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

What is creep in materials?

  • Time-dependent deformation under constant stress (correct)
  • Permanent dimensional change without any stress
  • Temperature-dependent deformation under varying stress
  • Non-permanent dimensional change under constant stress

    • When does creep become significant for a material?

  • When the temperature is less than 0.4 Tm
  • When the stress is greater than the yield stress
  • When the temperature is greater than 0.4 Tm (correct)
  • When the stress is less than the yield stress

    • What type of process leads to creep in materials?

  • Diffusion-controlled process (correct)
  • Mechanical deformation process
  • Pressure-driven process
  • Heat-induced process

    • What renders a material useless in performing its intended function in creep failure?

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

    What can result from sufficient strain or creep in materials?

    <p>Stress rupture or creep fracture</p> Signup and view all the answers

    In what direction do atoms move in response to the applied stress and temperature during creep?

    <p>To fill the voids in the grains, resulting in elongation of the grain</p> Signup and view all the answers

    What is the main mechanism of creep deformation mentioned in the text?

    <p>Vacancy migration along grain boundaries</p> Signup and view all the answers

    Which components are cited in the text as examples experiencing creep phenomenon?

    <p>Boilers, gas turbine engines, and ovens</p> Signup and view all the answers

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

    <p>To withstand sustained stress over time at a relatively high temperature</p> Signup and view all the answers

    What is the purpose of a creep test mentioned in the text?

    <p>To measure strain over a period of time at a constant stress and temperature</p> Signup and view all the answers

    Why are nickel-based superalloys mentioned as susceptible to creep at relatively high temperatures?

    <p>Due to their susceptibility to creep at relatively high temperatures</p> Signup and view all the answers

    What can be inferred about ceramics based on the information provided in the text?

    <p>Ceramics have very high resistance to deformation by creep</p> Signup and view all the answers

    What does the slope of the strain vs. time curve in a creep test represent?

    <p>Strain rate of the material during the test</p> Signup and view all the answers

    Why is it important to know the operating conditions of a system when selecting materials for an application to prevent failure due to creep deformation?

    <p>To understand at what temperature materials experience thermally activated creep</p> Signup and view all the answers

    What is the purpose of materials experiencing a creep test?

    <p>To assess their behavior under constant tensile stress and temperature</p> Signup and view all the answers

    What is an example of an application where components experience centrifugal stresses and high pressure steam lines?

    <p>Turbine engine blades</p> Signup and view all the answers

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