL = extension (m)
L = original length (m)
What is the area under stress-strain graph?
work done/volume
What is yield stress?
the stress at which the material extends plastically when no or a small amount is added
What is braking point?
-this is the maximum stress a material can stand before it breaks
What do we mean by elastic region?
the region of the graph up till the elastic limit
-in this region, the material will return to its original shape when the applied force is removed
What do we mean by plastic reigon?
the region of the graph after the elastic limit
-in this region, the material has deformed permanently and will not return to its original shape when the applied force is removed
Draw a stress-strain graph labelling all areas
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/Stress-Strain-Graph.png
What does it mean when a material is brittle?
very little to no plastic region
-the material breaks with little elastic and insignificant plastic deformation
What does it mean when a material is ductile?
larger plastic region e.g. rubber, copper
-the material stretches into a new shape before breaking
Draw and label the graph for loading and unloading a wire against force and extension
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/4.7.6-Loading-and-unloading-graph-1.png
Draw and label the graph for loading and unloading a rubber band against force and extension
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/4.7.6-Loading-and-unloading-graph-2.png
What do we mean by elastic (young’s) modulus?
a measure of stiffness
-material dependant
How can we work out the young’s modulus of a material?
tensile stress/ tensile strain
or
(force x natural length)/(cross-sectional area x extension)
where:
F = force (N)
L = original length (m)
A = cross-sectional area (m^2)
ΔL = extension (m)
Young’s modulus (Pa)
How can we calculate the young modulus from a stress-strain graph?
work out the gradient
RP4: describe this practical
-aim of the experiment is to measure the young modulus of a metal in the form of a wire
-this requires a clamped horizontal wire over a pulley
- can also be done with a vertical wire attached to the ceiling with a mass attached
RP4: How do you work out the young modulus from the measurements?
-if you have stress and strain, plot the graph and find the gradient
-if you have all values e.g. F, A, L etc., plot a graph of force against extension and multiply the gradient by natural length/ cross-sectional area
What is the area of a stress-strain graph?
work done per unit volume
