Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages Brittle Fracture Questions
Brittle Fracture AimsBefore you startIntroductionWhen do atomic bonds break?Why do cracks weaken a material?Inglis and the crack tip stress ideaCan we calculate the energy changes?What about tension?Another way of expressing the energiesAnother way of calculating the energiesWhy bother if they are the same?Coping with a scatter in strengthSimulation of Weibull modulus experimentWhen does the sample fail completely?Sub-critical crack growth and R-curvesSummaryQuestionsGoing further
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Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

  1. The Lennard-Jones potential best describes which of the following:

    a The energy required to break a typical metal
    b How flaws affect the energy of a lattice
    c The energy associated with stretching an atom

  2. Which of the following situations is required for fast fracture to occur?

    a The crack tip is sufficiently sharp
    b dG/dc is greater than dR/dc
    c The applied stress is near the ultimate tensile strength of the material
    d The strain energy release rate G is equal to the fracture energy R.

  3. In the wedging setup, which of the following will *not* influence the critical crack length?

    a The position of the wedge
    b The stiffness of the material
    c The thickness of the peeling layer
    d The surface energy of the material

  4. Which one of Irwin's modes of fracture best describes a car tyre skidding on a dry road?

    a Mode I
    b Mode II
    c Mode III

  5. What is the critical stress intensity factor equal to when no residual stresses are present?

    a Fracture toughness
    b Crack resistance
    c Ultimate tensile strength
    d Fracture energy

  6. What best describes the situation in wedging?

    a As the wedge position is varied, it is always energetically favourable for the crack to return to an equilibrium length
    b The fracture energy dominates at small crack lengths
    c If the crack becomes very long in comparison to the geometry of the setup, unstable fast fracture may occur

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