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Materials

Force-extension graphs, elastic and plastic deformation

  • 1 thing to know
  • Papers 2 and 3

Overview

Recall questions on the limit of proportionality and the elastic limit, elastic against plastic deformation, the yield point, and loading and unloading curves.

What you need to know

Answer each one before you reveal it.

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What does the gradient of a force-extension graph give, what shape is it for a spring obeying Hooke's law, and what is elastic deformation?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What does the gradient of the straight-line part of a force-extension graph represent?

    Model answer

    It gives the stiffness k of the sample, since ΔF = kΔx.

  2. 2

    What does the force-extension graph of a spring obeying Hooke's law look like?

    Model answer

    It is a straight line passing through the origin.

  3. 3

    What is meant by the limit of proportionality?

    Model answer

    It is the point beyond which the extension is no longer directly proportional to the applied force, so the graph ceases to be a straight line.

  4. 4

    What is meant by the elastic limit?

    Model answer

    It is the maximum load a sample can carry and still return to its original length when the load is removed.

  5. 5

    How are the limit of proportionality and the elastic limit related on a force-extension graph?

    Model answer

    The elastic limit lies at or just beyond the limit of proportionality, so a material can behave elastically for a short way past the point where the graph stops being straight.

  6. 6

    What is meant by elastic deformation?

    Model answer

    The sample returns completely to its original shape and dimensions when the deforming force is removed.

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