Mechanical Engineering: Creep Failure and Design Against Creep
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Questions and Answers

What is the main purpose of a creep test?

  • To apply a constant tensile stress to a specimen at a constant temperature and measure strain over time (correct)
  • To apply a constant tensile stress to a specimen at varying temperatures
  • To measure the rupture lifetime of the material at varying stress levels and temperatures
  • To measure strain as a function of time at varying stress levels and temperatures

    • What is one of the mechanisms of creep mentioned in the text?

  • Thermal activation of dislocations due to melting temperatures
  • Increasing pressure causing strain on the material
  • Vacancies migrating within the material (correct)
  • Plastic deformation of the material at high temperatures

    • Why are materials with high melting temperatures often selected for turbine engine blades?

  • To reduce the susceptibility to creep deformation at high temperatures (correct)
  • To ensure the blades remain ductile under high pressure steam
  • To prevent the formation of voids and material defects
  • To increase the strain rate of the material

    • What is a characteristic of ceramics that provides resistance to deformation by creep?

    <p>High melting temperatures</p> Signup and view all the answers

    What is an example application where components experience creep phenomenon?

    <p>Gas turbine engines</p> Signup and view all the answers

    What type of stress do power plant pipes and turbine engine blades experience?

    <p>Centrifugal stresses and high pressure steam lines</p> Signup and view all the answers

    Why is it important to know the operating conditions of the system when selecting materials for an application?

    <p>Materials experience thermally activated creep at different temperatures</p> Signup and view all the answers

    Which temperature range can polymers or tin-lead solder be susceptible to creep?

    <p>$30˚C$</p> Signup and view all the answers

    What factor determines the rupture lifetime in a creep test?

    <p>The slope of the strain vs. time curve</p> Signup and view all the answers

    What is being measured in a typical creep test?

    <p>Strain as a function of time at a constant stress and temperature</p> Signup and view all the answers

    What is creep in the context of materials science?

    <p>Time-dependent deformation of a material under constant stress</p> Signup and view all the answers

    At what temperature does creep become significant for a material?

    <p>0.4 Tm</p> Signup and view all the answers

    What is one possible consequence of creep failure?

    <p>Fracture known as stress rupture</p> Signup and view all the answers

    How does creep occur in the context of creep mechanisms?

    <p>Via atomic diffusion and elongation of grains</p> Signup and view all the answers

    What renders a material useless in performing its intended function in the context of creep failure?

    <p>Dimensional change</p> Signup and view all the answers

    When does creep failure occur?

    <p>When stress is less than the yield stress</p> Signup and view all the answers

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