32 Questions
What is creep in the context of material science?
Time-dependent deformation of a material under constant stress
When does creep become significant in a material?
When the temperature is greater than 0.4 Tm (melting temperature on an absolute scale)
Under what conditions does a material experience creep failure?
When the dimensional change renders the material useless in performing its intended function
What is the result of sufficient strain or creep in a material?
Fracture, known as stress rupture or creep fracture
Which process governs creep mechanisms?
Diffusion-controlled process
How do vacancies in a material's microstructure contribute to creep?
They migrate toward grain boundaries to fill the voids, resulting in elongation of the grain
What are the mechanisms of creep mentioned in the text?
Vacancies migrating along grain boundaries and dislocations moving to accommodate the applied stress
What can make materials susceptible to creep at different temperatures?
The quality of material fabrication and processing
What is a typical creep test measure?
Strain as a function of time at a constant stress and temperature
Which materials are mentioned as susceptible to creep at relatively high temperatures?
Nickel-based superalloys
Where do components that experience creep phenomenon exist?
Boilers, gas turbine engines, and ovens
What can cause creep failures to appear in a brittle manner?
High pressure steam lines
Why are materials with high melting temperatures often selected for turbine engine blades?
To withstand sustained stress over time at a relatively high temperature
What is the slope of the strain vs. time curve in a creep test?
The strain rate or creep rate of the material
What is an example application whereby components experience creep phenomenon?
Steam turbine blades
What can ceramics exhibit at extremely high temperatures?
A considerable amount of creep
Ceramics have a very low resistance to deformation by creep due to their characteristically low melting temperatures.
False
The rupture lifetime (tr) in a creep test is the time taken for the material to reach its maximum strain.
True
Thermal activation of dislocations refers to the reduction in energy required to move pinned dislocations at increasing temperatures.
False
Boilers, gas turbine engines, and ovens are examples of components that do not experience creep phenomenon.
False
Materials with high melting temperatures are often selected for turbine engine blades due to their resistance to creep at relatively high temperatures.
True
Creep failures always appear in a ductile manner.
False
In a creep test, strain is measured as a function of stress at a constant temperature.
False
Nickel-based superalloys are not susceptible to creep at relatively high temperatures.
False
Creep becomes significant in a material only at extremely high temperatures.
False
The slope of the strain vs. time curve in a creep test represents the strain rate of the material.
True
Creep is a time-independent deformation of a material subjected to a constant stress.
False
Creep is not influenced by temperature.
False
Creep failure occurs when the dimensional change of a material makes it unsuitable for its intended function.
True
Creep fracture is also known as elastic deformation.
False
Creep occurs when atoms move in response to the applied stress and temperature, filling the voids in the grains.
True
Materials with low melting temperatures are often selected for turbine engine blades.
False
Explore the concepts of creep failure, creep test, stress and temperature effects on creep behavior, and design against creep in mechanical engineering. This quiz covers Chapter 5 of the Fourth Year First Term curriculum, taught by Dr. Reham Reda Abbas.
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