Properties of materials and structures Flashcards
What is the equation for stress?
stress = force/cross-sectional area
What are the units for stress?
N m*-2 / Pa
What is the equation for strain?
change in length/ original length
What are the units for strain?
no units - ratio
What is the relationship between change in length and the original length of the material?
they change in proportionality to each other
i.e. a bar twice as long stretches twice as much
What is the proportional limit?
the end point of the stress-strain curve where the relationship is linear
What is the elastic limit?
the greatest stress that can be applied to a material so that when the stress is removed, it will return to its original shape.
What is elastic behaviour?
a material which exhibits elastic behaviour will deform instantly and return to its original shape as soon as the load is removed
What is plastic behaviour?
a material which exhibits plastic behaviour will deform instantly and when the load is removed, it will retain its new shape
what is the yield point?
the point which once passed, the material will undergo considerable elongation without a corresponding increase in stress
What is the stress at the yield point known as?
the yield stress
What happens during strain hardening?
the material undergoes changes in its atomic and crystalline structure resulting in an increased resistance to further deformation
What is the ultimate strength?
the highest point on the curve after which stretching occurs and necking or waisting of the material occurs whereby the cross-sectional area is reduced
What is the rupture point?
is the point at which the material breaks
Describe a brittle material
a material that can only survive a limited strain before breaking - e.g. glass
Describe a ductile material
a material that deforms plastically before breaking e.g. copper
Describe the differences between a brittle and ductile material
a brittle material only requires a small strain before breaking
a ductile material behaves plastically before breaking
Describe the phenomenon of necking
after the ultimate strength point is passed, the material stretches and its cross-sectional area is reduced.
What does the Young’s Modulus of a material indicate?
stiffness - how difficult a material is to deform under loading
What is stiffness?
a measure of how difficult a material is to deform under loading
What is the formula for Young’s Modulus?
stress/strain
What are the units for Young’s Modulus?
Pa
Describe a material with a small young’s modulus
such a material requires only a small amount of stress to produce a large strain (flexible)
Give an example of a material with a small youngs modulus
rubber
Describe a material with a large Young’s Modulus
such a material requires a large stress to produce even a small strain (stiff)
Give an example of a material with a large YM
diamond
what is rigidity? what is the equation?
A materials ability to resist axial deformation
rigidity = YM x cross-sectional area
thus, rigidity increases with cross-sectional area
Measured in Newtons
What is stiffness?
the force required to produce a unit deflection
What is the equation for stiffness?
k = EA/change in length
What is the opposite of stiffness? What does it mean?
Flexibility - deflection under a unit load
