3.4 Materials Flashcards
Tensile force
A force produces an extension of the object.
Compressive force
A force that reduces the length of an object
Hooke’s Law
Force is proportional to extension so long as the elastic limit is not exceeded.
Elastic deformation
When an object will return to its original shape when the load is removed.
Plastic deformation
A permanent change in shape that remains once the load is removed
What is k in F = kx
The force constant
What are the units of force constant (k)
Nm^-1
What is represented by the area under a force- extension graph?
The work done by stretching the object
What is meant by an elastic material?
A material which can be significantly deformed and will return to it’s original shape
Tensile stress
The force applied per unit cross sectional area.
Tensile strain
The fractional change in length of an object
What is a ductile material
A material which can be drawn into a wire of hammered into thin sheets
What is the limit of proportionality in a material?
The point at which a material stops obeying Hooke’s Law
What is the elastic limit of a material?
The point at which a material starts to plastically deform
What is the yield point of a material?
The point at which the material starts to extend rapidly as stress increases
What is the ultimate tensile strength of a material?
The maximum stress a material can withstand before breaking
What is the breaking strength of a material?
The stress at the point of fracture
What is a strong material?
One with a high ultimate tensile strength
What are the units of Young Modulus?
Pa OR Nm^−2
When does the Young Modulus apply to a material?
When stress is proportional to strain OR when it is obeying Hooke’s law
How do you find the Young Modulus from a stress- strain graph?
The gradient of the initial straight line region.
What material property does Young Modulus measure?
The stiffness
What is a brittle material?
A material the show only elastic behaviour up to its breaking point, without plastically deforming.
What is a polymeric material?
A material made from long chain molecules.
