Edexcel A-Level Physics 9PH0
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Materials
Stress-strain graphs, ductile and brittle materials
- 1 thing to know
- Papers 2 and 3
Overview
Recall questions on the shape of a ductile metal's graph, breaking stress, what the gradient gives, and how a brittle material differs.
What you need to know
Answer each one before you reveal it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What does the area enclosed between the loading and unloading curves represent?
Model answer
It represents the energy per cycle that is not recovered but is dissipated within the material, mainly as thermal energy.
- 2
How does a force-compression graph for a spring compare with its force-extension graph?
Model answer
It shows the same straight-line proportional behaviour and the same stiffness at small compressions, but the line ends abruptly once the coils touch and the spring can be compressed no further.
- 3
What is the shape of the stress-strain graph for a ductile metal such as copper?
Model answer
It is a straight line up to the limit of proportionality, then curves over at the yield point, extends by a large plastic strain with little extra stress, and finally fractures.
- 4
What is meant by breaking stress?
Model answer
It is the stress at which the material actually fractures.
- 5
What does the gradient of the straight-line region of a stress-strain graph give?
Model answer
It gives the Young modulus of the material.
- 6
Why is a stress-strain graph more useful than a force-extension graph when comparing two materials?
Model answer
Stress and strain do not depend on the dimensions of the sample tested, so the graph describes the material itself rather than one particular specimen.
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