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
