Paper 1- Materials Flashcards
Define density
Mass per unit volume
Define stress
The force per unit area of cross section
Define strain
The extension per unit original length
What is Hooke’s law?
Up to the limit of proportionality, the extension of a wire or spring is proportional to the applied load
Define strength of a material
The maximum force that can be applied to a material without breaking it
Define stiffness of a material
A measure of the difficulty of changing the shape of a material
What does creep mean in terms of materials?
The material continues to extend despite force remaining constant
Give an example of an amorphous material
Glass
What is the area under a stress-strain graph equal to?
The elastic strain energy
What is the Young Modulus?
The constant ratio of stress/ strain, provided the limit of proportionality has not been exceeded
What is a brittle material?
A material which will extend very little so is likely to fracture at a low extension
What is a plastic material?
A material which will experience a very large amount of extension as load is increased, especially beyond elastic limit
What is a ductile material?
A material that will undergo a large amount of plastic deformation before fracturing
Define elastic strain energy
Work done on a material to stretch or compress it
What is the area between loading and unloading lines on a force extension graph equal to?
Work done to permanently deform the material
What is the ultimate tensile stress?
The maximum stress a material can withstand
What is the breaking stress of a material?
The value of stress for which a material will break apart
What is the gradient of a stress-strain graph equal to?
Young’s modulus
What is the difference between a stress-strain and a force-extension graph?
Stress-strain describes the behaviour of a material rather than a specific object
What is Youngs modulus a measure of?
The stiffness of a material
What happens to a material after an elastic stretch?
It returns to its original shape
What happens to work done in an elastic stretch?
It is stored as elastic strain energy
Why do car seatbelts stretch?
To convert some of the passengers kinetic energy into elastic strain energy
What happens to a material after a plastic stretch?
It is permanently deformed
