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

What is creep in the context of material science?

  • Temperature-dependent deformation under varying stress
  • Non-deformation under any stress or temperature
  • Time-dependent deformation under constant stress (correct)
  • Stress-dependent deformation under constant temperature

    • At what temperature does creep become significant for a material?

  • 0.4 Tm (correct)
  • 0.6 Tm
  • Tm
  • 0.8 Tm

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

  • Permanent dimensional change (correct)
  • Temporary dimensional change
  • Dimensional change only at higher temperatures
  • No dimensional change

    • What can result from sufficient strain or creep in a material?

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

    What is the creep mechanism that involves atomic diffusion and elongation of the grain in response to applied stress and temperature?

    <p>Diffusion-controlled process</p> Signup and view all the answers

    What happens to vacancies in the material’s microstructure during the creep mechanism involving atomic diffusion?

    <p>Migrate toward grain boundaries</p> Signup and view all the answers

    What is the main purpose of conducting a creep test?

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

    What is the significance of thermal activation of dislocations in the context of creep?

    <p>It allows dislocations to move under applied stress at elevated temperatures</p> Signup and view all the answers

    Why are turbine engine blades particularly susceptible to creep failure?

    <p>They experience sustained stress over time at high temperatures</p> Signup and view all the answers

    Which materials are susceptible to creep at relatively high temperatures according to the text?

    <p>Nickel-based superalloys</p> Signup and view all the answers

    Why is it important to ensure quality material fabrication and processing in order to reduce material defects and voids?

    <p>To reduce the susceptibility of the material to creep</p> Signup and view all the answers

    In which manner may creep failures appear according to the text?

    <p>Both ductile and brittle</p> Signup and view all the answers

    What do turbines, gas turbine engines, and ovens have in common according to the text?

    <p>They all undergo creep phenomenon</p> Signup and view all the answers

    What is the role of grain boundaries in accommodating applied stress in materials experiencing creep?

    <p>They allow dislocations to move along them</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 high temperatures</p> Signup and view all the answers

    What is the purpose of plotting data from a creep test as strain vs. time?

    <p>To visualize how strain changes over time under constant stress and temperature</p> Signup and view all the answers

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